Effects of anipamil on myocardial sarcolemmal and mitochondrial calcium transport, comparison with verapamil and nifedipine

The calcium antagonists anipamil, verapamil and nifedipine inhibited, dose dependently, passive and ATP-driven ⁴⁵Ca²⁺-uptake in purified rabbit ventricular sarcolemmal vesicles exposed to a wide range of free calcium concentration (from 0 to 200 μM). The IC₅₀ values for passive binding were virtually identical for all calcium antagonists and the inhibition was relatively independent of the amount of free calcium employed. On the contrary, the order of potency for inhibition of the ATP-driven calcium uptake was: anipamil > verapamil > nifedipine. The inhibition of nifedipine, at free calcium concentrations lower than 80 μM, was preceded by a slight stimulation. The inhibitory effects of anipamil and verapamil, but not those of nifedipine, on the ATP-driven calcium uptake were more evident with increasing external calcium concentration. Verapamil and nifedipine failed to modify the initial rate of mitochondrial calcium transport either in the presence or in the absence of ADP; on the contrary, anipamil induced a dose-dependent inhibition of mitochondrial calcium transport. The inhibition occurred over the whole range of calcium concentrations tested, independent of the presence of ADP. The effects of anipamil, but not those of verapamil and nifedipine, on sarcolemmal and mitochondrial calcium transport were long lasting and survived membrane isolation.