Inhibitory Effect of Nitric Oxide on Voltage-Dependent Calcium Currents in Rat Dorsal Root Ganglion Cells

Abstract

The effect of nitric oxide (NO) on calcium current (ICa) and intracellular calcium concentration ([Ca2+]i) in primarily cultured dorsal root ganglion (DRG) neurons was investigated from neonatal rats. ICa and [Ca2+]i were simultaneously recorded using perforated-patch technique in combination with fluorescence measurement from single DRG neurons. NO donors, sodium nitroprusside (SNP) and S-nitro-N-acetylpenicillamine (SNAP), inhibited ICa in small-diameter neurons without significant change in voltage-dependence of activation and activation time constants. SNP and SNAP also reduced the transient [Ca2+]i peak accompanied by ICa. Inhibition by NO was reproducible, but gradually desensitized. In some DRG neurons, SNP and SNAP increased basal [Ca2+]i in concentration of 10 μM with little effect on NO-induced inhibition of ICa. 8-Br-cGMP, a permeable cGMP analog, mimicked the effects of SNP and SNAP. These results suggest that, in DRG neurons, NO has inhibitory effect on ICa, which is independent of NO-induced increase of basal [Ca2+]i, through cGMP-dependent pathway.