Nitric Oxide Modulates Ca Channels in Dorsal Root Ganglion Neurons Innervating Rat Urinary Bladder

Yoshimura, Naoki, Satoshi Seki, and William C. de Groat. Nitric oxide modulates Ca channels in dorsal root ganglion neurons innervating rat urinary bladder. J Neurophysiol 86: 304–311, 2001. The effect of a nitric oxide (NO) donor on high-voltage-activated Ca channel currents (ICa) was examined using the whole cell patch-clamp technique in L6–S1 dorsal root ganglion (DRG) neurons innervating the urinary bladder. The neurons were labeled by axonal transport of a fluorescent dye, Fast Blue, injected into the bladder wall. Approximately 70% of bladder afferent neurons exhibited tetrodotoxin (TTX)-resistant action potentials (APs), and 93% of these neurons were sensitive to capsaicin, while the remaining neurons had TTXsensitive spikes and were insensitive to capsaicin. The peak current density of nimodipine-sensitive L-type Ca channels activated by depolarizing pulses (0 mV) from a holding potential of 260 mV was greater in bladder afferent neurons with TTX-resistant APs (39.2 pA/pF) than in bladder afferent neurons with TTX-sensitive APs (28.9 pA/pF), while the current density of v-conotoxin GVIA-sensitive N-type Ca channels was similar (43–45 pA/pF) in both types of neurons. In both types of neurons, the NO donor, S-nitroso-Nacetylpenicillamine (SNAP) (500 mM), reversibly reduced (23.4– 26.6%) the amplitude of ICa elicited by depolarizing pulses to 0 mV from a holding potential of 260 mV. SNAP-induced inhibition of ICa was reduced by 90% in the presence of v-conotoxin GVIA but was unaffected in the presence of nimodipine, indicating that NO-induced inhibition of ICa is mainly confined to N-type Ca 21 channels. Exposure of the neurons for 30 min to 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ, 10 mM), an inhibitor of NO-stimulated guanylyl cyclase, prevented the SNAP-induced reduction in ICa. Extracellular application of 8-bromo-cGMP (1 mM) mimicked the effects of NO donors by reducing the peak amplitude of ICa (28.6% of reduction). Action potential configuration and firing frequency during depolarizing current pulses were not altered by the application of SNAP (500 mM) in bladder afferent neurons with TTX-resistant and -sensitive APs. These results indicate that NO acting via a cGMP signaling pathway can modulate N-type Ca channels in DRG neurons innervating the urinary bladder.