The Effect of a Calcium‐antagonistic Drug, Nifedipine, on the Mechanical and Electrical Activity of the Isolated Rat Atrium

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Abstract
Effects of a calcium‐antagonistic drug, nifedipine, on the mechanical and electrical behaviour of isolated rat atria were investigated in the concentration range from 0.5 to 1000 μg/l. Nifedipine caused a dose‐dependent decrease in the spontaneous atrial rate and amplitude of contractions, and atrial arrest occurred in some experiments with the highest drug concentrations. The drug also caused a dose‐dependent decrease in contractile force of stimulated left atria, while the threshold current required to drive the atria was unchanged. The effective refractory period was unaltered in the concentration range between 0.5 and 500 μg/l since the maximum following frequency at which the atria could respond to stimulation was unchanged. Nifedipine caused a dose‐dependent increase in the sinus node recovery time. The present study indicates that calcium ions are necessary for pacemaker activity in the sino‐atrial node, but not essential for maintaining atrial refractoriness and excitability.

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