Effects of magnesium ions on the contraction of the rat detrusor muscle

: Effects of magnesium (Mg) ions on the contraction of the rat detrusor muscle induced by intramural nerve stimulation were investigated in vitro. 1. Frequency-response curve demonstrated that contractile responses increased in magnesium-free Krebs' solution and decreased in high magnesium solution (MgCl2 5 mM) in comparison with those in normal Krebs' solution. 2. When MgCl2 was added into an organ bath with cumulative way, the magnitude of detrusor contraction decreased dose-dependently. The contractile response was completely abolished by 30 mM MgCl2. 3. Mg ions suppressed the detrusor contraction induced by a high KCl concentration. 4. The effect of Mg ions on the detrusor contraction was enhanced by verapamil but was inhibited by Bay-K8644. 5. Procaine agonized the effect of Mg ions on the detrusor contraction. On the other hand, caffeine did not modify the effect of Mg ions. These results suggest that Mg ions seem to play an inhibitory role on 2 types of Ca-channels existing on the cell membrane and to inhibit release of Ca ions from the intracellular deposit.