Search

Even though rodents are accessible model animals, their electrophysiological properties are deeply different from those of humans, making the translation of rat studies to humans rather difficult. We compared the mechanisms of ventricular repolarization in various animal models to those of humans by measuring cardiac ventricular action potentials from ventricular papillary muscle preparations using conventional microelectrodes and applying selective inhibitors of various potassium transmembrane ion currents. Inhibition of the [I.sub.K1] current (10 [micro]mol/L barium chloride) significantly prolonged rat ventricular repolarization, but only slightly prolonged it in dogs, and did not affect it in humans. On the contrary, [I.sub.Kr] inhibition (50 nmol/L dofetilide) significantly prolonged repolarization in humans, rabbits, and dogs, but not in rats. Inhibition of the [I.sub.Kur] current (1 [micro]mol/L XEN-D0101) only prolonged rat ventricular repolarization and had no effect in humans or dogs. Inhibition of the [I.sub.Ks] (500 nmol/L HMR-1556) and [I.sub.to] currents (100 [micro]mol/L chromanol-293B) elicited similar effects in all investigated species. We conclude that dog ventricular preparations have the strongest translational value and rat ventricular preparations have the weakest translational value in cardiac electrophysiological experiments. Key words: action potential duration, ion currents, human, comparison Les rongeurs constituent des modeles chez les animaux bien accessibles, mais leurs proprietes electrophysiologiques sont bien differentes de celles des humains, ce qui rend l'application des etudes chez le rat a l'humain plutot difficile. Nous avons compare les modes d'action de la repolarisation ventriculaire dans divers modeles chez les animaux a ceux des humains par l'enregistrement de potentiels d'action dans des preparations de muscle papillaire ventriculaire a l'aide de microelectrodes classiques, de meme que de l'application d'inhibiteurs selectifs de divers canaux potassiques transmembranaires. L'inhibition du courant [I.sub.K1] (chlorure de baryum a 10 [micro]M) entrainait une prolongationmarquee de la repolarisation ventriculaire chez le rat, mais seulement une legere prolongation chez le chien, sans effet sur ce parametre chez l'humain. Inversement, l'inhibition du courant [I.sub.Kr] (dofetilide a 50 nM) entrainait une prolongation marquee chez l'humain, le lapin et le chien, mais pas chez le rat. L'inhibition du courant [I.sub.Kur] (XEN-D0101 a 1 [micro]M) prolongeait la repolarisation ventriculaire uniquement chez le rat, sans effet chez l'humain ni chez le chien. L'inhibition des courants [I.sub.Ks] (HMR-1556 a 500 nM) et [I.sub.to] (chromanol-293B a 100 [micro]M) entrainait des effets similaires chez toutes les especes etudiees. Nous en arrivons a la conclusion que les preparations canines de ventricule permettent de realiser les experiences d'electrophysiologie cardiaque les plus robustes quant a leur application chez l'humain, alors que les moins robustes sur ce plan sont celles qui sont realisees a l'aide de preparations de ventricule de rat. [Traduit par la Redaction] Mots-cles : duree du potentiel d'action, courants ioniques, humain, comparaison, Introduction The translational value of electrophysiological experiments can be largely dependent on the animal model used (Varro et al. 1993), and some mammalian hearts are more similar to the human [...]

Am J Physiol Renal Physiol 298: F12-F21, 2010. First published July 29, 2009; doi: 10.1152/ajprenal.90723.2008.--The [H.sup.+]-[K.sup.+]-ATPases are ion pumps that use the energy of ATP hydrolysis to transport protons ([H.sup.+]) in exchange for potassium ions ([K.sup.+]). These enzymes consist of a catalytic [alpha]-subunit and a regulatory [beta]-subunit. There are two catalytic subunits present in the kidney, the gastric or HK[[alpha].sub.j] isoform and the colonic or HK[[alpha].sub.2] isoform. In this review we discuss new information on the physiological function, regulation, and structure of the renal [H.sup.+]-[K.sup.+]-ATPases. Evaluation of enzymatic functions along the nephron and collecting duct and studies in HK[[alpha].sub.1] and HK[[alpha].sub.2] knockout mice suggest that the [H.sup.+]-[K.sup.+]-ATPases may function to transport ions other than protons and potassium. These reports and recent studies in mice lacking both HK[[alpha].sub.1] and HK[[alpha].sub.2] suggest important roles for the renal [H.sup.+]-[K.sup.+]-ATPases in acid/base balance as well as potassium and sodium homeostasis. Molecular modeling studies based on the crystal structure of a related enzyme have made it possible to evaluate the structures of HK[[alpha].sub.1] and HK[[alpha].sub.2] and provide a means to study the specific cation transport properties of [H.sup.+]-[K.sup.+]-ATPases. Studies to characterize the cation specificity of these enzymes under different physiological conditions are necessary to fully understand the role of the [H.sup.+]-[K.sup.+] ATPases in renal physiology. adenosine 5'-triphosphatase; potassium

Wear tolerance is important in sports turf, but the effects of nitrogen (N) and potassium (K) on wear mechanisms in perennial ryegrass (Lolium perenne L.) are unknown. The objective of this study was to evaluate wear mechanisms in response to N and K in this species. Field studies were conducted in 2006 and 2007 using five N levels (49, 147, 245, 343, and 441 kg [ha.sup.-1] [yr.sup.-1]) in combination with three rate levels of K (49, 245, and 441 kg [ha.sup.-1] [yr.sup.-1]). Wear was applied in both years using wear simulators. Ten plant characteristics were measured in field plots. Nitrogen had significant effect on wear tolerance and plant characteristics. Shoot growth accounted for as much as 94% of the variation in wear tolerance (r = -0.97, P [less than or equal to] 0.001). Tissue moisture measured as relative water content and shoot water content covaried with shoot growth. Wear injury, shoot growth rate and tissue moisture increased with increasing N, especially when fertilized in excess of 245 kg N [ha.sup.-1] [yr.sup.-1]. Tissue moisture explained as much as 66% (r = -0.81, P [less than or equal to] 0.001) of the variation in wear tolerance. Cell wall components, leaf strength, and shoot density were secondary in explaining wear tolerance. Verdure was not important. Tissue K and soil-available K were not correlated with wear tolerance. These results suggest fertilizing at no more than 245 kg N [ha.sup.-1] [y.sup.-1] to maintain optimum wear tolerance, shoot growth rate and tissue moisture. doi: 10.2135/cropsci2008.08.0474

Fertility may influence wear tolerance and recovery, but its effects on perennial ryegrass (Lolium perenne L.) are unknown. Our objective was to evaluate the effects of nitrogen (N) and potassium (K) on wear tolerance and recovery in perennial ryegrass. Field studies were conducted in 2006 and 2007 to evaluate five rate levels of N (49, 147, 245, 343, and 441 kg [ha.sup.-1] [yr.sup.-1]) with three rate levels of K (49, 245, and 441 kg [ha.sup.-1] [yr.sup.-1]). Wear was applied using differential slip wear (DSW) and grooming brush wear (GBW). Injury was assessed using visual ratings and a relative chlorophyll index from spectral readings measured on wear-treated and nontreated plots. Grooming brush wear was ineffective for assessing recovery. Wear tolerance ratings between GBW and DSW were correlated with r-values as high as 0.93 (P [less than or equal to] 0.001). Reflectance readings were correlated with GBW and DSW ratings. Nitrogen influenced wear tolerance and recovery. Wear tolerance decreased linearly as N increased, and N accounted for as much as 95% of the treatment variation. Reductions in wear tolerance with increasing K were observed with GBW, while significant gains in recovery from DSW were observed with K at 2 wk after treatment (2WAT). Nitrogen in excess of 245 kg [ha.sup.-1] [yr.sup.-1] promoted reductions in wear tolerance but faster recovery. The 245 kg N [ha.sup.-1] [yr.sup.-1] rate afforded full recovery in the shortest interval as early as 8WAT. Optimum N for maximum wear tolerance and recovery for perennial ryegrass is 245 kg N [ha.sup.-1] [yr.sup.-1] . doi: 10.2135/cropsci2008.08.0473

The Na-Cl cotransporter NCC is expressed in the distal convoluted tubule, activated by phosphorylation, and has been implicated in renal NaCl and [K.sup.+] homeostasis. The serum and glucocorticoid inducible kinase l (SGK1) contributes to renal NaCl retention and [K.sup.+] excretion, at least in part, by stimulating the epithelial [Na.sup.+] channel and [Na.sup.+]-[K.sup.+]-ATPase in the downstream segments of aldosterone-sensitive [Na.sup.+]/[K.sup.+] exchange. In this study we confirmed in wild-type mice (WT) that dietary NaCl restriction increases renal NCC expression and its phosphorylation at [Thr.sup.53], [Thr.sup.58], and [Ser.sup.71], respectively. This response, however, was attenuated in mice lacking SGK1 ([Sgk1.sup.-/-]), which may contribute to impaired NaCl retention in those mice. Total renal NCC expression and phosphorylation at [Thr.sup.53], [Thr.sup.58], and [Ser.sup.71] in WT were greater under low- compared with high-[K.sup.+] diet. This finding is consistent with a regulation of NCC to modulate [Na.sup.+] delivery to downstream segments of [Na.sup.+]/[K.sup.+] exchange, thereby modulating [K.sup.+] excretion. Dietary [K.sup.+]-dependent variation in renal expression of total NCC and phosphorylated NCC were not attenuated in [Sgk1.sup.-/-] mice. In fact, high-[K.sup.+] diet-induced NCC suppression was enhanced in [Sgk1.sup.-/-] mice. The hyperkalemia induced in [Sgk1.sup.-/-] mice by a high-[K.sup.+] diet may have augmented NCC suppression, thereby increasing [Na.sup.+] delivery and facilitating [K.sup.+] excretion in downstream segments of impaired [Na.sup.+]/[K.sup.+] exchange. In summary, changes in NaCl and [K.sup.+] intake altered NCC expression and phosphorylation, an observation consistent with a role of NCC in NaCl and [K.sup.+] homeostasis. The two maneuvers dissociated plasma aldosterone levels from NCC expression and phosphorylation, implicating additional regulators. Regulation of NCC expression and phosphorylation by dietary NaCl restriction appears to involve SGK1. with-no-lysine kinases; diuretic; epithelial sodium channel; intake; sodium chloride

Cardiac [Na.sup.+]-[K.sup.+]-ATPase (NKA) regulates intracellular [Na.sup.+], which in turn affects intracellular [Ca.sup.2+] and contractility via the [Na.sup.+]/[Ca.sup.2+] exchanger. Extracellular [K.sup.+] concentration ([[K.sup.+]]) is a central regulator of NKA activity. Phospholemman (PLM) has recently been recognized as a critical regulator of NKA in the heart. PLM reduces the intracellular [Na.sup.+] affinity of NKA, an effect relieved by PLM phosphorylation. Here we tested whether the NKA [[alpha].sub.1]-vs. [[alpha].sub.2]-isoforms have different external [K.sup.+] sensitivity and whether PLM and PKA activation affects the NKA affinity for [K.sup.+] in mouse cardiac myocytes. We measured the external [[K.sup.+]] dependence of the pump current generated by the ouabain resistant NKA isoform in myocytes from wild-type (WT) mice (i.e., current due to NKA-[[alpha].sub.1]) and mice in which the NKA isoforms have swapped ouabain affinities ([[alpha].sub.1] is ouabain sensitive and [[alpha].sub.2] is ouabain resistant) to assess current due to NKA-[[alpha].sub.2]. We found that NKA-[[alpha].sub.1] has a higher affinity for external [K.sup.+] than NKA-[[alpha].sub.2] [half-maximal pump activation ([K.sub.0.5]) = 1.5 [+ or -] 0.1 vs. 2.9 [+ or -] 0.3 mM]. The apparent external [K.sup.+] affinity of NKA was significantly lower in myocytes from WT vs. PLM-knockout mice ([K.sub.0.5] = 2.0 [+ or -] 0.2 vs. 1.05 [+ or -] 0.08 mM). However, PKA activation by isoproterenol (1 [micro]M) did not alter the [K.sub.0.5] of NKA for external [K.sup.+] in WT myocytes. We conclude that 1) NKA-[[alpha].sub.1] has higher affinity for [K.sup.+] than NKA-[[alpha].sub.2] in cardiac myocytes, 2) PLM decreases the apparent external [K.sup.+] affinity of NKA, and 3) phosphorylation of PLM at the cytosolic domain does not alter apparent extracellular [K.sup.+] affinity of NKA. voltage-clamp; phosphorylation

The gene for the Thermotoga maritima Trk potassium transporter component TrkA was originally thought to be a frameshift mutation and not to encode a functional protein. However, expression from this gene yielded a complex consisting of two distinct proteins designated TM1088A and -B. Genetic complementation of Escherichia coli mutants unable to transport potassium suggests that TM1088A/B is part of a functional Trk potassium transporter complex with the membrane protein TM1089. The protein structure for TM1088A shows a characteristic Rossmann fold indicating an [NAD.sup.+] binding site and has structural similarity to potassium channel-related proteins. Ligand binding studies indicated that ATP, ADP, and AMP stabilized TM1088A to a much greater degree than NADH and NAD, consistent with the crystal structure of TM1088A, which contains a bound AMP natural ligand at the characteristic GXGXXG nucleotide binding site. Mutation of single and all glycines at this nucleotide binding site eliminated in vitro protein stabilization by the ligand, yet these mutated proteins could still functionally complement the E. coli potassium uptake mutants. We predict that this new two-subunit class of TrkA proteins is present in a number of organisms. A further subclass of the predicted two-subunit TrkA proteins lack an identifiable membrane-spanning subunit of the Trk [K.sup.+] transporter. This class, as exemplified by Mycobacterium tuberculosis, did not complement E. coli potassium transport with the native E. coil TrkH; thus, it may require a novel TrkH-like protein for activity or provide an alternate function in vivo.

In the presence of aldosterone, plasma sodium in the high physiological range stiffens endothelial cells and reduces the release of nitric oxide. We now demonstrate effects of extracellular potassium on stiffness of individual cultured bovine aortic endothelial cells by using the tip of an atomic force microscope as a mechanical nanosensor. An acute increase of potassium in the physiological range swells and softens the endothelial cell and increases the release of nitric oxide. A high physiological sodium concentration, in the presence of aldosterone, prevents these changes. We propose that the potassium effects are caused by submembranous cortical fluidization because cortical actin depolymerization induced by cytochalasin D mimics the effect of high potassium. In contrast, a low dose of trypsin, known to activate sodium influx through epithelial sodium channels, stiffens the submembranous cell cortex. Obviously, the cortical actin cytoskeleton switches from gelation to solation depending on the ambient sodium and potassium concentrations, whereas the center of the cell is not involved. Such a mechanism would control endothelial deformability and nitric oxide release, and thus influence systemic blood pressure. aldosterone | blood pressure cortical actin | epithelial sodium channel | stiffness

Excitation of muscle often leads to a net loss of cellular [K.sup.+] and a rise in extracellular [K.sup.+] ([ [[K.sup.+] ] .sub.o)], which in turn inhibits excitability and contractility. It is important, therefore, to determine how this [K.sup.+] is cleared by diffusion into the surroundings or by reaccumulation into the muscle cells. The inhibitory effects of the rise in [[[K.sup.+]].sub.o] may be assessed from the time course of changes in tetanic force in isolated muscles where diffusional clearance of [K.sup.+] is eliminated by removing the incubation medium and allowing the muscles to contract in air. Measurements of tetanic force, endurance, and force recovery showed that in rat soleus and extensor digitorum longus (EDL) muscles there was no significant difference between the performance of muscles contracting in buffer or in air for up to 8 min. Ouabain-induced inhibition of [K.sup.+] clearance via the [Na.sup.+],[K.sup.+] pumps markedly reduced contractile endurance and force recovery in air. Incubation in buffer containing 10 mM [K.sup.+] clearly inhibited force development and endurance, and these effects were considerably reduced by stimulating [Na.sup.+],[K.sup.+] pumps with the [beta]2-agonist salbutamol. Following 30-60 s of continuous stimulation at 60 Hz, the amount of [K.sup.+] released into the extracellular space was assessed from washout experiments. The release of intracellular [K.sup.+] per pulse was fourfold larger in EDL than in soleus, and in the two muscles, the average [[[K.sup.+]].sub.o] reached 52.4 and 26.0 mM, respectively, appreciably higher than previously detected. In conclusion, prevention of diffusion of [K.sup.+] from the extracellular space of isolated working muscles causes only modest interference with contractile performance. The [Na.sup.+],[K.sup.+] pumps play a major role in the clearance of [K.sup.+] and the maintenance of force. This new information is important for the evaluation of [K.sup.+]-induced inhibition in muscles, where diffusional clearance of [K.sup.+] is reduced by tension development sufficient to suppress circulation.

A whole body skeletal muscle [(SM); kg] mass estimation model, based on total body potassium [(TBK); mmol] measured by whole body [sup.40]K] counting (WBC) was developed (SM = 0.0082*TBK) and validated in adults in a previous study. It is unknown whether the adult TBK SM prediction model is applicable for pediatric use. The aim of this study was to derive and validate a pediatric TBK SM prediction equation. SM measured by MRI was used as the criterion and TBK was measured by WBC. The protocol was completed in 116 healthy children, 66 males and 50 females, 11.7 [+ or -] 3.5 y (mean [+ or -] SD, range = 5-17 y). A strong linear correlation was observed between TBK and SM (r = 0.984; P < 0.001). The SM:TBK ratio was 0.0071 [+ or -] 0.0008 kg/mmol in the children studied, much lower than the corresponding value of 0.0082 kg/mmol in adults. An empirical SM prediction equation was developed using TBK alone: SM = 0.0085.TBK- 2.83, [r.sup.2] = 0.97, SEE = 1.39 kg. Bland-Altman analysis did not disclose a significant bias in the prediction of SM. When biological factors entered along with TBK in the general linear model, another prediction equation was developed: SM = 5.52 + 0.001*TBK (mmol) + 0.081-weight (kg) - 0.049.height (cm) + 0.00004*TBK * height + race (-0.60 for Caucasian, 0.49 for African-American, and 0 for Hispanic). Because the adult TBK SM prediction model is not applicable for pediatric use, this study provides new empirical TBK SM prediction equations that should prove useful for studies on nutrition, growth, and development in children.

A Western-type diet is associated with osteoporosis and calcium nephrolithiasis. On the basis of observations that calcium retention and inhibition of bone resorption result from alkali administration, it is assumed that the acid load inherent in this diet is responsible for increased bone resorption and calcium loss from bone. However, it is not known whether the dietary acid load acts directly or indirectly (i.e., via endocrine changes) on bone metabolism. It is also unclear whether alkali administration affects bone resorption/calcium balance directly or whether alkali-induced calcium retention is dependent on the cation (i.e., potassium) supplied with administered base. The effects of neutralization of dietary acid load (equimolar amounts of NaHC[O.sub.3] and KHC[O.sub.3] substituted for NaCl and KCl) in nine healthy subjects (6 men, 3 women) under metabolic balance conditions on calcium balance, bone markers, and endocrine systems relevant to bone [glucocorticoid secretion, IGF-1, parathyroid hormone (PTH)/1,25[(OH).sub.2] vitamin D and thyroid hormones] were studied. Neutralization for 7 days induced a significant cumulative calcium retention (10.7 [+ or -] 0.4 mmol) and significantly reduced the urinary excretion of deoxypyridinoline, pyridinoline, and n-telopeptide. Mean daily plasma cortisol decreased from 264 [+ or -] 45 to 232 [+ or -] 43 nmol/l (P = 0.032), and urinary excretion of tetrahydrocortisol (THF) decreased from 2,410 [+ or -] 210 to 2,098 [+ or -] 190 [micro]g/24 h (P = 0.027). No significant effect was found on free IGF-1, PTH/1,25[(OH).sub.2] vitamin D, or thyroid hormones. An acidogenic Western diet results in mild metabolic acidosis in association with a state of cortisol excess, altered divalent ion metabolism, and increased bone resorptive indices. Acidosis-induced increases in cortisol secretion and plasma concentration may play a role in mild acidosis-induced alterations in bone metabolism and possibly in osteoporosis associated with an acidogenic Western diet. glucocorticoid; acid-base; potassium; acidosis; osteoporosis

The effects of 0.3-10 nM extracellular protons (pH 9.5-8.0) on ouabain-sensitive rubidium influx were determined in 4,4'-diisocyanostilbene-2, 2'-disulfonate (DIDS)-treated human and rat erythrocytes. This treatment clamps the intracellular H. We found that rubidium binds much better to the protonated pump than the unprotonated pump; 13-fold better in rat and 34-fold better in human erythrocytes. This clearly shows that protons are not competing with rubidium in this proton concentration range. Bretylium and tetrapropylammonium also bind much better to the protonated pump than the unprotonated pump in human erythrocytes and in this sense they are potassium-like ions. In contrast, guanidinium and sodium bind about equally well to protonated and unprotonated pump in human red cells. In rat red cells, protons actually make sodium bind less well (about sevenfold). Thus, protons have substantially different effects on the binding of rubidium and sodium. The effect of protons on ouabain binding in rat red cells was intermediate between the effects of protons on rubidium binding and on sodium binding. Remarkably, all four cationic inhibitors (bretylium, guanidinium, sodium, and tetrapropylammonium) had similar apparent inhibitory constants for the unprotonated pump (~5-10 mM). The [K.sub.d] for proton binding to the human pump, with the empty transport site facing extracellularly is 13 nM, whereas the extracellular transport site loaded with sodium is 9.5 nM, and with rubidium is 0.38 nM. In rat red cells there is also a substantial difference in the [K.sub.d] for proton binding to the sodium-loaded pump (14.5 nM) and the rubidium-loaded pump (0.158 nM). These data suggest that important rearrangements occur at the extracellular pump surface as the pump moves between conformations in which the outward facing transport site has sodium bound, is empty, or has rubidium bound and that guanidinium is sodium-like and bretylium and tetrapropylammonium are rubidium-like. KEY WORDS: pH clamp * tetrapropylammonium * ion transport * Na(+)-K(+)-exchanging ATPase * red blood cells

We purified Histagged ROMK1 and carried out in vitro phosphorylation assays with [sup.32]P-radiolabeled ATP to determine whether ROMK1 protein is a substrate for PTK. Addition of active c-Src and [[sup.32]P]ATP to the purified ROMK1 protein resulted in the phosphorylation of the ROMK1 protein. However, c-Src did not phosphorylate R1Y337A in which tyrosine residue 337 was mutated to alanine. Furthermore, phosphopeptide mapping identified two phosphopeptides from the trypsin-digested ROMK1 protein. In contrast, no phosphorylated peptide has been found in the trypsin-digested R1Y337A protein. This suggested that two phosphorylated peptides might contain the same tyrosine residue. Also, addition of c-Src and [[sup.32]P]ATP phosphorylated the synthesized peptide corresponding to amino acid sequence 333-362 of the COOH terminus of ROMK1. We then examined the effect of dietary K intake on the tyrosine-phosphorylated ROMK level. Although the ROMK channels pulled down by immunoprecipitation with ROMK antibody were the same from rats on a K-deficient diet or on a high-K diet, more ROMK channels were phosphorylated by PTK in rats on a K-deficient diet than those on a high-K diet. We conclude that ROMK1 can be phosphorylated by PTK and that tyrosine residue 337 is the key site for the phosphorylation. Also, the tyrosine phosphorylation of ROMK is modulated by dietary K intake. This strongly suggests that PTK is an important member of the aldosterone-independent signal transduction pathway for regulating renal K secretion. renal potassium secretion; hypokalemia; dietary potassium intake; protein tyrosine phosphatase; cortical collecting duct

Pendrin is an anion exchanger in the cortical collecting duct of the mammalian nephron that appears to mediate apical [Cl.sup.-]/HC[O.sup.-.sub.3] exchange in bicarbonate-secreting intercalated cells. The goals of this study were to determine 1) if pendrin immunoreactivity was present in the gills of a euryhaline elasmobranch (Atlantic stingray, Dasyatis sabina), and 2) if branchial pendrin immunoreactivity was influenced by environmental salinity. Immunoblots detected pendrin immunoreactivity in Atlantic stingray gills; pendrin immunoreactivity was greatest in freshwater stingrays compared with freshwater stingrays acclimated to seawater (seawater acclimated) and marine stingrays. Using immunohistochemistry, pendrin-positive cells were detected on both gill lamellae and interlamellar regions of freshwater stingrays but were more restricted to interlamellar regions in seawater-acclimated and marine stingray gills. Pendrin immunolabeling in freshwater stingray gills was more apical, discrete, and intense compared with seawater-acclimated and marine stingrays. Regardless of salinity, pendrin immunoreactivity occurred on the apical region of cells rich with basolateral vacuolar-proton-ATPase, and not in [Na.sup.+]-[K.sup.+]-ATPase-rich cells. We suggest that a pendrin-like transporter may contribute to apical [Cl.sup.-]/HC[O.sup.-.sub.3] exchange in gills of Atlantic stingrays from both freshwater and marine environments. anion exchanger; vacuolar-proton-adenosinetriphosphatase; sodium-potassium-adenosinetriphosphatase; sodium chloride regulation; acid/base regulation; Dasyatis sabina

Muscular K uptake depends on skeletal muscle Na-K-ATPase concentration and activity. Reduced K uptake is observed in vitro in K-depleted rats. We evaluated skeletal muscle K clearance capacity in vivo in rats K depleted for 14 days. [[sup.3]H]ouabain binding, [[alpha].sub.1] and [[alpha].sub.2] Na-K-ATPase isoform abundance, and K, Na, and Mg content were measured in skeletal muscles. Skeletal muscle K, Na, and Mg and plasma K were measured in relation to intravenous KCl infusion that continued until animals died, i.e., maximum KCl dose was administered. In soleus, extensor digitorum longus (EDL), and gastrocnemius muscles K depletion significantly reduced K content by 18%, 15%, and 19%, [[sup.3]H]ouabain binding by 36%, 41%, and 68%, and [[alpha].sub.2] isoform abundance by 34%, 44%, and 70%, respectively. No significant change was observed in [[alpha].sub.1] isoform abundance. In EDL and gastrocnemius muscles K depletion significantly increased Na (48% and 59%) and Mg (10% and 17%) content, but only tendencies to increase were observed in soleus muscle. K-depleted rats tolerated up to a fourfold higher KCl dose. This was associated with a reduced rate of increase in plasma K and increases in soleus, EDL, and gastrocnemius muscle K of 56%, 42%, and 41%, respectively, but only tendencies to increase in controls. However, whereas K uptake was highest in K-depleted animals, the K uptake rate was highest in controls. In vivo K depletion is associated with markedly increased K tolerance and K clearance despite significantly reduced skeletal muscle Na-K-ATPase concentration. The concern of an increased risk for K intoxication during K repletion seems unwarranted. sodium-potassium-adenosinetriphosphatase; magnesium

The effect of acidosis on the electrical activity of isolated rat atrial myocytes was investigated using the patch-clamp technique. Reducing the pH of the bathing solution from 7.4 to 6.5 shortened the action potential. Acidosis had no significant effect on transient outward or inward rectifier currents but increased steady-state outward current. This increase was still present, although reduced, when intracellular [Ca.sup.2+] was buffered by 1,2-bis(2-aminophenoxy) ethane-N,N,N',N'-tetraacetic acid (BAPTA); BAPTA also inhibited acidosis-induced shortening of the action potential. [Ni.sup.2+] (5 mM) had no significant effect on the acidosis-induced shortening of the action potential. Acidosis also increased inward current at -80 mV and depolarized the resting membrane potential Acidosis activated an inwardly rectifying [Cl.sup.-] current that was blocked by 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS), which also inhibited the acidosis-induced depolarization of the resting membrane potential. It is concluded that an acidosis-induced increase in steady-state outward [K.sup.+] current underlies the shortening of the action potential and that an acidosis-induced increase in inwardly rectifying [Cl.sup.-] current underlies the depolarization of the resting membrane potential during acidosis. action potential; potassium current; chloride current; perforated patch

A history of the study of sodium pumping is presented. Evidence that cell membranes of animals have pumps that exchange sodium ions in the cell for potassium ions outside is reviewed with discussion of other aspects of this topic, including that one of the working cycle involves transfer of a phosphate group and a conformational change and that the other half does too. The phosphate transfer is associated with occlusion of ions bound at one surface and the conformational change that lets the occluded ions go on the other side. The career, education, and life of the author are discussed.

Spicer, Zachary, Lane L. Clarke, Lara R. Gawenis, and Gary E. Shull. Colonic [H.sup.+]-[K.sup.+]-ATPase in [K.sup.+] conservation and electrogenic [Na.sup.+] absorption during [Na.sup.+] restriction. Am J Physiol Gastrointest Liver Physiol 281: G1369-G1377, 2001.--Upregulation of the colonic [H.sup.+]-[K.sup.+]-ATPase (cHKA) during hyperaldosteronism suggests that it functions in both [K.sup.+] conservation and electrogenic Na+ absorption in the colon when [Na.sup.+]-conserving mechanisms are activated. To test this hypothesis, wild-type (cHK[A.sup.+/+]) and cHKA-deficient (cHK[A.sup.-/-]) mice were fed [Na.sup.+]-replete and Na+-restricted diets and their responses were analyzed. In both genotypes, [Na.sup.+] restriction led to reduced plasma [Na.sup.+] and increased serum aldosterone, and mRNAs for the epithelial [Na.sup.+] channel (ENaC) [beta]-and [gamma]-subunits, channel-inducing factor, and cHKA were increased in distal colon. Relative to wild-type controls, cHK[A.sup.-/-] mice on a [Na.sup.+]-replete diet had elevated fecal [K.sup.+] excretion. Dietary [Na.sup.+] restriction led to increased [K.sup.+] excretion in knockout but not in wild-type mice. The amiloride-sensitive, ENaC-mediated short-circuit current in distal colon was significantly reduced in knockout mice maintained on either the [Na.sup.+]-replete or [Na.sup.+]-restricted diet. These results demonstrate that cHKA plays an important role in [K.sup.+] conservation during dietary [Na.sup.+] restriction and suggest that cHKA-mediated [K.sup.+] recycling across the apical membrane is required for maximum electrogenic [Na.sup.+] absorption. Atp1al1; potassium absorption; sodium absorption; hydrogen secretion

Byline: A. S. Pivovarov (1), D. V. Boguslavskii (1) Abstract: The effects of the Na, K pump inhibitor ouabain on the depth of depression of cholinosensitivity of defensive behavior command neurons LPa2, LPa3, RPa3, and RPa2 were studied in the common snail using a cellular analog of habituation the role of intracellular Ca.sup.2+ in these effects was analyzed. Integral acetylcholine-evoked transmembrane currents (ACh currents) were recorded by two-electrode membrane voltage clamping. In one group of neurons, extracellular application of ouabain (0.1 mM) by addition to the bathing solution evoked increases in the depression of the ACh current evoked by rhythmic application of mediator (with interstimulus intervals of 1--3 min), while neurons of the other groups responded with decreases in depression. After spontaneous diffusion of the Ca.sup.2+ ion chelator BAPTA (1 mM) from the intracellular microelectrode for 60--150 min, ouabain only increased the level of depression of the ACh current. After intracellular injection of CaCl.sub.2 (100 mM), ouabain only decreased the level of depression of the ACh current. It was concluded that inhibition of the Na, K pump modifies depression of the cholinosensitivity of neurons in the cellular model of habituation. The direction of the effect depends on the basal concentration of intracellular Ca.sup.2+. Author Affiliation: (1) M. V. Lomonosov Moscow State University, Moscow Article History: Registration Date: 08/10/2004

This article examines the relationship between physical activity, potassium intake, and the loss of actively metabolizing cells in an elderly sample. Findings indicate that body cell mass is significantly correlated with physical activity levels in both men and women but is not associated with dietary potassium intake.

Byline: Y. Nako (1), Yasushi Ohki (1), Akira Harigaya (1), Takeshi Tomomasa (1), Akihiro Morikawa (1) Keywords: Key wordsaAldosterone; Mechanical ventilation; Potassium; Preterm neonate; Renal tubule; Transtubular potassium concentration gradient Abstract: To determine the postnatal changes in mineralocorticoid action on the cortical distal nephron in preterm neonates, we evaluated the transtubular potassium gradient (TTKG) and its relationship to other renal and non-renal parameters in 16 preterm neonates during the first 5 weeks of life. Preterm neonates were divided into two groups according to their gestational age: the first group (group A, n=9) had a gestational age less than 30 weeks and the second group (group B, n=7) had a gestational age over 30 weeks. TTKG in both groups increased significantly with postnatal age, and TTKG in group A was significantly lower than that in group B (P=0.0003 two-way repeated analysis of variance). TTKG in group A was significantly lower during the 2 weeks of postnatal life than that in full-term neo- nates [TTKG during 1st week (mean+-SD) 3.73+-1.32, P&lt 0.00001 during 2nd week 7.77+-3.60, P=0.0096 versus full-term neonates (n=19) 11.56+-3.23]. TTKG in group B was significantly lower only during the 1st week of life (6.55+-2.71, P=0.0013) compared with full-term neonates. Plasma aldosterone concentration did not correlate with TTKG value. Stepwise regression analysis showed that postnatal age, cortical lumen sodium concentration (CLNa), and clinical condition requiring the use of mechanical ventilation were independent variables that correlated significantly with TTKG. We postulate that the low TTKG level in preterm neonates might reflect the prematurity of renal function (early postnatal age, CLNa) and the condition(s), relating to immaturity, such as the use of mechanical ventilation. Author Affiliation: (1) Department of Pediatrics, Gunma University School of Medicine, 3-39-15 Showa-machi, Maebashi, Gunma 371, Japan Tel.: +81-27-220-8205, Fax: +81-27-220-8215, JP Article note: Received: 16 October 1998 / Revised: 8 February 1999 / Accepted: 8 February 1999

Molecular and functional evidence are presented for the expression of a protein having the properties of a cotransporter of Na+-K+-2Cl-. RT-PCR of RNA isolated from rat soleus muscle with primers to a conserved putative membrane-spanning domain resulted in a single product of predicted size. Sequencing of the product showed that it has >90% homology with known rodent NKCC1 cotransporters. Immunohistochemical detection by confocal microscopy localized the majority of expression of the protein to the muscle fibers.

Research was conducted to examine the hypothesis that the changes in intestinal contractility that accompanies inflammation of the gut are agonist specific. A comparison of the response of inflamed strips to substance P(SP), motilin, ACh and K+ as a function of time was performed. Results reveals that TNBS-induced colitis in the rabbit alters the contractile response of circular colonic smooth muscle tissue. However, the extent of the change and its time course depends on the stimulus.

Skeletal muscle releases intracellular fluid K+ to buffer the drop in extracellular fluid (ECF) K+ when K+ output exceeds input. To elucidate on the mechanism and muscle specificity of the K+ shift, rats were fed K+-deficient food for 2-10 days and two muscles at phenotypic extremes were studied: slow-twitch oxidative soleus and fast-twitch glycolytic white gatrocnemius. Findings revealed that the patterns of regulation of Na+ pump isoforms in oxidative and glycolytic muscles during K+ deprivation mediated by posttranscriptional regulation of alpha2beta1 and alpha2beta are distinct and that reductions in alpha2-isoform pools can occur early enough in both muscles to explain the shift of K+ to the ECF.

The role of the tissue kallikrein-kinin system in reducing blood pressure and in protecting the kidneys were studied in spontaneously hypertensive rats (SHR) that were given a high-potassium diet. It was observed that there was a significant reduction in the systolic blood pressure of SHR after one week on the high-potassium diet. There was also an increase in the expression of renal kallikrein and bradykinin B2 receptors. Urine, kinin, cGMP and cAMP levels were also enhanced.

Potassium fluxes in red blood cells and muscle during muscle contractions were investigated. Seven subjects were asked to perform two-legged submaximal knee-extensor exercise for 30 min. Intense arm exercise was also performed for 10 min after 10 min of leg exercise. Findings showed that contracting muscle can take up K+ through a combination of K+ and hormone activation of the Na+-K+ pump. Also, changes in red blood cell K+ concentrations during muscle contraction may be caused by water movements and not transmembrane fluxes of K+.

The effects of dietary potassium depletion on the structure and function of the H+-ATPase in the distal nephron were investigated. Bafilomycin A1, a specific H+-ATPase inhibitor, was used to measure electrogenic proton secretion during sodium blockade and to determine the effect of potassium depletion on the distribution of the proton pump in cortical collecting duct. Results showed the onset of hypokalemia due to the highly significant redistribution of the staining pattern, indicating that dietary potassium depletion induces electrogenic H+-ATPase activity in the distal tubule.

A laboratory exercise about the physiology of potassium ion (K+) balance was described and may be used by physiology teachers as a teaching tool. The exercise focused on three major elements of the K+ balance physiology: a case presentation of a diuretic-induced hypokalemia, renal handling of K+ and the total body K+ balance. The effects of diuretics on the secretion of K+ was also discussed. After conducting the exercise, an interactive discussion was held among the students to determine the extent of their acquired knowledge regarding the just concluded experiment.

A study was undertaken that characterized a tyrosine-based sequence motif in the cytoplasmic tail of the gastric proton-potassium-adenosine triphosphatase (H-K-ATPase) beta-subunit required in the targeting of the ion pump to regulate storage compartment and subsequent termination of acid secretion. A mutated form of the protein was expressed in a transgenic mice under the influence of a cytomegalovirus promoter. Results revealed that the mice expressing the mutated protein were hyperkalemic and that H-K pumps expressed in the kidney were mediated by cycles of exo- and endocytosis.

The heterologous expression system of the Xenopus laevis oocyte was used in the investigation of the influence of intracellular potassium concentration on the blocking affinity and block voltage dependence of five quaternary ammonium compounds on the internal pore of the inward-rectifier potassium channel ROMK1. Results reveal that the blocking compound's apparent affinity and the voltage dependence of this affinity is modulated by the extracellular potassium concentration.

Experiments were performed to study the reabsorption of potassium in the surface proximal convoluted tubules (PCT) of kidneys from rats. The microperfusion method with rubidium-86 as transport marker was the selected technique. The factors considered in the potassium reabsorption were convection, diffusion and active transport. Results revealed that the permeability of the PCT was not dependent on the fluid reabsorption elimination. Potassium transport permeability was adequately evaluated through effective use of the rubidium-86 as a marker.

The consequences of potassium depletion on the L-arginine-nitric oxide pathway in arterial tissues were investigated. New Zealand White rabbits were given either a control diet or a low-potassium diet for 1-3 wk. Findings revealed that a low-potassium diet increases the sensitivity to endothelium-dependent stimuli. The decrease in endothelium-dependent relaxation was apparently secondary to enhanced free radical generation, which may degrade nitric oxide.

Potassium metabolism regulation requires processes for the proper distribution between the intra- and extracellular fluid compartments and for the excretion by the kidney. Clearance and single-nephron investigations revealed that renal excretion is determined by regulated potassium secretion and potassium reabsorption, respectively, in principal and intercalated cells of the distal nephron.

Five-sixths nephrectomized rats were used in the evaluation of the effects of potassium depletion on bicarbonate reabsorption in the distal tubules left behind. The regulatory mechanism involved is also examined with the use of proton secretion inhibitors. Results reveal that potassium depletion causes a significant elevation of bicarbonate absorption among partially nephrectomized rats through the stimulation of the hydrogen-ATPase activity.