Bicarbonate-Dependent Action of Bay K 8644 in the Smooth Muscle of the Rat Vas Deferens

Effects of Bay K 8644. partial depolarization with high potassium, and nifedipine on the dose-response curves of the rat vas deferens to norepinephrine, methacholine and KCl were investigated in HEPES-buffered physiological salt solution (PSS) with or without 20 mM sodium bicarbonate. In the bicarbonate-containing PSS, Bay K 8644 at 10-6 M enhanced the maximal contractions in response to norepinephrine, methacholine and KCl by 31.4, 103.3 and 40.1%, respectively. In the bicarbonate-free PSS, where the maximal contractions induced by norepinephrine, methacholine and KCl were 77.5, 75.0 and 68.2% of those in the bicarbonate-containing PSS, respectively, Bay K 8644 did not enhance the maximal contractile response to any of the agonists, although the contractions induced by low concentrations of KCl were increased by Bay K 8644. Increasing the potassium concentration in the PSS from 6 to 20 mM enhanced the maximal contractions in response to norepinephrine and methacholine in the bicarbonate-containing PSS, whereas in the bicarbonate-free PSS, the treatment decreased the contractions. In the two PSSs, nifedipine similarly inhibited the contraction in response to either 10-6 M norepinephrine or 68 mM KCl. These results suggest that bicarbonate ion modulates the function of the voltage-dependent calcium channel in the smooth muscle of the rat vas deferens.