Myosin light chain phosphorylation and Mn2+-dependent acetylcholine-induced contractions in guinea pig vas deferens.
We have reported that noradrenaline but not K+ induced a sustained and dose-dependent contraction without extracellular Ca2+ and Mn2+ in Ca2+-depleted Mn2+loaded vas deferens from the guinea pig. The Mn2+dependent noradrenaline-induced contractions developed without an increase in phosphorylation of 20-kDa myosin light chain. To clarify whether such an unusual Mn2+dependent contraction was induced only by noradrenaline or not, we examined effects of acetylcholine on Ca2+-depleted Mn2+-loaded guinea pig vas deferens. Acetylcholine (1 microM(-1) mM) induced a sustained dose-dependent contraction without extracellular Ca2+ or Mn2+. W-7 (10 microM or 100 microM) and wortmannin (1 microM) both reduced the Mn2+dependent acetylcholine-induced contractions similarly to Ca2+-dependent acetylcholine-induced contractions in isolated vas deferens without either Ca2+ depletion or Mn2+ loading. However, the Mn2+-dependent acetylcholine-induced contractions developed without a significant increase in the phosphorylation of the myosin light chain determined by urea-glycerol polyacrylamide gel electrophoresis and immunoblotting. These results indicate that acetylcholine as well as noradrenaline induces Mn2+-dependent contraction and are consistent with our previous assumption that Mn2+ may preferentially support receptor-mediated contractions in the guinea pig isolated vas deferens. The results also suggest that the activation of myosin light chain kinase is essential for the development of Mn2+-dependent acetylcholine-induced contractions, and that Mn2+ may accelerate formation of non-phosphorylated attached cross-bridges during receptor activation.
Tsunobuchi-Ushijima
H
H
Department of Pharmacology, Faculty of Pharmaceutical Sciences, Kanazawa University, Japan. h-ushi@po2.nsknet.or.jp
Okuno
H
H
Gomi
Y
Y
D000109:Acetylcholine / Q000494:pharmacology*; D000818:Animals; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D006168:Guinea Pigs; D008297:Male; D008345:Manganese / Q000494:pharmacology*; D009119:Muscle Contraction / Q000187:drug effects*; D009130:Muscle, Smooth / Q000187:drug effects* / Q000378:metabolism; D018994:Myosin Light Chains / Q000378:metabolism*; D010766:Phosphorylation; D014649:Vas Deferens / Q000187:drug effects / Q000378:metabolism; D014665:Vasodilator Agents / Q000494:pharmacology*
D018994:Myosin Light Chains; D014665:Vasodilator Agents; D008345:Manganese; D000109:Acetylcholine