Effects of nifedipine ryanodine and cyclopiazonic acid on tension development of ileal longitudinal muscle by manganese ions in Ca(2+)-free high-K+ medium.
1. Mn2+ (5 mM) could evoke the contraction in a Ca(2+)-free, high-K+ (60 mM) medium in ileal longitudinal muscle. Nifedipine, L-type Ca2+ channel blocker, inhibited dose-dependently both the contraction and manganese uptake in the presence of 5 mM Mn2+, in the Ca(2+)-free, high-K+ medium. 2. However, both ryanodine, Ca2+ release blocker from SR and cyclopiazonic acid, specific SR Ca(2+)-ATPase blocker, had no effects on the contractions evoked by Mn2+ and the manganese uptake in the Ca(2+)-free, high-K+ medium. 3. These results suggest that Mn2+ did not liberate Ca2+ at the storage sites during the Mn(2+)-induced contraction in Ca(2+)-free, high-K+ medium. Mn2+ is entering via voltage-dependent Ca2+ channels in the ileal cell membranes and it directly activates the contractile elements.
Nasu
T
T
Department of Veterinary Pharmacology, Faculty of Agriculture, Yamaguchi University, Japan.
Arakaki
H
H
Shibata
H
H
D000818:Animals; D002118:Calcium / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D006168:Guinea Pigs; D007082:Ileum / Q000187:drug effects*; D007211:Indoles / Q000494:pharmacology*; D008297:Male; D008345:Manganese / Q000494:pharmacology*; D009130:Muscle, Smooth / Q000187:drug effects; D009543:Nifedipine / Q000494:pharmacology*; D011188:Potassium / Q000494:pharmacology*; D012433:Ryanodine / Q000494:pharmacology*
D004791:Enzyme Inhibitors; D007211:Indoles; D012433:Ryanodine; D008345:Manganese; D009543:Nifedipine; D011188:Potassium; D002118:Calcium; C000543:cyclopiazonic acid