Abstract
The effects of Nn, Zn and Mg ions on the contraction of smooth muscle of taenia coli from guinea-pig were studied. Both Mn and Zn ions suppress both spontaneous and electrically induced contractions. The suppressing effect of Mn ion appears promptly and is reversible, while the effect of Zn appears slowly and is irreversible. These results suggest that Mn ion acts on the excitation process in the memb-rane and Zn ion acts not only on excitation in the membrane, but also directly on the contractile system. Ca ion competes with Mn and Zn ions in the suppression of both spontaneous and electrically induced contractions. However, the competition of Ca ion with Zn ion is effective only when Ca is present prior to the addition of Zn ion.
