Regulation of calcium current by voltage and cytoplasmic calcium in canine gastric smooth muscle.
The regulation of Ca2+ current by intracellular Ca2+ was studied in isolated myocytes from the circular layer of canine gastric antrum. Ca2+ current was measured with the whole cell patch-clamp technique, and changes in cytoplasmic Ca2+ ([Ca2+]i) were simultaneously measured with indo-1 fluorescence. Ca2+ currents were activated by depolarization and inactivated despite maintained depolarization. Ca2+ current inactivation was fit with a double exponential function. Using Ba2+ or Na+ as charge carriers removed the fast component of inactivation, whereas enhanced intracellular buffering of Ca2+ did not remove the fast component. Ca2+ currents were associated with a rise in [Ca2+]i. The decrease in [Ca2+]i following repolarization was exponential, and during the relaxation of [Ca2+]i, Ca2+ current was inactivated. The inward current recovered with a similar time course as the decrease in [Ca2+]i, suggesting that [Ca2+]i regulates the basal availability of Ca2+ channels. These data support the hypothesis that, although [Ca2+]i may influence the resting level of inactivation, it is the "submembrane" compartment of [Ca2+]i that regulates the development of inactivation.
Vogalis
F
F
Department of Physiology, University of Nevada School of Medicine, Reno 89557.
Publicover
N G
NG
Sanders
K M
KM
D000818:Animals; D001464:Barium / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000502:physiology*; D003593:Cytoplasm / Q000378:metabolism; D004285:Dogs; D004533:Egtazic Acid / Q000494:pharmacology; D005260:Female; D005456:Fluorescent Dyes; D066298:In Vitro Techniques; D007211:Indoles; D007700:Kinetics; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D009130:Muscle, Smooth / Q000502:physiology*; D011706:Pyloric Antrum / Q000502:physiology*; D013997:Time Factors
D015220:Calcium Channels; D005456:Fluorescent Dyes; D007211:Indoles; D001464:Barium; D004533:Egtazic Acid; C048960:indo-1; D002118:Calcium