Role of Ca2+ stores in acetylcholine-induced all-or-none shortening of smooth muscle cells from guinea-pig taenia caecum.
1. We have reported previously that isolated single smooth muscle cells from guinea-pig taenia caecum respond to acetylcholine (ACh) in an all-or-none manner. 2. To clarify the roles of intracellular Ca(2+) stores in the all-or-none response of isolated smooth muscle cells from guinea-pig taenia caecum to ACh, we examined the inositol 1,4,5-trisphosphate (IP(3))-induced contractile response in Staphylococcus aureus alpha-toxin-permeabilized smooth muscle cells and the effect of depletion of intracellular Ca(2+) stores on the all-or-none response to ACh in intact smooth muscle cells. 3. alpha-Toxin-permeabilized smooth muscle cells responded to 3-30 nmol/L or 0.3-3 nmol/L IP(3) in the presence of 0.2 micromol/L Ca(2+) with 1 mmol/L EGTA or 0.1 mmol/L EGTA, respectively, in an all-or-none manner. These results suggest that Ca(2+) release induced by IP(3) is Ca(2+) dependent and is evoked in an all-or-none manner. 4. In the presence of the Ca(2+) ionophore A23187 (0.1 micromol/L) or the sarcoplasmic reticulum Ca(2+)-ATPase inhibitor cyclopiazonic acid (1 micromol/L), the shortening of intact smooth muscle cells induced by increasing concentrations of ACh showed a graded response, but not an all-or-none response. 5. In conclusion, the results suggest that Ca(2+) release from Ca(2+) stores induced by IP(3) plays an important role in the all-or-none response of intact smooth muscle cells to ACh.
Mita
Mitsuo
M
Department of Pharmacodynamics, Meiji Pharmaceutical University, Tokyo, Japan. mitsuom@my-pharm.ac.jp
Toguchi-Senrui
Natsuko
N
D000109:Acetylcholine / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002432:Cecum / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D018678:Cholinergic Agents / Q000494:pharmacology; D006168:Guinea Pigs; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects* / Q000502:physiology; D009130:Muscle, Smooth / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D032389:Myocytes, Smooth Muscle / Q000187:drug effects* / Q000502:physiology; D010539:Permeability
D018678:Cholinergic Agents; D000109:Acetylcholine; D002118:Calcium