pH-dependent effects of bepridil on Ca2+-extrusion across rat heart sarcolemma.

The inhibition by bepridil of ATP-dependent Ca2+-uptake and Na+/Ca2+-exchange was studied in isolated rat cardiac sarcolemmal vesicles over a pH range of 6.3 to 7.8. It was found that the protonated and deprotonated species of bepridil induced the same inhibition and no activation of these two transport systems. However, the intrinsic activities of both systems appeared to be strongly dependent on the pH.