Inhibitory effects of procaine on the electrical and mechanical activities of the smooth muscle cells of the guinea pig urinary bladder.

Modification of the effects of K, Ca, acetylcholine and rapid cooling by procaine were examined in the smooth muscle of the guinea pig urinary bladder. Contraction enhancement by procaine was observed in 5.9 mM K - and 23.6 mM K-Krebs solution but was not confirmed in 59 mM K solution. Procaine enhanced contraction in relation to membrane activities. Relationships between membrane potential and K concentration showed that procaine reduced K conductance. This effect decreased as K concentration increased. K-induced contracture was inhibited by procaine at 37 degrees and 10 degrees C. Procaine inhibited Ca- and acetylcholine-induced contractions in isotonic K2SO4-Locke solution. Rapid cooling contracture, initiated by lowering the temperature of the solution from 36 +/- 1 degrees C to 12 +/- 2 degrees C within 30 sec, was inhibited by procaine. From these results, it is concluded that procaine has an inhibitory effect on Ca permeation through the cell membrane and on Ca release from sequestered sites, and it is confirmed that procaine enhancement of spontaneous contractions is related to the spike activity resulting from depolarization which is caused by reduction of K conductance (KURIHARA, 1975). The mechanism of the procaine effect is discussed in relation to excitation-contraction coupling in the guinea pig urinary bladder.