Manganese ions penetrate via L-type Ca2+ channels and induce contraction in high-K+ medium in ileal longitudinal muscle of guinea-pig.

1. Mn2+ (5 mM) completely inhibited the K+ (10-60 mM)-induced ileal tonic tension to the baseline, however, the tension and Mn2+ uptake increased progressively, depending on the K+ concentration of above 35 mM. 2. The L-type Ca2+ channel blocker, D-600 and nifedipine inhibited the tension development and Mn2+ uptake after addition of Mn2+ in the high-K+ (60 mM) medium, however, T-type Ca2+ channel blocker, Ni2+ and amiloride had no effect on it. 3. D-600 and nifedipine inhibited the tension development and Mn2+ uptake in the presence of 5 mM Mn2+ in the Ca(2+)-free, high-K+ (60 mM) medium. 4. The results suggest that Mn2+ penetrates via L-type Ca2+ channels in the ileal cell membrane in a state of prolonged depolarization and activates the contractile elements.