The effect of high K+ depolarization and verapamil on 45Ca2+ fluxes in the canine myocardium.

The effects of high K+ depolarization and verapamil on Ca2+ uptake and the total intracellular Ca2+ content of canine ventricular muscle strips (approximately 0.5 mm thick) were investigated. High K+ (96 mM) increased Ca2+ uptake above control and maintained this enhanced uptake throughout a 90 second measuring period. Verapamil (5 X 10(-6) M) significantly (p less than 0.05) inhibited this high K+ stimulated uptake. However, verapamil (5 X 10(-6) M) also had a direct effect on Ca2+ fluxes, causing a significant increase in both Ca2+ uptake (p less than 0.001) and total intracellular Ca2+ content (p less than 0.001) in the resting tissue. Therefore, verapamil's apparent inhibition of high K+ stimulated Ca2+ uptake may have resulted from some mechanism other than Ca2+ channel blockade.