Possible mechanism of dantrolene stabilization of cultured neuroblastoma cell plasma membranes.

Some reports have suggested that dantrolene interacts directly with the membrane bilayer. We investigated effects of dantrolene on changes in membrane properties induced by compound 48/80 (C48/80), a membrane stimulator. The addition of C48/80 for 1 min elicited a rapid, dose-dependent Ca2+ influx, which was reduced to 14% by the absence of external Ca2+. Dantrolene inhibited the C48/80-induced increase in Ca2+ permeability of plasma membranes in a concentration-dependent manner (0.33-10 microM, IC50 value was 5 microM). We next examined C48/80-induced changes in structural and dynamic membrane properties by electron spin resonance (ESR). The ratio h0/h-1 was determined to evaluate membrane fluidity. C48/80 increased the membrane fluidity in a concentration-dependent manner (0.1-0.56 mg/ml). Dantrolene (10 microM) itself did not change the membrane fluidity, but it significantly reduced the C48/80-induced increase in membrane fluidity (0.56 mg/ml). Moreover, the C48/80-induced increase in fluidity was dependent on extracellular Ca2+. We conclude that dantrolene protects neuroblastoma cell plasma membrane from C48/80-induced membrane perturbation, which causes Ca2+ influx and an increase in membrane fluidity. These findings strongly suggest that dantrolene directly stabilizes the neuronal plasma membrane.