Actions and interactions of dihydropyridines and ethanol on the rat sinus node

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Abstract
Summary The actions and interactions of dihydropyridines (DHPs) and ethanol on sinus node (SN) automaticity were studied using rat sinoatrial preparations superfused with Tyrode's solution at 37°C. Intracellular microelectrodes were used to monitor SN rate (SNR). The automaticity of the SN was not affected by nimodipine 10−10 M, but it was depressed by a higher concentration of this calcium antagonist (10−8 M). The racemic compound (±)Bay K 8644 had a dosedependent biphasic chronotropic action: At 10−8 M it decreased the SNR, while at 10−7 M it increased the SNR. The negative component was blocked by atropine. A small concentration of ethanol (1.8×10−2 M) had a positive chronotropic effect on the SN, and this action was blocked by nimodipine 10−10 M. This small concentration of ethanol did not modify the chronotropic effects of either of the DHPs. A higher concentration of ethanol (5.3×10−2 M) did not by itself affect the SNR, but it antagonized the chronotropic actions of the two DHPs.