The effect of cations on the electrical properties of the smooth muscle cells of the guinea-pig vas deferens

1. A study has been made of the effects of Na(+) and Ca(2+) on the responses generated by intracellular current pulses in smooth muscle cells of the guinea-pig vas deferens and upon the propagated action potential.2. Reduction of the extracellular Na(+) activity (a(Na)) to less than 30 mM did not alter the characteristics of the spike-like response to intracellular current pulses (the active response) or of the propagated action potential.3. Reduction of the extracellular Ca(2+) activity (a(Ca)) to 0.1 mM decreased the resting input resistance of the cells but increased the input resistance during the crest of the active response. Reduction of Ca(2+) decreased the overshoot of the action potential by 22 mV per tenfold change in Ca(2+) and the resting potential by 25 mV per tenfold change.4. Reduction of the extracellular Ca(2+), keeping the product a(Ca)/a(2) (Na) constant, did not change the resting potential, but decreased the action potential overshoot by 20 mV per tenfold change.5. It is suggested that part of the current responsible for the rising phase of the action potential is carried by Ca(2+).