Electrophysiological and neurochemical evidence for voltage-dependent Ca(2+) channel blockade by a novel...

The effects of a neuroprotective agent 4-(4-fluorophenyl)-2-methyl-6-(5-piperidinopentyloxy) pyrimidine hydrochloride (NS-7) on the Ca(2+) currents in rat dorsal root ganglion neurones and on the depolarization-evoked nitric oxide synthesis, which was estimated from cyclic GMP formation in slices of the rat cerebral cortex, were investigated, and its mode of action was compared with those of typical Ca(2+) channel blockers. In rat dorsal root ganglion neurones, NS-7 (0.3-100 microM) inhibited the whole-cell Ba(2+) currents (IBa) in a voltage-dependent manner, in which the compound more potently blocked the IBa elicited from the holding potential of -40 mV than that induced from -80 mV. In slices of rat cerebral cortex, KCl-evoked nitric oxide synthesis was markedly inhibited by omega-conotoxin GVIA and omega-agatoxin IVA, but only slightly attenuated by nifedipine, suggesting that the response is mediated predominantly through activation of N-type and P/Q-type Ca(2+) channels. NS-7 (1-100 microM) inhibited the KCl-stimulated nitric oxide synthesis in a manner dependent on the intensity of the depolarizing stimuli. Moreover, weak but significant inhibitory effect of NS-7 was observed even after wash-out. Similar voltage-dependent inhibition of the KCl response was observed by a limited concentration (10 microM) of verapamil. These findings indicate that NS-7 in several concentrations blocks Ca(2+) channel in a voltage-dependent manner.