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.