Involvement of the nitric oxide-cyclic GMP pathway and neuronal nitric oxide synthase in ATP-induced Ca2+ signalling in cochlear inner hair cells.
We recently demonstrated that extracellular adenosine 5'-triphosphate (ATP) induced nitric oxide (NO) production in the inner hair cells (IHCs) of the guinea pig cochlea, which inhibited the ATP-induced increase in the intracellular Ca(2+) concentrations ([Ca(2+)](i)) by a feedback mechanism [Shen, J., Harada, N. & Yamashita, T. (2003) Neurosci. Lett., 337, 135-138]. We herein investigated the role of the NO-cGMP pathway and neuronal NO synthase (nNOS) in the ATP-induced Ca(2+) signalling in IHCs using the Ca(2+)-sensitive dye fura-2 and the NO-sensitive dye DAF-2. Fura-2 fluorescence-quenching experiments with Mn(2+) showed that ATP triggered a Mn(2+) influx. L-N(G)-nitroarginine methyl ester (L-NAME), a nonspecific NOS inhibitor, accelerated the ATP-induced Mn(2+) influx while S-nitroso-N-acetylpenicillamine (SNAP), a NO donor, suppressed it. 1H-[1,2,4]oxadiazole[4,3-a] quinoxalin-1-one, an inhibitor of guanylate cyclase, and KT5823, an inhibitor of cGMP-dependent protein kinase, enhanced the ATP-induced [Ca(2+)](i) increase. 8-Bromoguanosine-cGMP, a membrane-permeant analogue of cGMP mimicked the effects of SNAP. Moreover, the effects of 7-nitroindazole, a selective nNOS inhibitor, mimicked the effects of L-NAME regarding both the enhancement of the ATP-induced Ca(2+) response and the attenuation of NO production. Immunofluorescent staining of nNOS using a single IHC revealed that nNOS was distributed throughout the IHCs, but enriched in the apical region of the IHCs as shown by intense staining. In conclusion, the ATP-induced Ca(2+) influx may be the principal source for nNOS activity, which may interact with P2X receptors in the apical region of IHCs. Thereafter, NO can be produced and conversely inhibits the Ca(2+) influx via the NO-cGMP-PKG pathway by a feedback mechanism.
Hearing Research Laboratory, Department of Otolaryngology, Kansai Medical University, Fumizonocho 10-15, Moriguchi, Osaka 570-8507, Japan.
Jing
J
Shen
Narinobu
N
Harada
Hiroko
H
Nakazawa
Toshio
T
Yamashita
D000255:Adenosine Triphosphate / Q000378:metabolism* / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology*; D006152:Cyclic GMP / Q000031:analogs & derivatives / Q000378:metabolism*; D017869:Cyclic GMP-Dependent Protein Kinases / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D025461:Feedback, Physiological / Q000502:physiology; D005452:Fluoresceins; D016257:Fura-2; D006168:Guinea Pigs; D006199:Hair Cells, Auditory, Inner / Q000187:drug effects / Q000378:metabolism*; D007150:Immunohistochemistry; D008345:Manganese / Q000378:metabolism; D009419:Nerve Tissue Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D009569:Nitric Oxide / Q000378:metabolism*; D020030:Nitric Oxide Donors / Q000494:pharmacology; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D052248:Nitric Oxide Synthase Type I; D018048:Receptors, Purinergic P2 / Q000187:drug effects / Q000378:metabolism; D058469:Receptors, Purinergic P2X; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology
C112456:4,5-diamino-2-(3,6-dihydroxy-9H-xanthen-9-yl)benzoic acid; D004791:Enzyme Inhibitors; D005452:Fluoresceins; D009419:Nerve Tissue Proteins; D020030:Nitric Oxide Donors; D018048:Receptors, Purinergic P2; D058469:Receptors, Purinergic P2X; D009569:Nitric Oxide; D008345:Manganese; D000255:Adenosine Triphosphate; D019001:Nitric Oxide Synthase; D052248:Nitric Oxide Synthase Type I; D017869:Cyclic GMP-Dependent Protein Kinases; D006152:Cyclic GMP; D002118:Calcium; D016257:Fura-2