INTERVENTION OF 2 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 sustaine d contractions induced by KCl (56 mmol/l) or acetylcholine (10(-4) mol /l). This inhibitory effect was not freely reversed by washing the tis sue and subsequently no contractile response was obtained in depolariz ed tissue, but a lower biphasic response (phasic and tonic) to acetylc holine 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 ac etylcholine 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 mecha nical response could be observed after Mg2+ treatment.