Membrane electrical properties of guinea pig bladder smooth muscle with growth

The effect of growth on bladder membrane electrical properties was studied in guinea pigs. The electrical activity of the smooth muscle membrane in dertusor muscle strips from immature (6–8 wk) and mature (22–24 wk) guinea pigs was investigated using an intracellular microelectrode technique. The parameters measured included resting membrane potential, membrane time constant, and the action potential (AP) kinetics. The results of this study can be summarized as follows: 1) Bladder weight increased with animal growth. 2) Growth did not affect the detrusor smooth muscle resting membrane potential or membrane time constant. 3) The configuration of the detrusor muscle AP (amplitude, after hyperpolarization, and overshoot potential) and indices of AP kinetics (maximum velocities of depolarization and repolarization) were similar in immature and mature animals. The AP duration, however, showed slight prolongation in the mature adult group. These results indicate that, in the guinea pig, the passive and active electrical properties of the detrusor smooth muscle membrane do not change significantly with growth.