Effects of nifedipine on contraction by Mn2+ in Ca2+-free, high-K+ medium in ileal longitudinal muscle.
1. The tension development due to 5 mM Mn2+ in Ca2+-free medium was dependent on the external K+ concentration above 35 mM in ileal muscle. 2. Nifedipine, an L-type Ca2+ channel blocker, dose dependently inhibited both the contraction and the manganese uptake by the application of 5 mM Mn2+ in the Ca2+-free, 35-60 mM K+ medium. 3. These results suggest that Mn2+ is entering through voltage-dependent Ca2+ channels depending on ileal membrane depolarization, and it directly activates the contractile protein.
Nasu
T
T
Department of Veterinary Pharmacology, Faculty of Agriculture, Yamaguchi University, Japan. nasu@agr.yamaguchi-u.ac.jp
Shibata
A
A
Shibata
H
H
D000818:Animals; D002118:Calcium / Q000172:deficiency*; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D006168:Guinea Pigs; D007082:Ileum / Q000187:drug effects; D066298:In Vitro Techniques; D008297:Male; D008345:Manganese / Q000494:pharmacology*; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects*; D009543:Nifedipine / Q000494:pharmacology*; D011188:Potassium / Q000494:pharmacology*
D002121:Calcium Channel Blockers; D008345:Manganese; D009543:Nifedipine; D011188:Potassium; D002118:Calcium