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The present study examined the ventricular arrhythmic and electrophysiological properties during hyperkalemia (6.3 mM [K + ] vs. 4 mM in normokalemia) and anti-arrhythmic effects of hypercalcemia (2.2 mM [Ca 2+ ]) in Langendorff-perfused mouse hearts. Monophasic action potential recordings were obtained from the left ventricle during right ventricular pacing. Hyperkalemia increased the proportion of hearts showing provoked ventricular tachycardia (VT) from 0 to 6 of 7 hearts during programmed electrical stimulation (Fisher's exact test, P&lt;0.05). It shortened the epicardial action potential durations (APD x ) at 90, 70, 50 and 30% repolarization and ventricular effective refractory periods (VERPs) (analysis of variance, P&lt;0.05) without altering activation latencies. Endocardial APD x and VERPs were unaltered. Consequently, ∆APD x (endocardial APD x -epicardial APD x ) was increased, VERP/latency ratio was decreased and critical intervals for reexcitation (APD 90 -VERP) were unchanged. Hypercalcemia treatment exerted anti-arrhythmic effects during hyperkalemia, reducing the proportion of hearts showing VT to 1 of 7 hearts. It increased epicardial VERPs without further altering the remaining parameters, returning VERP/latency ratio to normokalemic values and also decreased the critical intervals. In conclusion, hyperkalemia exerted pro-arrhythmic effects by shortening APDs and VERPs. Hypercalcemia exerted anti-arrhythmic effects by reversing VERP changes, which scaled the VERP/latency ratio and critical intervals.

Anti-arrhythmic effects of hypercalcemia in hyperkalemic, Langendorff-perfused mouse hearts