Nitric oxide modulates Ca(2+) channels in dorsal root ganglion neurons innervating rat urinary bladder.
The effect of a nitric oxide (NO) donor on high-voltage-activated Ca(2+) channel currents (I(Ca)) was examined using the whole cell patch-clamp technique in L(6)-S(1) 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 TTX-sensitive spikes and were insensitive to capsaicin. The peak current density of nimodipine-sensitive L-type Ca(2+) channels activated by depolarizing pulses (0 mV) from a holding potential of -60 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 omega-conotoxin GVIA-sensitive N-type Ca(2+) channels was similar (43-45 pA/pF) in both types of neurons. In both types of neurons, the NO donor, S-nitroso-N-acetylpenicillamine (SNAP) (500 microM), reversibly reduced (23.4-26.6%) the amplitude of I(Ca) elicited by depolarizing pulses to 0 mV from a holding potential of -60 mV. SNAP-induced inhibition of I(Ca) was reduced by 90% in the presence of omega-conotoxin GVIA but was unaffected in the presence of nimodipine, indicating that NO-induced inhibition of I(Ca) is mainly confined to N-type Ca(2+) channels. Exposure of the neurons for 30 min to 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ, 10 microM), an inhibitor of NO-stimulated guanylyl cyclase, prevented the SNAP-induced reduction in I(Ca). Extracellular application of 8-bromo-cGMP (1 mM) mimicked the effects of NO donors by reducing the peak amplitude of I(Ca) (28.6% of reduction). Action potential configuration and firing frequency during depolarizing current pulses were not altered by the application of SNAP (500 microM) 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(2+) channels in DRG neurons innervating the urinary bladder.
Yoshimura
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Department of Pharmacology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261, USA. nyos@pitt.edu
Seki
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de Groat
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D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D000818:Animals; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020746:Calcium Channels, L-Type / Q000502:physiology; D020864:Calcium Channels, N-Type / Q000502:physiology*; D002211:Capsaicin / Q000494:pharmacology; D006152:Cyclic GMP / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D005727:Ganglia, Spinal / Q000166:cytology*; D009412:Nerve Fibers / Q000187:drug effects / Q000378:metabolism; D009413:Nerve Fibers, Myelinated / Q000187:drug effects / Q000378:metabolism; D009475:Neurons, Afferent / Q000378:metabolism* / Q000648:ultrastructure; D009553:Nimodipine / Q000494:pharmacology; D009569:Nitric Oxide / Q000378:metabolism*; D020030:Nitric Oxide Donors / Q000494:pharmacology; D010069:Oxadiazoles / Q000494:pharmacology; D010396:Penicillamine / Q000031:analogs & derivatives / Q000494:pharmacology; D011810:Quinoxalines / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D013779:Tetrodotoxin / Q000494:pharmacology; D001743:Urinary Bladder / Q000294:innervation*; D020866:omega-Conotoxin GVIA / Q000494:pharmacology
C095284:1H-(1,2,4)oxadiazolo(4,3-a)quinoxalin-1-one; D002121:Calcium Channel Blockers; D020746:Calcium Channels, L-Type; D020864:Calcium Channels, N-Type; D004791:Enzyme Inhibitors; D020030:Nitric Oxide Donors; D010069:Oxadiazoles; D011810:Quinoxalines; C110881:S-nitro-N-acetylpenicillamine; D015124:8-Bromo Cyclic Adenosine Monophosphate; D009569:Nitric Oxide; D013779:Tetrodotoxin; D009553:Nimodipine; D020866:omega-Conotoxin GVIA; D010396:Penicillamine; D006152:Cyclic GMP; D002211:Capsaicin