Intervention of two voltage-dependent calcium-entry pathways in the contractile response to acetylcholine and KCl in rat uterus.

The contractile response of rat uterine smooth muscle was investigated. Verapamil and diltiazem concentration-dependently relax the sustained contractions induced by KCl (56 mmol/l) or acetylcholine (10(-4) mol/l). This inhibitory effect was not not freely reversed by washing the tissue and subsequently no contractile response was obtained in depolarized tissue, but a lower biphasic response (phasic and tonic) to acetylcholine was observed. Addition of cumulative concentrations of CaCl2 (1.2-19.2 mmol/l) induced a partial recovery of the contractile response to acetylcholine or KCl, but addition of MgCl2 (1.2-19.2 mmol/l did not. When the channel was reactivated by a third addition of KCl or acetylcholine after treatment with Ca2+, both spasmogens-induced phasic contractions recovered towards the initial configuration but the tonic component was not restored under any conditions. No recovery of mechanical response could be observed after Mg2+ treatment.