EFFECTS OF NIFEDIPINE ON CONTRACTION BY MN2-FREE, HIGH-K+ MEDIUM IN ILEAL LONGITUDINAL MUSCLE( IN CA2+)

1. The tension development due to 5 mM Mn2+ in Ca2+-free medium was de pendent on the external K+ concentration above 35 mM in ileal muscle. 2. Nifedipine, an L-type Ca2+ channel blocker, dose dependently inhibi ted both the contraction and the manganese uptake by the application o f 5 mM Mn2+ in the Ca2+-free, 35-60 mM K+ medium. 3. These results sug gest that Mn2+ is entering through voltage dependent Ca2+ channels dep ending on ileal membrane depolarization, and it directly activates the contractile protein. (C) 1998 Elsevier Science Inc.