The impact of extracellular and intracellular Ca2+ on ethanol-induced smooth muscle contraction
AbstractAim:To evaluate the impact of extracellular and intracellular Ca2+ on contractions induced by ethanol in smooth muscle.Methods:Longitudinal smooth muscle strips were prepared from the gastric fundi of mice. The contractions of smooth muscle strips were recorded with an isometric force displacement transducer.Results:Ethanol (164 mmol/L) produced reproducible contractions in isolated gastric fundal strips of mice. Although lidocaine (50 and 100 μmol/L), a local anesthetic agent, and hexamethonium (100 and 500 μmol/L), a ganglionic blocking agent, failed to affect these contractions, verapamil (1–50 μmol/L) and nifedipine (1–50 μmol/L), selective blockers of L-type Ca2+ channels, significantly inhibited the contractile responses of ethanol. Using a Ca2+-free medium nearly eliminated these contractions in the same tissue. Ryanodine (1–50 μmol/L) and ruthenium red (10–100 μmol/L), selective blockers of intracellular Ca2+ channels/ryanodine receptors; cyclopiazonic acid (CPA; 1–10 μmol/L), a selective inhibitor of sarcoplasmic reticulum (SR) Ca2+-ATPase; and caffeine (0.5–5 mmol/L), a depleting agent of intracellular Ca2+ stores, significantly inhibited the contractile responses induced by ethanol. In addition, the combination of caffeine (5 mmol/L) plus CPA (10 μmol/L), and ryanodine (10 μmol/L) plus CPA (10 μmol/L), caused further inhibition of contractions in response to ethanol. This inhibition was significantly different from those associated with caffeine, ryanodine or CPA. Furthermore the combination of caffeine (5 mmol/L), ryanodine (10 μmol/L) and CPA(10 μmol/L) eliminated the contractions induced by ethanol in isolated gastric fundal strips of mice.Conclusion:Both extracellular and intracellular Ca2+ may have important roles in regulating contractions induced by ethanol in the mouse gastric fundus.