Uptake of bepridil into isolated ventricular myocytes. Retention by actin

Isolated rat ventricular myocytes accumulate large amounts of bepridil intracellularly. The mode of transport is uncertain but uptake is of such a magnitude as to mask possible sarcolemmal binding sites. Bepridil is tightly bound within myocytes, there being only a minimal efflux into bepridil-free medium. Purified F-actin binds bepridil in excess of 2 moles/mole actin, sufficient to account for the uptake of bepridil by myocytes incubated in 10 microM drug. At higher bepridil concentrations the amount transported into myocytes suggests that the drug may be distributed between actin-bound and cytoplasmic pools. Bepridil may alter cardiac contractility by a direct influence on the contractile filaments.