Abstract
Procaine (1-15mM) 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 substitution) Krebs solutions. Tetrodotoxin (3×10-7g/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 1mM of procaine, but was suppressed at concentrations of more than 5mM. After-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 1mM 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. From these results it is suggested that procaine mainly reduces K conductance and causes depolarization, and that enhanced spontaneous contractions are caused by depolarization and increased spike activity.
