Responses of cultured heart cells to procainamide and lignocaine

Summary: The effects of procainamide and lignocaine, in concentractions from 10^-6 to 10^-2mol·litre^-1, on the Na influx and contraction frequency of cultured heart cells were studied. Both drugs produced a prompt, dose-dependent reduction in Na influx which was significant (P<0.0l) for all concentrations tested. Lignocaine affected only that portion of the Na influx which was also verapamil-sensitive, whereas procainamide suppressed in addition, the verapamil-insensitive influx. In addition both drugs produced a concomitant decrease in the spontaneous contraction frequency of the cells. A close linear correlation (r - 0.99) between verapamil-sensitive Na influx and contraction frequency, in the presence of both procainamide and lignocaine was found. From this, and previous studies indicating a dependency of contraction frequency on the inward verapamil-sensitive Na influx, it is suggested that the drugs modify the automaticity of this preparation by a primary influence on membrane Na exchange.