Inhibitory action of calcium antagonists on atp-dependent calcium uptake by the renal cortical microsomes

Effects of Ca²⁺ antagonists, verapamil and diltiazem, on uptake and release of Ca²⁺ by microsomes of the renal cortex were studied. Verapamil inhibited the ATP-dependent Ca²⁺ uptake by renal microsomes. Addition of 0.8 mM verapamil was required to produce 50% inhibition of the ATP-dependent Ca²⁺ uptake. Diltiazem also depressed the Ca²⁺ uptake of the microsomes. The inhibitory effect of both drugs on the Ca²⁺ uptake was not due to an increased permeability for Ca²⁺, since release of Ca²⁺ from the microsomes was not significantly affected by either drug. It is proposed that verapamil and diltiazem inhibit Ca²⁺ transport by interfering with an active process of Ca²⁺ accumulation in microsomes of the renal cortex.