Electrophysiological Effects of Procaine in Rabbit Sino-Atrial Node Cells

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Abstract
Effects of procaine (50-500 .mu.g/ml) on membrane potential and currents were investigated using a two microelectrode-voltage clamp technique. Procaine reduced the action potential amplitude (APA), the maximum diastolic potential and the maximum rate of depolarization (.ovrhdot.Vmax) in a dose-dependent manner. At the same time, the action potential duration and the cycle length were prolonged. In voltage clamp experiments, procaine (50 .mu.g/ml) did not affect the slow inward current (lsi), but reduced the time-dependent outward current (lk). At concentrations higher than 100 .mu.g/ml, procaine reduced both currents and the inward current activated by hyperpolarization in a dose-dependent manner. In 7 of 20 specimens, a low concentration of procaine (50 or 100 .mu./ml) increased Isi which enhanced the .ovrhdot.VMax and APA, but did not increase lk. Procaine did not affect the steady-state inactivation of lsi (f.infin.) and the activation of lk (p.infin.). The results suggest that the depressions of currents induced by procaine are due to a reduction in conductances of the current systems.

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