Simultaneous measurement of membrane potential, cytosolic Ca2+, and tension in intact smooth muscles.
Microelectrode techniques and the fluorescent Ca2+ indicator indo-1 were used to measure membrane potential, cytosolic Ca2+ ([Ca2+]cyt), and muscle tension simultaneously in canine antral smooth muscles. Responses of muscles from the myenteric and submucosal regions were compared, since electrical activity and excitation-contraction coupling in these regions differ. The upstroke phase of electrical slow waves in both regions induced an increase in [Ca2+]cyt. In myenteric muscles the plateau phase of slow waves often caused either a further rise in [Ca2+]cyt or maintenance of the level reached during the upstroke event. In submucosal muscles, the plateau phase was significantly smaller and did not induce a second phase in the Ca2+ transient. Contractions were related to the amplitudes of Ca2+ transients. Acetylcholine (ACh; 3 x 10(-8)-10(-6) M) increased the amplitude and duration of the plateau phase of slow waves in a concentration-dependent manner. ACh also increased the second phase of Ca2+ transients and contractile responses associated with the plateau potential. In submucosal muscles ACh induced a significant increase in the plateau phase of the slow wave and increased the corresponding phase of Ca2+ transient. Nicardipine (10(-6) M) inhibited plateau phase of slow waves and the associated increases in [Ca2+]cyt and muscle tension. BAY K 8644 (10(-7) M) augmented the plateau potential and increased [Ca2+]cyt and muscle tension. These results suggest that dihydropyridine-sensitive Ca2+ currents participate in the plateau potential. Cholinergic stimulation modulates [Ca2+]cyt and therefore force by regulating the amount of Ca2+ entering cells through these channels.
Ozaki
H
H
Department of Physiology, University of Nevada School of Medicine, Reno 89557.
Stevens
R J
RJ
Blondfield
D P
DP
Publicover
N G
NG
Sanders
K M
KM
D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology; D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D004285:Dogs; D004533:Egtazic Acid / Q000494:pharmacology; D004594:Electrophysiology / Q000295:instrumentation / Q000379:methods; D005260:Female; D066298:In Vitro Techniques; D015759:Ionomycin / Q000494:pharmacology; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects / Q000502:physiology*; D009529:Nicardipine / Q000494:pharmacology; D013270:Stomach / Q000187:drug effects / Q000502:physiology*
D004533:Egtazic Acid; D015759:Ionomycin; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; D009529:Nicardipine; D000109:Acetylcholine; D002118:Calcium