Nitric oxide decreases capsaicin-activated currents in dorsal root ganglion neuron via cGMP/protein kinase G-dependent pathway and S-nitrosylation

초록

Nitric oxide (NO) modulates a variety of physiological functions, such as vasodilation, platelet aggregation, apoptosis and neurotransmission. The actions of NO primarily involve the activation of soluble guanylyl cyclase (sGC) that stimulates the production of cGMP as well as S-nitrosylation of proteins. In the present study, we investigated the effect of NO on capsaicin-activated inward currents (Icap) in dorsal root ganglion (DRG) neurons and the intracellular mechanism involved using the whole-cell patch clamp recording. The NO donor, sodium nitroprusside (SNP) reversibly decreased the amplitude of Icap in a dose-dependent manner. NO significant inhibition was abolished when SNP was applied together with the NO scavenger, hemoglobin (20 μM). 8-bromo-cGMP (100 μM), a membrane permeable analog of cGMP, mimicked the effect of SNP. 8-pCPT-cGMP (100 μM), a more potent cGMP analog than 8-Br-cGMP, also mimicked the effect of SNP. The effects of SNP on Icap were partially blocked by specific inhibitors of guanylyl cyclase, 1H-[1,2,4]oxidiazolo[4,3-a]quinoxalin-1-one (ODQ, 10 μM). Furthermore, non-specific inhibitor of phosphodiesterases, 3-isobutyl-1-methylxanthine (IBMX, 1 mM) augmented blocking effect of SNP. Pretreatment with the PKG inhibitor, KT 5823 (1 mM) potentially abolished the effect of SNP on Icap. On the other hand, a sulfhydryl alkylating agent, N-ethylmaleimide (NEM, 1 mM) partially blocked the effect of SNP on Icap. Similarly, the sufhydryl reducing agent dithiothreitol (DTT, 10 mM) and glutathione (GSH, 4 mM) also partially blocked the No-induced Icap decrease. These results suggest that cGMP/PKG-dependent pathway and S-nitrosylation may be involved in the NO-induced inhibition of Icap in rat DRG neurons.