FLUSPIRILENE BLOCK OF N-TYPE CALCIUM CURRENT IN NGF-DIFFERENTIATED PC12 CELLS

1 High voltage-activated calcium currents were recorded in nerve growth factor (NGF)-differentiated PC12 cells with the whole-cell patch clamp technique. After exposure to NGF for 3-10 days the PC12 cells developed neurone-like processes and calcium currents which were pharmacologically separable into L- and N-types (defined by sensitivity to nifedipine and omega-conotoxin GVIA respectively). 2 After blocking the L-type calcium channels with nifedipine (1O mu M), omega-conotoxin GVIA blocked approximately 85% of the remaining calcium current with an IC50 of 3nM and a Hill coefficient of 1. The block by conotoxin GVIA was irreversible on the time scale of these experiments. These results suggested that the majority of the nifedipine-insensitive calcium current was N-type. 3 Fluspirilene, a substituted diphenylbutylpiperidine with potent neuroleptic properties, reversibly inhibited the N-type component in a dose-dependent manner with an IC50 of 30nM. The Hill coefficient of the block was 0.25. The fraction of current blocked was the same at all test potentials examined (-30 to +40mV). 4 These data indicate that the neuroleptic properties of fluspirilene may be due, at least in part, to an inhibition of neuronal N-type calcium channels. This finding raises the possibility that modulation of N-type calcium channel activity by drugs derived from substituted diphenylbutylpiperidines may provide a novel way of altering neurotransmitter release and hence brain function.