RELATIONSHIP BETWEEN EFFECTS OF PROCAINE AND Ca ON SPONTANEOUS ELECTRICAL AND MECHANICAL ACTIVITIES OF THE SMOOTH MUSCLE CELLS OF THE GUINEA PIG URINARY BLADDER

Abstract

The relationships between the effects of procaine and those of Ca on the spontaneous electrical and mechanical activities of smooth muscle cells of the guinea pig urinary bladder were studied using both microelectrode and sucrose gap methods. Procaine (1, 7, and 15 mM) depolarized the membrane and increased spontaneous spike frequency. The maximum rates of rise and fall and the after-hyperpolarization of the spike decreased. Enhanced spontaneous rhythmic contractions accompanied these membrane activities (1 mM). The tone of the preparation (resting tension) increased transiently and decreased gradually (7-15 mM). These procaine effects were suppressed by the application of excess Ca (7.5 mM). The increased electrotonic potential induced by 7 mM procaine was reduced by the addition of 7.5 mM Ca. Reduction of Ca concentration (0.8 and 0 mM) in Krebs solution containing procaine further depolarized the membrane and decreased the spike amplitude. In Ca-deficient solution, the enhanced rhythmic contractions induced by procaine were slightly reduced. Compound D600 (1-3mg/1), manganese ion (Mn)(1-3 mM), and cobalt ion (Co)(1-3 mM) inhibited the effects of procaine on spike discharges and mechanical responses. From these results it is concluded that procaine action is related to that of Ca which controls the membrane permeability, since procaine depolarizes the membrane by reducing K conductance. Furthermore, action potentials observed in the Krebs solution containing procaine are considered to be Ca spikes, which seem to play an important role in excitation-contraction coupling in the guinea pig urinary bladder smooth muscle.