At concentrations of 0.5-2.0 mM, Bunaftide causes contraction and rounding of the cells with loss of microvilli-like processes. Aggregates of dense, partly granular, partly fibrillar material form in the cytoplasm and the rough endoplasmic reticulum became vesiculated. Bundles of actin filaments are disrupted, forming rings, coils, and granules. 0.4 mM Bunaftide increases and 0.8-1.0 mM markedly decreases the percentage of mitotic cells, without accumulation of cells in any particular stage of mitosis. The drug may arrest the cell cycle at some point before mitosis; it may have a critical concentration above which the arrest becomes permanent. Bunaftide at 1, 5 and 10 mg/L produces a concentration-dependent depression of the maximum rate of rise of the action potential in guinea pig papillary muscle preparations without affecting the resting membrane potential and the action potential amplitude. The action potential duration (APD50, APD90) is significantly prolonged by the treatment with 1 and 5 mg/L Bunaftide, while it is not changed by the treatment with 10 mg/L.
