Neuronal Ca²⁺ Channel Blocking Action of an Antihypertensive Drug, Cilnidipine, in IMR-32 Human Neuroblastoma Cells

Abstract

Although the anti-sympathetic mechanisms of the antihypertensive drug cilnidipine have been analyzed in neuronal cells derived from rodents, there is little information regarding the effects of cilnidipine in human neuronal cells. We investigated the effects of cilnidipine on N-type Ca²⁺ channels in IMR-32 human neuroblastoma cells using fura-2-based microfluorimetry. The ratio of the intensities of the emitted fluorescence at an excitation wavelength of 340 nm to that at 380 nm was calibrated to estimate the intracellular concentration of Ca²⁺. Stimulation of IMR-32 cells by 40 mmol/l KCl immediately increased the intensities ratio. In the presence of 10 μmol/l of nifedipine to block L-type Ca²⁺ channels, ω-conotoxin GVIA, a selective N-type Ca²⁺ channel blocker, in a concentration of 1 μmol/l suppressed the elevation of the intensities ratio induced by 40 mmol/l KCl. Similarly, cilnidipine in a concentration of 10 μmol/l suppressed the elevation of the ratio induced by 40 mmol/l KCl, and this suppression was effectively inhibited after the treatment with ω-conotoxin GVIA. These results suggest that cilnidipine potentially inhibits N-type Ca²⁺ channels in human neuronal cells and might be applied as a prospective therapeutic tool to provide neuronal protection as well as its antihypertensive effects and anti-sympathetic actions. (Hypertens Res 2003; 26: 743-747)