THE EFFECT OF PROCAINE ON THE MECHANICAL AND ELECTRICAL ACTIVITIES OF THE SMOOTH MUSCLE CELLS OF THE GUINEA PIG URINARY BLADDER

Abstract

Procaine (1-15 mM) enhanced the spontaneous contractions of the urinary bladder smooth muscle. When a low concentration of procaine was added to normal Krebs solution, spontaneous rhythmic contractions were enhanced. On increasing the concentration of procaine, a rise in tone (resting tension) of the preparation was observed and gradually decreased with time. The action of procaine of enhancing spontaneous contraction was observed in Na-deficient (sucrose substitution) and Na-free (Tris [tris(hydroxymethyl)aminomethane] substitution) Krebs solutions. Tetrodotoxin (3 .times. 10-7 g/ml) did not inhibit the effect of procaine on mechanical response. In normal Krebs solution, procaine depolarized the membrane and increased spike frequency. The peak potential of the spike increased at 1 mM of procaine, but was suppressed at concentrations of more than 5 mM. Hyperpolarization of the spike was diminished by procaine and spike duration was prolonged. The maximum rate of rise of the spike was increased immediately after application of 1 mM of procaine, but decreased with time. The maximum rate of fall of the spike was markedly decreased by procaine. Relative membrane resistance was increased by the application of procaine. Procaine mainly reduces K conductance and causes depolarization. Enhanced spontaneous contractions are caused by depolarization and increased spike activity.