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The role of caveolins, signature proteins of caveolae, in arterial [Ca.sup.2+] regulation is unknown. We investigated modulation of [Ca.sup.2+] homeostasis by caveolin-1 and caveolin-3 using smooth muscle cells from rat cerebral resistance arteries. Membrane current and [Ca.sup.2+] transients were simultaneously measured with voltage-clamped single cells. Membrane depolarization triggered [Ca.sup.2+] current and increased intracellular [Ca.sup.2+] concentration ([[Ca.sup.2+]].sub.i]). After repolarization, elevated [[Ca.sup.2+]].sub.i] returned to the resting level. [Ca.sup.2+] removal rate was determined from the declining phase of the [Ca.sup.2+] transient. Application of caveolin-1 antibody or caveolin-1 scaffolding domain peptide, corresponding to amino acid residues 82-101 of caveolin-1, significantly slowed [Ca.sup.2+] removal rate at a measured [[Ca.sup.2+]].sub.i] of 250 nM, with little effect at a measured [[Ca.sup.2+]].sub.i] of 600 nM. Application of caveolin-3 antibody or caveolin-3 scaffolding domain peptide, corresponding to amino acid residues 55-74 of caveolin-3, also significantly slowed [Ca.sup.2+] removal rate at a measured [[Ca.sup.2+]].sub.i] of 250 nM, with little effect at a measured [[[Ca.sup.2+]].sub.i] of 600 nM. Likewise, application of calmodulin inhibitory peptide, autocamtide-2-related inhibitory peptide, and cyclosporine A, inhibitors for calmodulin, [Ca.sup.2+]/calmodulin-dependent protein kinase II, and calcineurin, also significantly inhibited [Ca.sup.2+] removal rate at a measured [[Ca.sup.2+]].sub.i] of 250 nM but not at 600 nM. Application of cyclopiazonic acid, a sarcoplasmic reticulum [Ca.sup.2+] ATPase inhibitor, also significantly inhibited [Ca.sup.2+] removal rate at a measured [[Ca.sup.2+]].sub.i] of 250 nM but not at 600 nM. Our results suggest that caveolin-1 and caveolin-3 are important in [Ca.sup.2+] removal of resistance artery smooth muscle cells. caveolin-1 scaffolding domain peptide; caveolin-3 scaffolding domain peptide; calmodulin; calcium/calmodulin-dependent protein kinase II; calcineurin doi:10.1152/ajpheart.00669.2006

Phosphorylation of the 20-kDa regulatory myosin light chain (MLC) of smooth muscle is known to cause monomeric myosins in solution to self-assemble into thick filaments. The role of MLC phosphorylation in thick filament formation in intact muscle, however, is not clear. It is not known whether the phosphorylation is necessary to initiate thick filament assembly in vivo. Here we show, by using a potent inhibitor of MLC kinase (wortmannin), that the MLC phosphorylation and isometric force in trachealis muscle could be abolished without affecting calcium transients. By measuring cross-sectional densities of the thick filaments electron microscopically, we also show that inhibition of MLC phosphorylation alone did not cause disassembly of the filaments. The unphosphorylated thick filaments, however, partially dissolved when the muscle was subjected to oscillatory strains (which caused a 25% decrease in the thick filament density). The postoscillation filament density recovered to the preoscillation level only when wortmannin was removed and the muscle was stimulated. The data suggest that in vivo thick filament reassembly after mechanical perturbation is facilitated by the cyclic MLC phosphorylation associated with repeated stimulation. airway smooth muscle; contraction; ultrastructure; biochemistry; calcium transients

Author(s): T. Burdyga; Susan Wray Nature 436, 559-562 (2005) The panels of Fig. 3 in this Letter are incorrectly cited in the text. In the first full paragraph on page [...]

2- and 3-dimensional confocal imaging of Fluo-4 loaded ureteric microvesells in situ allowed us to demonstrate distinct morphology, Ca2+ signalling and contractility in myocytes of arcade arterioles and pericytes of arcade venules. In myocytes and pericytes, Ca2+ signals arise exclusively from Ca2+ release from the sarcoplasmic reticulum through inositol 1,4,5-trisphosphate receptors. Ca2+ transients in pericytes are less oscillatory, slower and longer-lasting than those in myocytes. The data obtained suggest differences in the mechanisms controlling local blood flow in precapillary arterioles and postcapillary venules. [ABSTRACT FROM AUTHOR]

Abstract: In endothelial cells there remain uncertainties in the details of how Ca2+ signals are generated and maintained, especially in intact preparations. In particular the role of the sarco-endoplasmic reticulum Ca2+-ATPase (SERCA), in contributing to the components of agonist-induced signals is unclear. The aim of this work was to increase understanding of the detailed mechanism of Ca2+ signalling in endothelial cells using real time confocal imaging of Fluo-4 loaded intact rat tail arteries in response to muscarinic stimulation. In particular we have focused on the role of SERCA, and its interplay with capacitative Ca2+ entry (CCE) and ER Ca2+ release and uptake. We have determined its contribution to the Ca2+ signal and how it varies with different physiological stimuli, including single and repeated carbachol applications and brief and prolonged exposures. In agreement with previous work, carbachol stimulated a rise in intracellular Ca2+ in the endothelial cells, consisting of a rapid initial phase, then a plateau upon which oscillations of Ca2+ were superimposed, followed by a decline to basal Ca2+ levels upon carbachol removal. Our data support the following conclusions: (i) the size (amplitude and duration) of the Ca2+ spike and early oscillations are limited by SERCA activity, thus both are increased if SERCA is inhibited. (ii) SERCA activity is such that brief applications of carbachol do not trigger CCE, presumably because the fall in luminal Ca2+ is not sufficient to trigger it. However, longer applications sufficient to deplete the ER or even partial SERCA inhibition stimulate CCE. (iii) Ca2+ entry occurs via STIM-mediated CCE and SERCA contributes to the cessation of CCE. In conclusion our data show how SERCA function is crucial to shaping endothelial cell Ca signals and its dynamic interplay with both CCE and ER Ca releases. [Copyright &y& Elsevier]

Abstract: Recent studies have highlighted the role of the sarcoplasmic reticulum (SR) in controlling excitability, Ca2+ signalling and contractility in smooth muscle. Caffeine, an agonist of ryanodine receptors (RyRs) on the SR has been previously shown to effect Ca2+ signalling but its effects on excitability and contractility are not so clear. We have studied the effects of low concentration of caffeine (1mM) on Ca2+ signalling, action potential and contractility of guinea pig ureteric smooth muscle. Caffeine produced reversible inhibition of the action potentials, Ca2+ transients and phasic contractions evoked by electrical stimulation. It had no effect on the inward Ca2+ current or Ca2+ transient but increased the amplitude and the frequency of spontaneous transient outward currents (STOCs) in voltage clamped ureteric myocytes, suggesting Ca2+-activated K+ channels (BK) are affected by it. In isolated cells and cells in situ caffeine produced an increase in the frequency and the amplitude of Ca2+ sparks as well the number of spark discharging sites per cell. Inhibition of Ca2+ sparks by ryanodine (50μM) or SR Ca2+-ATPase (SERCA) cyclopiazonic acid (CPA, 20μM) or BKCa channels by iberiotoxin (200nM) or TEA (1mM), fully reversed the inhibitory effect of caffeine on Ca2+ transients and force evoked by electrical field stimulation (EFS). These data suggest that the inhibitory effect of caffeine on the action potential, Ca2+ transients and force in ureteric smooth muscle is caused by activation of Ca2+ sparks/STOCs coupling mechanism. [Copyright &y& Elsevier]

The role of caveolins, signature proteins of caveolae, in arterial Ca2+ regulation is unknown. We investigated modulation of Ca2+ homeostasis by caveolin-1 and caveolin-3 using smooth muscle cells from rat cerebral resistance arteries. Membrane current and Ca2+ transients were simultaneously measured with voltage-clamped single cells. Membrane depolarization triggered Ca2+ current and increased intracellular Ca2+ concentration ([Ca2+]i). After repolarization, elevated [Ca2+]i returned to the resting level. Ca2+ removal rate was determined from the declining phase of the Ca2+ transient. Application of caveolin-1 antibody or caveolin-1 scaffolding domain peptide, corresponding to amino acid residues 82-101 of caveolin-1, significantly slowed Ca2+ removal rate at a measured [Ca2+]i of 250 nM, with little effect at a measured [Ca2+]i of 600 nM. Application of caveolin-3 antibody or caveolin-3 scaffolding domain peptide, corresponding to amino acid residues 55-74 of caveolin-3, also significantly slowed Ca2+ removal rate at a measured [Ca2+]i of 250 nM, with little effect at a measured [Ca2+]i of 600 nM. Likewise, application of calmodulin inhibitory peptide, autocamtide-2-related inhibitory peptide, and cyclosporine A, inhibitors for calmodulin, Ca2+/calmodulin-dependent protein kinase II, and calcineurin, also significantly inhibited Ca2+ removal rate at a measured [Ca2+]i of 250 nM but not at 600 nM. Application of cyclopiazonic acid, a sarcoplasmic reticulum Ca2+ ATPase inhibitor, also significantly inhibited Ca2+ removal rate at a measured [Ca2+]i of 250 nM but not at 600 nM. Our results suggest that caveolin-1 and caveolin-3 are important in Ca2+ removal of resistance artery smooth muscle cells. [ABSTRACT FROM AUTHOR]

Recent data have shown Ca2+-dependent activation of Rho-kinase by sustained depolarization of arterial smooth muscle. Visceral smooth muscles, however, contract phasically in response to action potentials and it is unclear whether Ca2+-dependent or -independent Rho-kinase activation occurs. We have therefore investigated this, under physiologically relevant conditions, in intact ureter. Action potentials, ionic currents, Ca2+ transients, myosin light chain (MLC) phosphorylation and phasic contraction evoked by action potentials in guinea-pig and rat ureter were investigated. In rat, but not guinea-pig ureter, three Rho-kinase inhibitors, Y-27632, HA-1077 and H-1152, significantly decreased phasic contractions and Ca2+ transients. Voltage- and current-clamp data showed that Rho-kinase inhibition reduced the plateau component of the action potential, inhibited Ca2+-channels and, indirectly, Ca2+-activated Cl- channels. The Ca2+ channel agonist Bay K8644 could reverse these effects. The K+ channel blocker TEA could also reverse the inhibitory effect of Y-27632 on the action potential and Ca2+ transient. Ca2+ transients and inward current, activated by carbachol-induced sarcoplasmic reticulum Ca2+ release, were not affected by Rho-kinase inhibition. Rho-kinase inhibition produced a Ca2+-independent increase in the relaxation rate of contraction, associated with acceleration of MLC dephosphorylation, which was sensitive to calyculin A. These data show for the first time that: (1) Rho-kinase has major effects on Ca2+ signalling associated with the action potential, (2) this effect is species dependent and (3) Rho-kinase controls relaxation of phasic contraction of myogenic origin. Thus Rho-kinase can modulate phasic smooth muscle in the absence of agonist, and the mechanisms are both Ca2+-dependent,... [ABSTRACT FROM AUTHOR]

Objective:To characterize the contractile responses of mouse myometrium, the associated calcium (Ca2+) changes and the role of the sarcoplasmic reticulum (SR), and to better understand excitation contraction coupling in this tissue.Methods:Strips of longitudinal myometrium were used, and Ca2+ was measured after loading with Indo-1.Results:Intracellular Ca2+ transients, produced by Ca2+ entry, preceded phasic spontaneous contractions. Depolarization with high potassium concentration significantly increased the amplitude of the contractions and transformed the pattern of activity from phasic to tonic, with accompanying changes in intracellular Ca2+ concentration ([Ca2+]i). Oxytocin significantly stimulated contractile activity and [Ca2+]i above the level occurring spontanouesly. Thus all forms of contractile activity were closely correlated with Ca2+. When the SR was emptied using a blocker of the SR calcium-adenosinetriphosphatase, cyclopiazonic acid, spontaneous Ca2+ and force transients increased greatly in frequency and amplitude. Ryanodine, a blocket of Ca2+ -induced Ca2+ release (CICR), did not impair activity. In the absence of external Ca2+, oxytocin was able to relase Ca2+ from the SR through IB3 but produced only a small increase in force, demonstrating a requirement for Ca2+ entry as part of the mechanism of agonist action.Conclusion:Mouse myometrium, (1) produces contractile activity reflecting changes in [Ca2+]i irrespective of the stimulus, (2) has a significant SR Ca2+ content releasable by agonist by not CICR, (3) has an SR acting to inhibit spontaneous activity, and (4) behaves qualitatively similarly to human and rat myometrium in major aspects of excitation contraction coupling and is therefore a useufl model tissue. [ABSTRACT FROM PUBLISHER]

Our understanding of the control and effects of intracellular [Na+] ([Na+]i) in intact smooth muscle is limited by the lack of data concerning [Na+]i. The initial aim of this work was therefore to investigate the suitability of using the Na+-sensitive fluorophore SBFI in intact smooth muscle. We find this to be a good method for measuring [Na+]i in ureteric smooth muscle. Resting [Na+]i was found to be around 10 mM and rose to 25 mM when the Na+-K+-ATPase was inhibited by ouabain. This relatively low [Na+]i in the absence of Na+-K+-ATPase suggests that other cellular processes, such as Na+-Ca2+ exchange, play a role in maintaining [Na+]i under these conditions. Simultaneous measurements of [Na+]i or [Ca2+] i and force showed that Na+-Ca2+ exchange can play a functional role in ureteric smooth muscle. We found that the greater the driving force for Na+ exit and hence Ca2+ entry, the larger the contraction. In addition the Na+-Ca2+ exchanger activity under these conditions was found to be pH sensitive: acidification reduced the contraction and concomitant changes in [Ca2+] and [Na+]i. We conclude that SBFI is a useful method for monitoring [Na] in smooth muscle and that Na+-Ca2+ exchange may play a functional role in the ureter. [ABSTRACT FROM AUTHOR]