Effect of membrane potential on the initiation of acetylcholine-induced Ca2+ transients in isolated guinea pig coronary myocytes.
The muscarinic stimulation of single voltage-clamped coronary arterial smooth muscle cells of the guinea pig was used to evaluate the effect of membrane potential on the inositol 1,4,5-tris-phosphate (IP3)-mediated changes of ionized [Ca2+] in the cytoplasm (Ca2+ transient) measured with indo 1. When applied at the membrane potential of -50 mV, 10 micromol/L acetylcholine (ACh) induced a [Ca2+]i increase after the mean latency of 2.6+/-0.9 s. The latency was reduced to 1.1 +/- 0.3 s when the same dose was applied at a holding potential of +50 mV. In paired experiments in the same cells, the latency of response at +50 mV was reduced by a factor of 2.2 +/- 0.3 compared with the response at -50 mV. Supramaximal [ACh] (100 micromol/L) induced Ca2+ transients with a 0.4 +/- 0.1-s latency, which was independent of membrane potential. When applied repetitively at -50 mV, ACh induced Ca2+ transients with a progressively reduced amplitude and slower rate of rise. Depolarization to +50 mV accelerated the rate of rise of the Ca2+ transient by a factor of 3.4 +/- 0.4 without affecting the amplitude. The modulation of the initiation of Ca2+ transient by a 100-mV depolarization can be explained by an approximately threefold increase in the rate of IP3 accumulation.
Ganitkevich
V Y
VY
Department of Physiology, University of Cologne, Germany.
Isenberg
G
G
D000109:Acetylcholine / Q000494:pharmacology*; D000818:Animals; D001158:Arteries / Q000166:cytology / Q000502:physiology; D002118:Calcium / Q000502:physiology*; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology*; D002469:Cell Separation; D003331:Coronary Vessels / Q000166:cytology / Q000502:physiology*; D004594:Electrophysiology; D006168:Guinea Pigs; D008564:Membrane Potentials; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000502:physiology*; D009994:Osmolar Concentration
D015220:Calcium Channels; D000109:Acetylcholine; D002118:Calcium