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The amount of calcium released from the sarcoplasmic reticulum in skeletal muscle rapidly declines during repeated twitch contractions. In this study, we test the hypothesis that caffeine can mitigate these contraction-induced declines in calcium release. Lumbrical muscles were isolated from male C57BL/6 mice and loaded with the calcium-sensitive indicator, AM-furaptra. Muscles were then stimulated at 8 Hz for 2.0 s in the presence or absence of 0.5 mM caffeine, at either 30 [degrees]C or 37 [degrees]C. The amplitude and area of the furaptra-based intracellular calcium transients and force produced during twitch contractions were calculated. For each of these measures, the values for twitch 16 relative to twitch 1 were higher in the presence of caffeine than in the absence of caffeine at both temperatures. We conclude that caffeine can attenuate contraction-induced diminutions of calcium release during repeated twitch contractions, thereby contributing to the inotropic effects of caffeine. Key words: skeletal muscle, calcium-sensitive indicators, AM-furaptra, staircase, force potentiation, twitch. La quantite de calcium libere du reticulum sarcoplasmique du muscle squelettique diminue rapidement pendant des saccades de contractions repetees. Dans cette etude, nous tentons de verifier l'hypothese selon laquelle la cafeine peut attenuer ces diminutions de liberation de calcium engendrees par les contractions. Nous avons isole des muscles interosseux de souris C57BL/6 males et nous les avons charges d'AM-furaptra, un indicateur sensible au calcium. Nous avons ensuite stimule les muscles a 8 Hz pendant 2,0 s en presence ou en absence de cafeine a 0,5 mM, a 30 ou a 37 [degrees]C. Nous avons calcule la force developpee, ainsi que l'amplitude et la surface sous la courbe des courants intracellulaires de calcium transitoires obtenue a l'aide de furaptra pendant les saccades de contraction. Pour chacune de ces mesures, les valeurs etaient plus elevees pour la saccade 16 que pour la saccade 1 en presence de cafeine qu'en absence de cafeine, et ce, aux deux temperatures. Nous en arrivons a la conclusion que la cafeine peut entrainer une attenuation des diminutions de liberation de calcium engendrees par les contractions pendant des saccades de contraction repetees, ce qui contribuerait aux effets inotropes de la cafeine. [Traduit par la Redaction] Mots-cles: muscle squelettique, indicateurs sensibles au calcium, AM-furaptra, escalier, potentialisation de la force, saccade., Introduction The rise and fall of free myoplasmic [Ca.sup.2+] levels following a single depolarization is collectively termed the intracellular [Ca.sup.2+] transient (ICT) (Calderon et al. 2014). The amount of [Ca.sup.2+] [...]

The sarco(endo)plasmic reticulum calcium ATPase (SERCA) is responsible for transporting calcium ([Ca.sup.2+]) from the cytosol into the lumen of the sarcoplasmic reticulum (SR) following muscular contraction. The [Ca.sup.2+] sequestering activity of SERCA facilitates muscular relaxation in both cardiac and skeletal muscle. There are more than 10 distinct isoforms of SERCA expressed in different tissues. SERCA2a is the primary isoform expressed in cardiac tissue, whereas SERCA1a is the predominant isoform expressed in fast-twitch skeletal muscle. The [Ca.sup.2+] sequestering activity of SERCA is regulated at the level of protein content and is further modified by the endogenous proteins phospholamban (PLN) and sarcolipin (SLN). Additionally, several novel mechanisms, including post-translational modifications and microRNAs (miRNAs) are emerging as integral regulators of [Ca.sup.2+] transport activity. These regulatory mechanisms are clinically relevant, as dysregulated SERCA function has been implicated in the pathology of several disease states, including heart failure. Currently, several clinical trials are underway that utilize novel therapeutic approaches to restore SERCA2a activity in humans. The purpose of this review is to examine the regulatory mechanisms of the SERCA pump, with a particular emphasis on the influence of exercise in preventing the pathological conditions associated with impaired SERCA function. Key words: calcium ([Ca.sup.2+]), cardiac muscle, skeletal muscle, phospholamban (PLN), sarcolipin (SLN), exercise, post-translational modifications, heart failure. L'ATPase SERCA (<>) est responsable du transport du calcium ([Ca.sup.2+]) du cytosol a la lumiere du reticulum sarcoplasmique (RS) a la suite de la contraction musculaire. L'activite de sequestration de [Ca.sup.2+] de SERCA facilite la relaxation musculaire tant dans le muscle cardiaque que dans le muscle squelettique. Il existe plus de 10 formes distinctes de SERCA exprimees dans differents tissus. SERCA2a est la principale isoforme exprimee dans le tissu cardiaque alors que SERCAla est l'isoforme predominante du muscle squelettique a contraction rapide. L'activite de sequestration de [Ca.sup.2+] de SERCA est regulee au niveau du contenu en proteine, et elle est modifiee en plus par deux proteines endogenes, le phospholamban (PLN) et la sarcolipine (SLN). En outre, plusieurs mecanismes nouveaux, dont les modifications posttraductionnelles et les microARN (miARN) emergent maintenant en tant que regulateurs integraux de l'activite de transport du [Ca.sup.2+]. Ces mecanismes regulateurs sont pertinents sur le plan clinique, car la deregulation de la fonction de SERCA a ete impliquee dans plusieurs pathologies incluant l'insuffisance cardiaque. Actuellement, plusieurs essais cliniques en cours utilisent de nouvelles approches therapeutiques afin de retablir l'activite de SERCA2a chez l'humain. Le but de cet article de revue est d'examiner les mecanismes regulateurs de la pompe SERCA, en mettant l'emphase sur l'influence de l'exercice dans la prevention des conditions pathologiques associees a une deficience de la fonction de SERCA. [Traduit par la Redaction] Mots-cles: calcium ([Ca.sup.2+]), muscle cardiaque, muscle squelettique, phospholamban (PLN), sarcolipine (SLN), exercice, modifications post-traductionnelles, insuffisance cardiaque., Introduction The role of calcium in regulating muscular contraction Calcium ([Ca.sup.2+]) plays an integral role in regulating the process of excitation-contraction coupling (ECC) in both cardiac and skeletal muscle tissues. [...]

The intracellular scaffold protein IQGAP1 supports protein complexes in conjunction with numerous binding partners involved in multiple cellular processes. Here, we determined that IQGAP1 modulates airway smooth muscle contractility. Compared with WT controls, at baseline as well as after immune sensitization and challenge, [Iqgap.sup.1-/-] mice had higher airway responsiveness. Tracheal rings from [Iqgap1.sup.-/-] mice generated greater agonist-induced contractile force, even after removal of the epithelium. RhoA, a regulator of airway smooth muscle contractility, was activated in airway smooth muscle lysates from [Iqgap1.sup.-/-] mice. Likewise, knockdown of IQGAP1 in primary human airway smooth muscle cells increased RhoA activity. Immunoprecipitation studies indicated that IQGAP1 binds to both RhoA and p190A-RhoGAP, a GTPase-activating protein that normally inhibits RhoA activation. Proximity ligation assays in primary airway human smooth muscle cells and mouse tracheal sections revealed colocalization of p190A-RhoGAP and RhoA; however, these proteins did not colocalize in IQGAP1 knockdown cells or in [Iqgap1.sup.-/-] trachea. Compared with healthy controls, human subjects with asthma had decreased IQGAP1 expression in airway biopsies. Together, these data demonstrate that IQGAP1 acts as a scaffold that colocalizes p190A- RhoGAP and RhoA, inactivating RhoA and suppressing airway smooth muscle contraction. Furthermore, our results suggest that IQGAP1 has the potential to modulate airway contraction severity in acute asthma., Introduction In asthma, smooth muscle contraction leads to airway narrowing and resistance to airflow. Better understanding of the mechanisms that regulate airway smooth muscle contractility is important for the development [...]

Purpose: In this study, the authors compared indirect estimates of jaw-muscle tension in children with suspected muscle-tone abnormalities with age- and gender-matched controls. Method: Jaw movement and muscle activation were measured in children (ages 3 years, 11 months, to 10 years) with suspected muscle-tone abnormalities (Down syndrome or spastic cerebral palsy; n = 10) and controls (n = 11). Two measures were used to infer jaw tension: a kinematic index of mass-normalized stiffness and electromechanical delay (EMD). The kinematic index used video-based kinematics to obtain the slope of the peak velocity-displacement relationship. The EMD was derived from the interval between the onset of suprahyoid muscle activity and the onset of jaw depression. Results: Neither measure differentiated the groups. The kinematic index revealed differences between stressed and unstressed syllables in 3-syllable productions by the participants with cerebral palsy and controls, but not in 2-syllable productions by the participants with Down syndrome and controls. Conclusion: This preliminary investigation included the novel application of 2 measures to infer the jaw-muscle tension of children with suspected tone abnormalities. Although the results do not support the hypothesis that suspected muscle-tone abnormalities affect jaw movement sufficiently to influence speech production, considerations for interpreting the findings include methodological limitations and possible compensatory muscle coactivation. Key Words: cerebral palsy, Down syndrome, children, speech disorders, Low-level tonic agonist-antagonist muscle activity balanced against intrinsic muscle properties (e.g., elasticity) and joint properties is believed to maintain muscle length and tension in a state of movement readiness. Although [...]

ARTICLE INFO Keywords: Schisandra chinensis Lignans Smooth muscle relaxation Calcium channels ABSTRACT In this study, the herbal extracts of Schisandra chinensis were demonstrated to inhibit the contractions induced by acetylcholine [...]

There is evidence that nitric oxide (NO) is required for the normal increases in skeletal muscle glucose uptake during contraction, but the mechanisms involved have not been elucidated. We examined whether NO regulates glucose uptake during skeletal muscle contractions via cGMP-dependent or cGMP-independent pathways. Isolated extensor digitorum longus (EDL) muscles from mice were stimulated to contract ex vivo, and potential NO signaling pathways were blocked by the addition of inhibitors to the incubation medium. Contraction increased (P < 0.05) NO synthase (NOS) activity (40%) and dichlorofluorescein (DCF) fluorescence (a marker of oxidant levels; 95%), which was prevented with a NOS inhibitor [N.sup.G]-monomethyl-L-arginine (L-NMMA), and antioxidants [nonspecific antioxidant, N-acetylcysteine (NAC); thiol-reducing agent, DTT], respectively. L-NMMA and NAC both attenuated glucose uptake during contraction by 50% (P < 0.05), and their effects were not additive. Neither the guanylate cyclase inhibitor 1H-[1,2,4]oxadiazolo-[4,3-a]quinoxalin-l-one, which prevents the formation of cGMP, the cGMP-dependent protein (PKG) inhibitor Rp-8-bromo-[beta]-phenyl-l,N2ethenoguanosine 3',5'-cyclic monophosphorothioate sodium salt nor white light, which breaks S-nitrosylated bonds, affects glucose uptake during contraction; however, DTT attenuated (P < 0.05) contraction-stimulated glucose uptake (by 70%). NOS inhibition and antioxidant treatment reduced contraction-stimulated increases in protein S-glutathionylation and tyrosine nitration (P < 0.05), without affecting AMPK or p38 MAPK phosphorylation. In conclusion, we provide evidence to suggest that NOS-derived oxidants regulate skeletal muscle glucose uptake during ex vivo contractions via a cGMP/PKG-, AMPK-, and p38 MAPK-independent pathway. In addition, it appears that NO and ROS may regulate skeletal muscle glucose uptake during contraction through a similar pathway. reactive oxygen species; peroxynitrite; S-glutathionylation; AMP-activated protein kinase doi: 10.1152/ajpregu.00433.2010

Chronic heart failure (CHF) induces muscle fiber-type specific alterations in skeletal muscle [O.sub.2] delivery and utilization during metabolic transitions. As a result, the recovery of microvascular P[O.sub.2] ([MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII]) is prolonged in slow-twitch skeletal muscle but not fast-twitch skeletal muscle in rats with CHF. We tested the hypothesis that CHF slows [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] recovery in rat skeletal muscle of a mixed fiber-type analogous to human locomotory muscles and that the degree of slowing correlates with central indexes of heart failure. Healthy control [n = 6, left ventricular end-diastolic pressure (LVEDP): 10 [+ or -] 1 mmHg], moderate CHF (n = 6, LVEDP: 18 [+ or -] 2 mmHg), and severe CHF (n = 4, LVEDP: 34 [+ or -] 2 mmHg) female Sprague-Dawley rats had their fight spinotrapezius muscles (41% type I, 7% type IIa, and 52% type IIb and d/x) exposed, and [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] was measured via phosphorescence quenching during 180 s of recovery from 180 s of electrically induced twitch contractions (1 Hz, 4-6 V). CHF progressively slowed the mean response time (MRT; the time to reach 63% of the overall dynamic response) of [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] recovery ([MRT.sub.off]; control: 60.2 [+ or -] 6.9, moderate CHF: 72.8 [+ or -] 6.6, and severe CHF: 109.8 [+ or -] 6.6 s, P < 0.05 for all). [MRT.sub.off] correlated positively with central hemodynamic (LVEDP: r = 0.76, P < 0.01) and morphological (right ventricle-to-body weight ratio: r = 0.74, P < 0.01; and lung weight-to-body weight ratio: r = 0.79, P < 0.01) indexes of heart failure. The present investigation suggests that slowed [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] kinetics during recovery in CHF constitutes a mechanistic link between impaired circulatory and metabolic recovery after contractions in CHF. skeletal muscle; oxygen delivery; myocardial infarction; left ventricular end-diastolic pressure; phosphorescence quenching; partial pressure of oxygen doi: 10.1152/ajpheart.00590.2010.

Peak [Ca.sup.2+]-activated specific force (force/fiber cross-sectional area) of human chemically skinned vastus lateralis muscle fiber segments was determined before and after a fixed-end contraction or an eccentric contraction of standardized magnitude (+0.25 optimal fiber length) and velocity (0.50 unloaded shortening velocity). Fiber myosin heavy chain (MHC) isoform content was assayed by SDS-PAGE. Posteccentric force deficit, a marker of damage, was similar for type I and IIa fibers but threefold greater for type IIa/IIx hybrid fibers. A fixed-end contraction had no significant effect on force. Multiple linear regression revealed that posteccentric force was explained by a model consisting of a fiber type-independent and a fiber type-specific component ([r.sup.2] = 0.91). Preeccentric specific force was directly associated with a greater posteccentric force deficit. When preeccentric force was held constant, type I and IIa fibers showed identical susceptibility to damage, while type IIa/IIx fibers showed a significantly greater force loss. This heightened sensitivity to damage was directly related to the amount of type IIx MHC in the hybrid fiber. Our model reveals a fiber-type sensitivity of the myofilament lattice or cytoskeleton to mechanical strain that can be described as follows: type IIa/IIx > type IIa = type I. If these properties extend to fibers in vivo, then alterations in the number of type IIa/IIx fibers may modify a muscle's susceptibility to eccentric damage. lengthening contraction; pliometric contraction; muscle damage; myosin heavy chain doi: 10.1152/ajpcell.00226.2010.

It has been accepted for half a century that, for a given level of activation, the steady-state isometric force of a muscle sarcomere depends exclusively on the amount of overlap between the contractile filaments actin and myosin, or equivalently sarcomere length (Gordon AM et al., J Physiol 184: 170-192, 1966). Moreover, according to the generally accepted paradigm of muscle contraction, the cross-bridge theory (Huxley AF, Prog Biophys Biophys Chem 7: 255-318, 1957), this steady-state isometric sarcomere force is independent of the muscle's contractile history (Huxley AF, Prog Biophys Biophys Chem 7: 255-318, 1957; Walcott S and Herzog W, Math Biosci 216: 172-186, 2008); i.e., it is independent of whether a muscle is held at a constant length before and during the contraction or whether the muscle is shortened or lengthened to the same constant length. This, however, is not the case, as muscles and single fibers that are stretched show greatly increased steady-state isometric forces compared with preparations that are held at a constant length (Abbott BC and Aubert XM, J Physiol 117: 77-86, 1952; De Ruiter CJ et al., J Physiol 526.3: 671-681, 2000; Edman KAP et al., J Physiol 281: 139-155, 1978; Edman KAP et al., J Gen Physiol 80: 769-784, 1982; Edman KAP and Tsuchiya T, J Physiol 490.1: 191-205, 1996). This so-called 'residual force enhancement' (Edman KAP et al., J Gen Physiol 80: 769-784, 1982) offers a perplexing puzzle for muscle physiologists. Many theories have been advanced to address the discrepancy between prediction and observation with the most popular and accepted being the sarcomere length nonuniformity theory (Morgan DL, Biophys J 57: 209221, 1990), which explains the residual force enhancement with the development of large nonuniformities in sarcomere lengths during muscle stretching. Here, we performed experiments in mechanically isolated sarcomeres and observed that the residual force enhancement following active stretching is preserved. Since our preparation utilizes a single sarcomere, a redistribution of the length of neighboring sarcomeres to produce the higher force following stretch is, by design, precluded. Furthermore, the enhanced forces in the single sarcomeres always exceed the isometric forces on the plateau of the force-length relationship, thereby eliminating the possibility that our result might have been obtained because of a redistribution of half-sarcomere lengths. Since force enhancement in single myofibrils has been associated with actin-titin interactions (Kulke Met al., Circ Res 89: 874-881, 2001; Li Q et al., Biophys J 69: 1508-1518, 1995) and calcium binding to titin (Joumaa Vet al., Am J Physiol Cell Physiol 294: C74-C78, 2008; Labeit D et al., Proc Natl Acad Sci USA 100: 13716-13721, 2003), titin may regulate the sarcomeric force enhancement observed here. doi: 10.1152/ajpcell.00222.2010.

The heat liberated upon stress production in isolated cardiac muscle provides insights into the complex thermodynamic processes underlying mechanical contraction. To that end, we simultaneously measured the heat and stress (force per cross-sectional area) production of cardiac trabeculae from rats using a flow-through micromechanocalorimeter. In a flowing stream of [O.sub.2]-equilibrated Tyrode solution (~22[degrees]C), the stress and heat production of actively contracting trabeculae were varied by 1) altering stimulus frequency (0.2-4 Hz) at optimal muscle length ([L.sub.o]), 2) reducing muscle length below [L.sub.o] at 0.2 and 2 Hz, and 3) changing extracellular [Ca.sup.2+] concentrations ([[[Ca.sup.2+]].sub.o]; 1 and 2 mM). Linear regression lines were adequate to fit the active heat-stress data. The active heat-stress relationships were independent of stimulus frequency and muscle length but were dependent on [[[Ca.sup.2+]].sub.o], having greater intercepts at 2 mM [[[Ca.sup.2+]].sub.o] than at 1 mM [[[Ca.sup.2+]].sub.o] (3.5 and 2.0 kJ x [m.sup.-3] x [twitch.sup.-1], respectively). The slopes among the heat-stress relationships did not differ. At the highest experimental stimulus frequency, pronounced elevation of diastolic [Ca.sup.2+] resulted in incomplete twitch relaxation. The resulting increase of diastolic stress, which occurred with negligible metabolic energy expenditure, subsequently diminished due to the time-dependent loss of myofilament [Ca.sup.2+]-sensitivity. cardiac thermodynamics; heat-stress relationships; dynamic stiffness; diastolic calcium, myofilament calcium sensitivity doi: 10.1152/ajpheart.00454.2010.

Microfibrils are macromolecular complexes associated with elastin to form elastic fibers that endow extensible tissues, such as arteries, lungs, and skin, with elasticity property. Fibrillin-1, the main component of microfibrils, is a 350-kDa glycoprotein for which genetic haploin-sufficiency in humans can lead to Marfan syndrome, a severe poly-featured pathology including aortic aneurysms and dissections. Microfibrils and fibrillin-1 fragments mediate adhesion of several cell types, including endothelial ceils, while fibrillin-1 additionally triggers lung and mesangial cell migration. However, fibrillin-l-induced intracellular signaling is unknown. We have studied the signaling events induced in human umbilical venous endothelial cells (HUVECs) by aortic microfibrils as well as recombinant fibrillin-1 Arg-Gly-Asp (RGD)-containing fragments PF9 and PF14. Aortic microfibrils and PF14, not PF9, substantially and dose dependently increased HUVEC cytoplasmic and nuclear calcium levels measured using the fluorescent dye Fluo-3. This effect of PF14 was confirmed in bovine aortic endothelial cells. PF14 action in HUVECs was mediated by [alpha]v[beta]3 and [alpha]5[beta]1 integrins, phospholipase-C, inosital 1,4,5-trisphosphate, and mobilization of intracellular calcium stores, whereas membrane calcium channels were not or only slightly implicated, as shown in patch-clamp experiments. Finally, PF14 enhanced endothelial cell proliferation and migration. Hence, fibrillin-1 sequences may physiologically activate endothelial cells. Genetic fibrillin-1 deficiency could alter normal endothelial signaling and, since endothelium dysfunction is an important contributor to Marfan syndrome, participate in the arterial anomalies associated with this developmental disease. adhesion; calcium signaling; Marfan syndrome doi: 10.1152/ajpcell.00377.2009.

Nerve-released ACh is the main stimulus for contraction of urinary bladder smooth muscle (UBSM). Here, the mechanisms by which ACh contracts UBSM are explored by determining [Ca.sup.2+] and electrical signals induced by nerve-released ACh. Photolysis of caged inositol 1,4,5-trisphosphate ([IP.sub.3]) evoked [Ca.sup.2+] release from the sarcoplasmic reticulum. Electrical field stimulation (20 Hz) induced [Ca.sup.2+] waves within the smooth muscle that were present only during stimulus application. [Ca.sup.2+] waves were blocked by inhibition of muscarinic ACh receptors (mAChRs) with atropine and depletion of sarcoplasmic reticulum [Ca.sup.2+] stores with cyclopiazonic acid (CPA), and therefore likely reflect activation of [IP.sub.3] receptors ([IP.sub.3]Rs). Electrical field stimulation also increased excitability to induce action potentials (APs) that were accompanied by [Ca.sup.2+] flashes, reflecting [Ca.sup.2+] entry through voltage-dependent [Ca.sup.2+] channels (VDCCs) during the action potential. The evoked [Ca.sup.2+] flashes and APs occurred as a burst with a lag time of ~1.5 s after onset of stimulation. They were not inhibited by blocking [IP.sub.3]-mediated [Ca.sup.2+] waves, but by blockers of mAChRs (atropine) and VDCCs (diltiazem). Nerve-evoked contractions of UBSM strips were greatly reduced by blocking VDCCs, but not by preventing [IP.sub.3]-mediated [Ca.sup.2+] signaling with cyclopiazonic acid or inhibition of PLC with U73122. These results indicate that ACh released from nerve varicosities induces [IP.sub.3]-mediated [Ca.sup.2+] waves during stimulation; but contrary to expectations, these signals do not appear to participate in contraction. In addition, our data provide compelling evidence that UBSM contractions evoked by nerve-released ACh depend on increased excitability and the resultant [Ca.sup.2+] entry through VDCCs during APs. muscarinic receptor; sarcoplasmic reticulum; [IP.sub.3] receptor; voltage- dependent calcium channel doi: 10.1152/ajpregu.00180.2010.

The role of adenosine and contraction for secretion of vascular endothelial growth factor (VEGF) in skeletal muscle was investigated in human subjects and rat primary skeletal muscle cells. Microdialysis probes were inserted in the thigh muscle of seven male subjects, and dialysate was collected at rest, during infusion of adenosine, and during knee extensor exercise. The dialysate was analyzed for content of VEGF protein and adenosine. The mechanism of VEGF secretion from muscle cells in culture was examined in resting and electrostimulated cells and in response to the adenosine analog NECA and the adenosine [A.sub.2A] receptor specific analog CGS-21680. Adenosine receptors [A.sub.1], [A.sub.2A], and [A.sub.2B] were blocked with DPCPX, ZM-241385, and enprofylline, respectively, cAMP-dependent protein kinase A (PKA) and mitogen-activated protein kinase (MAPK) were inhibited by H-89 and PD-98509, respectively. The human experiment showed that adenosine infusion enhanced (P < 0.05) the interstitial concentration of VEGF protein approximately fourfold above baseline. Exercise increased (P < 0.05) the interstitial VEGF concentration approximately sixfold above rest in parallel with an approximately threefold increase in adenosine concentration. In accordance, in cultured muscle cells, NECA and contraction caused secretion of VEGF (P < 0.05). The contraction-induced secretion of VEGF was abolished by the [A.sub.2B] antagonist enprofylline and by inhibition of PKA or MAPK. The results demonstrate that adenosine causes secretion of VEGF from human skeletal muscle cells and that the contraction-induced secretion of VEGF protein is partially mediated via adenosine acting on [A.sub.2B] adenosine receptors. Moreover, the contraction-induced secretion of VEGF protein from muscle is dependent on both PKA and MAPK activation, but only the MAPK pathway appears to be adenosine dependent, revealing involvement of additional pathways in VEGF secretion. vascular endothelial growth factor doi: 10.1152/ajpheart.00082.2010.

Garcia-Lopez, D, Herrero, AJ, Gonzalez-Calvo, G, Rhea, MR, and Marin, PJ. Influence of 'in series' elastic resistance on muscular performance during a biceps-curl set on the cable machine. J Strength Cond Res 24(9): 2449-2455, 2010--This study aimed to investigate the role of elastic resistance (ER) applied 'in series' to a pulley-cable (PC) machine on the number of repetitions performed, kinematics parameters, and perceived exertion during a biceps-curl set to failure with a submaximal load (70% of the 1 repetition maximum). Twenty-one undergraduate students (17 men and 4 women) performed, on 2 different days, 1 biceps-curl set on the PC machine. Subjects were randomly assigned to complete 2 experimental conditions in a cross-over fashion: conventional PC mode or ER + PC mode. Results indicate ER applied 'in series' to a PC machine significantly reduces (p < 0.05) the maximal number of repetitions and results in a smooth and consistent decline in mean acceleration throughout the set, in comparison to the conventional PC mode. Although no significant differences were found concerning intrarepetition kinematics, the ER trended to reduce (18.6%) the peak acceleration of the load. With a more uniformly distributed external resistance, a greater average muscle tension could have been achieved throughout the range of movement, leading to greater fatigue that could explain the lower number of maximal repetitions achieved. The application of force in a smooth, consistent fashion during each repetition of an exercise, while avoiding active deceleration, is expected to enhance the benefits of the resistance exercise, especially for those seeking greater increases in muscular hypertrophy. KEY WORDS elastic tension, accommodate resistance, weight training, kinematics, muscle tension

The purpose of this study was to examine (a) the mechanical power and the electromyographic (EMG) activity during a moderate load muscular endurance session and (b) the maximal mechanical power output and EMG activity using a light load and a heavy load afterward. Sixteen men (age: 20.7 [+ or -] 1.1 years) performed 4 sets of 20 repetitions with an initial load of 50% of 1 repetition maximum (1RM), and 2 minutes of rest, in the squat exercise. Furthermore, the subjects performed 4 repetitions with loads of 40 and 80% of 1RM before, immediately after, and 30 minutes after the end of the session. Average power and EMG activity from vastus medialis (VM), vastus lateralis (VL), and rectus femoris (RF) were recorded during the concentric phase of the lift. Average power did not change during the first 2 sets, while it decreased (p < 0.05) during the third and the fourth set. Average quadriceps (AQ), VM, VL, and RF activity increased (p < 0.05) until the 11th repetition, approximately, during each set while it increased gradually from set to set. Maximal power and AQ, VM, and VL activity with the loads of 40 and 80% of 1RM were decreased (p < 0.05) after the session. Blood lactate reached 10.2 [+ or -] 2.5 and 13.1 [+ or -] 4.1 mmol x [L.sup.-1] after the second and the fourth set, respectively. It appears that during a muscular endurance session with submaximal power output, mechanical performance may gradually decrease, probably due to metabolic fatigue, while muscle electrical activity may increase. Following this type of a session, maximal power output and muscle activation with a light and especially with a heavy load are reduced. KEY WORDS weight training, fatigue, lactate, muscle activity, performance

This study examined the force/velocity (F/V) curve morphology among the entire concentric phase of the countermovement squat (CMS). The hypothesis is that F/V curve shape of the lower limb muscles complex is different from F/V isolated muscle curve and that these analyses could be useful in characterizing athletes' muscular capacity and training programs. Squat exercise was performed by 29 subjects (15 men and 14 women, divided into resistance and endurance athletes). The protocol was 6 x 1 CMS at maximal speed with increasing loads: 20, 35, 50, 65, 80, 90% of 1 repetition maximum (1RM). Displacement, speed, and acceleration of the weight bar, joint knee angles, knee angular speed, and total and normalized forces were collected. F/V relation was obtained by force and velocity values of each 10[degrees] angular interval of the concentric phase for any load. Results show that the F/V relationship does not follow a linear shape and an equivalent criterion for all loads. We observed a 'second peak force' statistically higher (p < 0.05) than the inversion peak at 80 and 90% 1RM. Resistance trained men showed a 'second peak' higher and larger than that shown by endurance trained men. This indicated a higher ability to produce and maintain greater force at higher relative speed. These results may be helpful to identify the muscle characteristics of the athletes at various speeds and joint positions. With a phase division of the specific move, it will be possible to determine an individualized program to monitor the specific phases of technical moves and to evaluate the training effect in long run. KEY WORDS squat, encoder, lower limbs

This study aimed to determine whether high-intensity dumbbell exercise involving both concentric and eccentric contractions would provide a temporary alleviation of delayed-onset muscle soreness (DOMS). It also examined the effect of alleviated muscle soreness on dynamic muscle performance using a stretch-shortening cycle (SSC; peak angular acceleration and velocity of the elbow during both lowering and concentric phases) to provide indirect evidence that DOMS contributes to the dynamic performance decrement after eccentric injury. Thirteen untrained adults performed 30 maximal isokinetic eccentric contractions of the elbow flexors to induce eccentric damage. Five sets of arm curls using a dumbbell (equivalent to 70% of isometric maximal voluntary contraction) were then performed until failure on days 1, 2, 3, and 5 of recovery. Muscle soreness significantly decreased after each session of dumbbell exercise (p = 0.001). Isometric strength further decreased immediately after dumbbell exercise, indicating muscle fatigue (p < 0.001). Dynamic performance variables were less affected by fatigue, however, with performance being reduced only for peak lowering velocity (p < 0.001). Other measures of dynamic performance were relatively constant after dumbbell exercise, particularly on days 2 and 3 when soreness was greatest. It was concluded that high-intensity concentric/eccentric dumbbell exercise was able to temporarily alleviate DOMS and that this reduction in soreness served to counter the effect of peripheral muscle fatigue during dynamic activities. Practical applications of this study are that after eccentric damage, alleviation of muscle soreness through an optimal warm-up may be helpful to temporarily recover dynamic muscle performance. Free-weight loading is one suggested technique to temporarily manage DOMS. KEY WORDS exercise-induced analgesia, DOMS, isometric strength, stretch-shortening cycle

The objective of the present study was to investigate the effects of static and dynamic stretching alone and in combination on subsequent agility, sprinting, and jump performance. Eight different stretching protocols: (a) static stretch (SS) to point of discomfort (POD); (b) SS less than POD (SS KEY WORDS flexibility, stretch sequence, stretch intensity

Catenin is an 88-kDa member of the armadillo family of proteins that is associated with the cadherin-catenin complex in the plasma membrane. This complex interacts dynamically with the actin cytoskeleton to stabilize adherens junctions, which play a central role in force transmission by smooth muscle cells. Therefore, in the present study, we hypothesized a role for [beta]-catenin in the regulation of smooth muscle force production. [beta]-Catenin colocalized with smooth muscle [alpha]-actin (sm-[alpha]-actin) and N-cadherin in plasma membrane fractions and coimmunoprecipitated with sm-[alpha]-actin and N-cadherin in lysates of bovine tracheal smooth muscle (BTSM) strips. Moreover, immunocytochemistry of cultured BTSM cells revealed clear and specific colocalization of sm-[alpha]-actin and [beta]-catenin at the sites of cell-cell contact. Treatment of BTSM strips with the pharmacological [beta]-catenin/T cell factor-4 (TCF4) inhibitor PKFl15-584 (100 nM) reduced [beta]-catenin expression in BTSM whole tissue lysates and in plasma membrane fractions and reduced maximal KC1- and methacholine-induced force production. These changes in force production were not accompanied by changes in the expression of sm-[alpha]-actin or sin-myosin heavy chain (MHC). Likewise, small interfering RNA (siRNA) knockdown of [beta]-catenin in BTSM strips reduced [beta]-catenin expression and attenuated maximal KCl- and methacholine-induced contractions without affecting sm-[alpha]actin or sm-MHC expression. Conversely, pharmacological (SB216763, LiC1) or insulin-induced inhibition of glycogen synthase kinase-3 (GSK-3) enhanced the expression of [beta]-catenin and augmented maximal KC1- and methacholine-induced contractions. We conclude that [beta]-catenin is a plasma membrane-associated protein in airway smooth muscle that regulates active tension development, presumably by stabilizing cell-cell contacts and thereby supporting force transmission between neighboring cells. asthma; cadherin; GSK-3 doi: 10.1152/ajplung.00020.2010.

In decerebrated rats, we determined the pressor and cardioaccelerator reflex responses to static contraction of hindlimb muscles whose femoral arteries were either occluded 72 h before contraction, occluded 3 min before contraction, or freely perfused. We found that the pressor reflex arising from the limb whose femoral artery was occluded for 72 h before contraction (32 [+ or -] 5 mmHg, n = 16) was significantly higher than the pressor reflex arising from the contralateral freely perfused limb (15 [+ or -] 3 mmHg, n = 16, P < 0.001) or than that arising from the contralateral limb whose femoral artery was occluded for only 3 min (17 [+ or -] 4 mmHg, n = 16, P < 0.001). Moreover, the pressor reflex arising from the limb whose femoral artery was occluded for 3 rain before the start of contraction was not significantly different than that arising from the contralateral freely perfused limb (n = 16, P = 0.819). The pressor component of the reflex arising from the limb whose femoral artery was occluded for 72 h was not changed by transient receptor potential vanilloid (TRPV) 1 receptor blockade with iodo-resiniferatoxin (n = 15, P = 0.272), although the cardio-accelerator component was significantly reduced (P = 0.005). In addition, the pressor response evoked by capsaicin injection in the femoral artery of the 72-h occluded limb was more than double that evoked from the freely perfused limb (P = 0.026). We conclude that chronic (i.e., 72 h) but not acute (3 min), femoral arterial occlusion augments pressor reflex arising from contraction of hindlimb muscles and that TRPV1 receptors play little role in this augmentation. static contraction; thin fiber muscle afferents; ischemia; neural control of circulation doi: 10.1152/ajpheart.00141.2010.

Mucus secretion from individual tracheal glands in adult ferrets was studied with time-lapse optical imaging of mucus droplets under an oil layer. Density of functional glands (determined by responses to 1 [micro]M carbachol) was 1.5 [+ or -] 0.3 per [mm.sup.2] (n = 6). Secretion rates (in pl x [min.sup.-1] x [gland.sup.-l]) were as follows: 4.1 [+ or -] 0.7 basal (unstimulated; n = 27, 669 glands), 338 [+ or -] 70 to 10 [micro]M forskolin (n = 8, 90 glands), 234 [+ or -] 13 to 1 [micro]M VIP (n = 6, 57 glands), 183 [+ or -] 92 to 10 [micro]M isoproterenol (n = 3, 33 glands), 978 [+ or -] 145 to 1 [micro]M carbachol (n = 11, 131 glands), and 1,348 [+ or -] 325 to 10 [micro]M phenylephrine (n = 7, 74 glands). The potency ([EC.sub.50], in [micro]M) and efficacy ([V.sub.max], in pl x [min.sup.-1] x [gland.sup.-1]) were 7.6 ([EC.sub.50]) and 338 [+ or -] 16 ([V.sub.max]) to forskolin, 1.0 ([EC.sub.50]) and 479 [+ or -] 19 ([V.sub.max]) to VIP, 0.6 ([EC.sub.50]) and 1,817 [+ or -] 268 ([V.sub.max]) to carbachol, and 3.7 ([EC.sub.50]) and 1,801 [+ or -] 95 ([V.sub.max]) to phenylephrine. Although carbachol and phenylephrine were equally effective secretagogues, only carbachol caused contractions of the trachealis muscle. Synergy was demonstrated between 300 nM isoproterenol and 100 nM carbachol, which, when combined, produced a secretion rate almost fourfold greater than predicted from their additive effect. The dependence of fluid secretion on [Cl.sup.-] and HC[O.sup.-.sub.3] varied depending on the mode of stimulation. Secretion stimulated by VIP or forskolin was reduced by ~60% by blocking either anion, while carbachol-stimulated secretion was blocked 68% by bumetanide and only 32% by HEPES replacement of HC[O.sup.-.sub.3]. These results provide parametric data for comparison with fluid secretion from glands in ferrets lacking CFFR. cystic fibrosis transmembrane conductance regulator; airway; adrenergic; cholinergic; muscle contraction doi: 10.1152/ajplung.00049.2010.

Contraction of detrusor smooth muscle (DSM) at short muscle lengths generates a stiffness component we termed adjustable passive stiffness (APS) that is retained in tissues incubated in a [Ca.sup.2+]-free solution, shifts the DSM length-passive tension curve up and to the left, and is softened by muscle strain and release (strain softened). In the present study, we tested the hypothesis that APS is due to slowly cycling actomyosin cross bridges. APS and active tension produced by the stimulus, KCl, displayed similar length dependencies with identical optimum length values. The myosin II inhibitor blebbistatin relaxed active tension maintained during a KCl-induced contraction and the passive tension maintained during stress-relaxation induced by muscle stretch in a [Ca.sup.2+]-free solution. Passive tension was attributed to tension maintaining rather than tension developing cross bridges because tension did not recover after a rapid 10% stretch and release as it did during a KCl-induced contraction. APS generated by a KCl-induced contraction in intact tissues was preserved in tissues permeabilized with Triton X-100. Blebbistatin and the actin polymerization inhibitor latrunculin-B reduced the degree of APS generated by a KCl-induced contraction. The degree of APS generated by KC1 was inhibited to a greater degree than was the peak KCl-induced tension by rhoA kinase and cyclooxygenase inhibitors. These data support the hypothesis that APS is due to slowly cycling actomyosin cross bridges and suggest that cross bridges may play a novel role in DSM that uniquely serves to ensure proper contractile function over an extreme working length range. urinary bladder; muscle mechanics; Triton X-100 permeabilization; Rho-kinase doi: 10.1152/ajprenal.00635.2009.

The world' s elderly population is expanding rapidly, and we are now faced with the significant challenge of maintaining or improving physical activity, independence, and quality of life in the elderly. Counteracting the progressive loss of muscle mass that occurs in the elderly, known as sarcopenia, represents a major hurdle in achieving these goals. Indirect evidence for a role of inflammation in sarcopenia is that markers of systemic inflammation correlate with the loss of muscle mass and strength in the elderly. More direct evidence is that compared with skeletal muscle of young people, the number of macrophages is lower, the gene expression of several cytokines is higher, and stress signaling proteins are activated in skeletal muscle of elderly people at rest. Sarcopenia may also result from inadequate repair and chronic maladaptation following muscle injury in the elderly. Macrophage infiltration and the gene expression of certain cytokines are reduced in skeletal muscle of elderly people compared with young people following exercise-induced muscle injury. Further research is required to identify the cause(s) of inflammation in skeletal muscle of elderly people. Additional work is also needed to expand our understanding of the cells, proteins, and transcription factors that regulate inflammation in the skeletal muscle of elderly people at rest and after exercise. This knowledge is critical for devising strategies to restrict sarcopenia, and improve the health of today's elderly population. sarcopenia; cytokines; macrophages; exercise doi: 10.1152/ajpregu.00467.2009.

Activity-induced elevation of extracellular purines and pyrimidines has been associated with autocrine and paracrine signaling in many tissues. Here we investigate the effect of purinergic signaling for the excitability and contractility of depolarized skeletal muscle. Muscle excitability was experimentally depressed by elevating the extracellular [K.sup.+] from 4 to 10 mM, which reduced the tetanic force to 24 [+ or -] 2% of the force at 4 mM [K.sup.+]. Upon addition of 1 mM ATP, however, the force recovered to 65 [+ or -] 8% of the control force (P < 0.001, n = 5). A similar recovery was seen with ADP, but not with UTP or adenosine. The ATP-induced force recovery could be inhibited by [P2Y.sub.1] receptor antagonists (3 [micro]M SCH-202676 or 1 [micro]M MRS-2500). A fourfold increase in M-wave area demonstrated that the ATP-induced force recovery was associated with restoration of muscle excitability (P < 0.05, n = 4). Experiments using [sup.86][Rb.sup.+] as a tracer for [K.sup.+] showed that ATP also induced a twofold increase in the activity of muscle [Na.sup.+]-[K.sup.+] pumps. The force recovery and the stimulation of the [Na.sup.+]-[K.sup.+] pump activity by ATP were inhibited by 50 [micro]M of the phospholipase C inhibitor U-73122. It is concluded that purinergic signaling can increase the [Na.sup.+]-[K.sup.+] pump activity and improve force and excitability of depolarized skeletal muscles. This novel purinergic regulation may be important for the maintenance of muscle excitability during intense exercise, where the extracellular [K.sup.+] can increase substantially. adenosine 5'-triphosphate disodium salt; adenosine 5'-diphosphate sodium salt; purinoceptors; M-wave; muscle contraction; phospholipase C doi: 10.1152/ajpcell.00361.2009.

Antispasmodics are used clinically to treat a variety of gastrointestinal disorders by inhibition of smooth muscle contraction. The main pathway for smooth muscle [Ca.sup.2+] entry is through L-type channels; however, there is increasing evidence that T-type [Ca.sup.2+] channels also play a role in regulating contractility. Otilonium bromide, an antispasmodic, has previously been shown to inhibit L-type [Ca.sup.2+] channels and colonic contractile activity. The objective of this study was to determine whether otilonium bromide also inhibits T-type [Ca.sup.2+] channels. Whole cell currents were recorded by patch-clamp technique from HEK293 cells transfected with cDNAs encoding the T-type [Ca.sup.2+] channels, Cav3.1 ([alpha]1G), Cav3.2 [alpha]1H), or Cav3.3 ([alpha]ll) alpha subunits. Extracellular solution was exchanged with otilonium bromide (10-8 to 10-5 M). Otilonium bromide reversibly blocked all T-type [Ca.sup.2+] channels with a significantly greater affinity for Cav3.3 than Cav3.1 or Cav3.2. Additionally, the drug slowed inactivation in Cav3.1 and Cav3.3. Inhibition of T-type [Ca.sup.2+] channels may contribute to inhibition of contractility by otilonium bromide. This may represent a new mechanism of action for antispasmodics and may contribute to the observed increased clinical effectiveness of antispasmodics compared with selective L-type [Ca.sup.2+] channel blockers. ammonium; antispasmodic; voltage dependence; intestine; smooth muscle doi: 10.1152/ajpgi.00437.2009.

Muscle contraction stimulates glucose uptake acutely to increase energy supply, but suitable cellular models that faithfully reproduce this complex phenomenon are lacking. To this end, we have developed a cellular model of contracting [C.sub.2][C.sub.12] myotubes overexpressing GLUT4 with an exofacial mycepitope tag (GLUT4myc) and explored stimulation of GLUT4 traffic by physiologically relevant agents. Carbachol (an acetylcholine receptor agonist) induced a gain in cell surface GLUT4myc that was mediated by nicotinic acetylcholine receptors. Carbachol also activated AMPK, and this response was sensitive to the contractile myosin ATPase inhibitor N-benzyl-p-toluenesulfonamide. The gain in surface GLUT4myc elicited by carbachol or by the AMPK activator 5-amino-4-carboxamide-1 [beta]-ribose was sensitive to chemical inhibition of AMPK activity by compound C and partially reduced by siRNA-mediated knockdown of AMPK catalytic subunits or LKB1. In addition, the carbachol-induced gain in cell surface GLUT4myc was partially sensitive to chelation of intracellular calcium with BAPTA-AM. However, the carbachol-induced gain in cell surface GLUT4myc was not sensitive to the CaMKK inhibitor STO-609 despite expression of both isoforms of this enzyme and a rise in cytosolic calcium by carbachol. Therefore, separate AMPK- and calcium-dependent signals contribute to mobilizing GLUT4 in response to carbachol, providing an in vitro cell model that recapitulates the two major signals whereby acute contraction regulates glucose uptake in skeletal muscle. This system will be ideal to further analyze the underlying molecular events of contraction-regulated GLUT4 traffic. carbachol; glucose transporter 4; adenosine 5'-monophosphate-activated protein kinase; acetylcholine doi:10.1152/ajpendo.00773.2009.

The cellular mechanisms whereby prior exercise enhances insulin-stimulated glucose transport (GT) are not well understood. Previous studies suggested that a prolonged increase in phosphorylation of Akt substrate of 160 kDa (AS160) may be important for the postexercise increase in insulin sensitivity. In the current study, the effects of in vivo exercise and in vitro contraction on subsequent insulin-stimulated GT were studied separately and together. Consistent with results from previous studies, prior exercise resulted in an increase in AS 160 [sup.642]Thr phosphorylation immediately after exercise in rat epitrochlearis muscles, and this increase remained 3 h postexercise concomitant with enhanced insulin-stimulated GT. For experiments with in vitro contraction, isolated rat epitrochlearis muscles were electrically stimulated to contract in the presence or absence of rat serum. As expected, insulin-stimulated GT measured 3 h after electrical stimulation in serum, but not after electrical stimulation without serum, exceeded resting controls. Immediately after electrical stimulation with or without serum, phosphorylation of both AS160 (detected by phospho-Akt substrate, PAS, antibody, or phospho-[sup.642]Thr antibody) and its paralog TBC1D1 (detected by phospho-[sup.237]Ser antibody) was increased. However, both AS 160 and TBC1D1 phosphorylation had reversed to resting values at 3 h poststimulation with or without serum. Increasing the amount of exercise (from 1 to 2 h) or electrical stimulation (from 5 to 10 tetani) did not further elevate insulin-stimulated GT. In contrast, the combination of prior exercise and electrical stimulation had an additive effect on the subsequent increase in insulin-stimulated GT, suggesting that these exercise and electrical stimulation protocols may amplify insulin-stimulated GT through distinct mechanisms, with a persistent increase in AS 160 phosphorylation potentially important for increased insulin sensitivity after exercise, but not after in vitro contraction. insulin sensitivity; Akt substrate of 160 kDa; TBC1D1; TBC1D4; glucose transporter 4 doi: 10.1152/ajpendo.00758.2009.

Skeletal muscle, during periods of exertion, experiences several different fatigue-based changes in contractility, including reductions in force, velocity, power output, and energy usage. The fatigue-induced changes in contractility stem from many different factors, including alterations in the levels of metabolites, oxidative damage, and phosphorylation of the myosin regulatory light chain (RLC). Here, we measured the direct molecular effects of fatigue-like conditions on actomyosin's unloaded sliding velocity using the in vitro motility assay. We examined how changes in ATP, ADP, [P.sub.i], and pH affect the ability of the myosin to translocate actin and whether the effects of each individual molecular species are additive. We found that the primary causes of the reduction in unloaded sliding velocity are increased [ADP] and lowered pH and that the combined effects of the molecular species are nonadditive. Furthermore, since an increase in RLC phosphorylation is often associated with fatigue, we examined the differential effects of myosin RLC phosphorylation and fatigue on actin filament velocity. We found that phosphorylation of the RLC causes a 22% depression in sliding velocity. On the other hand, RLC phosphorylation ameliorates the slowing of velocity under fatigue-like conditions. We also found that phosphorylation of the myosin RLC increases actomyosin affinity for ADP, suggesting a kinetic role for RLC phosphorylation. Furthermore, we showed that ADP binding to skeletal muscle is load dependent, consistent with the existence of a load-dependent isomerization of the ADP bound state. motility assay; RLC; load-dependent kinetics; skeletal muscle doi: 10.1152/ajpregu.00566.2009.

During skeletal muscle excitation-contraction (EC) coupling, membrane depolarizations activate the sarcolemmal voltage-gated L-type [Ca.sup.2+] channel ([Ca.sub.v]1.1). [Ca.sub.v]1.1 in turn triggers opening of the sarcoplasmic [Ca.sup.2+] release channel (RyR1) via interchannel protein--protein interaction to release [Ca.sup.2+] for myofibril contraction. Simultaneously to this EC coupling process, a small and slowly activating [Ca.sup.2+] inward current through [Ca.sub.v]1.1 is found in mammalian skeletal myotubes. The role of this [Ca.sup.2+] influx, which is not immediately required for EC coupling, is still enigmatic. Interestingly, whole-cell patch clamp experiments on freshly dissociated skeletal muscle myotubes from zebrafish larvae revealed the lack of such [Ca.sup.2+] currents. We identified two distinct isoforms of the pore-forming [Ca.sub.v]1.1[[alpha].sub.1S] subunit in zebrafish that are differentially expressed in superficial slow and deep fast musculature. Both do not conduct [Ca.sup.2+] but merely act as voltage sensors to trigger opening of two likewise tissue-specific isoforms of RyR1. We further show that non-[Ca.sup.2+] conductivity of both [Ca.sub.v]1.1[[alpha].sub.1S] isoforms is a common trait of all higher teleosts. This non-[Ca.sup.2+] conductivity of [Ca.sub.v]1.1 positions teleosts at the most-derived position of an evolutionary trajectory. Though EC coupling in early chordate muscles is activated by the influx of extracellular [Ca.sup.2+], it evolved toward [Ca.sub.v]1.1-RyR1 protein--protein interaction with a relatively small and slow influx of external [Ca.sup.2+] in tetrapods. Finally, the [Ca.sub.v]1.1 [Ca.sup.2+] influx was completely eliminated in higher teleost fishes. calcium conductivity | evolution | ion channels | slow and fast muscle | zebrafish www.pnas.org/cgi/doi/10.1073/pnas.0912153107

The purpose of the present study was to examine the linearity and reliability of the mechanomyographic (MMG) amplitude versus concentric dynamic constant external resistance (DCER) relationships for the bench press exercise. Twenty-one resistance-trained men (mean [+ or -] SD age = 23.5 [+ or -] 2.7 yr; 1 repetition maximum [1RM] bench press = 125.4 [+ or -] 18.4 kg) volunteered to perform submaximal bench press muscle actions as explosively as possible from 10% to 90% of the 1 RM on 2 separate occasions. During each muscle action, surface MMG signals were detected from both the right and left pectoralis major and triceps brachii, and the concentric portion of the range of motion was selected for analysis. The coefficients of determination for the MMG amplitude versus concentric DCER relationships ranged from [r.sup.2] = 0.010 to 0.980 for the right pectoralis major, [r.sup.2] = 0.010 to 0.943 for the left pectoralis major, [r.sup.2] = 0.010 to 0.920 for the right triceps brachii, and [r.sup.2] = 0.020 to 0.915 for the left triceps brachii, thus indicating a wide range of linearity between subjects. The intraclass correlation coefficients (ICC) and corresponding standard error of measurements (SEM) for the linear slope coefficients for these relationships were 0.592 (39.3% of the mean value), 0.537 (41.9% of the mean value), 0.625 (42.0% of the mean value), and 0.460 (60.2% of the mean value) for the right pectoralis major, the left pectoralis major, the right triceps brachii, and the left triceps brachii, respectively. These data demonstrated that these relationships were neither linear nor reliable enough to be used for assessing issues such as the neural versus hypertrophic contributions to training-induced strength gains and the mechanisms underlying cross-education. KEY WORDS efficiency of electrical activity, mechanomyogram, intraclass correlation coefficient

We have been searching for a mechanism to induce smooth muscle contraction that is not associated with phosphorylation of the regulatory light chain (RLC) of smooth muscle myosin (Nakamura A, Xie C, Zhang Y, Gao Y, Wang HH, Ye LH, Kishi H, Okagaki T, Yoshiyama S, Hayakawa K, Ishikawa R, Kohama K. Biochem Biophys Res Commun 369: 135-143, 2008). In this article, we report that arachidonic acid (AA) stimulates ATPase activity of unphosphorylated smooth muscle myosin with maximal stimulation ([R.sub.max]) of 6.84 [+ or -] 0.51 relative to stimulation by the vehicle and with a half-maximal effective concentration ([EC.sub.50]) of 50.3 [+ or -] 4.2 [micro]M. In the presence of actin, [R.sub.max] was 1.72 [+ or -] 0.08 and [EC.sub.50] was 26.3 -+ 2.3 [micro]M. Our experiments with eicosanoids consisting of the AA cascade suggested that they neither stimulated nor inhibited the activity. Under conditions that did not allow RLC to be phosphorylated, AA stimulated contraction of smooth muscle tissue with an [R.sub.max] of 1.45 [+ or -] 0.07 and an [EC.sub.50] of 27.0 +- 4.4 ~M. In addition to the ATPase activities of the myosin, AA stimulated those of heavy meromyosin, subfragment 1 (S 1), S 1 from which the RLC was removed, and a recombinant heavy chain consisting of the myosin head. The stimulatory effects of AA on these preparations were about twofold. The site of AA action was indicated to be the step-releasing inorganic phosphate (P0 from the reaction intermediate of the myosin-ADP-[P.sub.i] complex. The enhancement of [P.sub.i] release by AA was supported by computer simulation indicating that AA docked in the actin-binding cleft of the myosin motor domain. The stimulatory effect of AA was detectable with both unphosphorylated myosin and the myosin in which RLC was fully phosphorylated. The AA effect on both myosin forms was suggested to cause excess contraction such as vasospasm. skinned fiber doi: 10.1152/ajpheart.00577.2009