Effects of m-nisoldipine on contraction and 45Ca influx in isolated rat aorta

m-Nisoldipine caused a concentration-dependent depression of the contractile response and 45Ca influx evoked by KCl in isolated rat thoracic aorta. The IC50 value for contraction and 45Ca influx were 0.69 (95% confidence limits 0.32-1.5) nmol.L-1 and 0.35 (95% confidence limits 0.06-2.0) nmol.L-1, respectively. There was a positive correlation between the inhibition of KCl-evoked contraction and 45Ca influx (r = 0.996). m-Nisoldipine (0.1-10 mumol.L-1) did not influence the 45Ca influx into resting cells and failed to inhibit noradrenaline (1.0 mumol.L-1)-evoked contraction and 45Ca influx. The results suggest that the relaxant effect of m-nisoldipine on rat aorta may be closely related to the blockade of Ca2+ entry through a potential-dependent calcium channel.