RESUMEN
There is growing evidence for a nitric oxide/cyclic GMP pathway of signal transduction in the vestibular system. Recently, two isoforms of nitric oxide (NO) synthase (nNOS and eNOS) and NO itself have been identified at the light microscopic level in the vestibulocochlear system of mice using specific antibodies and a new fluorescence indicator. In order to acquire more information about signal transduction and tissue modulation in this neuroepithelium at the cellular and subcellular levels, ultrathin sections of London Resin White-embedded saccule maculae of the frog Rana pipiens were incubated with various concentrations of commercially available antibodies to nNOS and eNOS. The immunoreactivity was visualized by a gold-labelled secondary antibody and the amount of the immunoreactions per microm2 was quantified for the different cell types and subcellular regions. Significant eNOS immunoreactivity was identified in the hair bundles, cuticular plates and the rest of the cytoplasm of the hair cells as well as in different subcellular regions of the supporting cells. Gold-labelled anti-nNOS antibodies stained mainly stereovilli and cuticular structures of hair cells and supporting cells, whereas the number of the immunoreactions in the remaining cytoplasm of both cell types was near the background level. The spatial co-localization of the two NOS isotypes in the same cell regions of hair cells and supporting cells was confirmed in double-labelling experiments. The immunocytochemical findings are suggestive of a redundant system in which one NOS isoform can (partially) replace the other. The different subcellular localization of the NOS isoforms may allow for isoform specific regulation of NOS activity by different Ca2+ currents at the subcellular level, underlining the importance of NO-regulated processes in neuroepithelia of the inner ear.
Asunto(s)
Máculas Acústicas/enzimología , Óxido Nítrico Sintasa/análisis , Rana pipiens , Máculas Acústicas/ultraestructura , Animales , Células Ciliadas Auditivas/enzimología , Células Ciliadas Auditivas/ultraestructura , Inmunohistoquímica , Isoenzimas/análisis , Microscopía Inmunoelectrónica , Óxido Nítrico Sintasa/biosíntesis , Óxido Nítrico Sintasa/inmunología , Óxido Nítrico Sintasa de Tipo I , Óxido Nítrico Sintasa de Tipo III , Órgano Espiral/enzimología , Órgano Espiral/ultraestructura , Rana pipiens/anatomía & histología , Rana pipiens/fisiologíaRESUMEN
Larval cichlid fish (Oreochromis mossambicus) were kept at hypergravity (hg; centrifuge) for 6 h. Following the transfer to 1 g (i.e. stopping the centrifuge), animals were separated into normally and abnormally (kinetotic) swimming individuals (the latter were swimming kinetotically, i.e. performing spinning movements). Subsequently, carbonic anhydrase- (CA-) reactivity was histochemically demonstrated and densitometrically determined in inner ear maculae. It was found that both the total macular CA-reactivity as well as the difference in reactivates between left and right maculae were significantly lower in normally swimming hg-animals as compared to the kinetotically behaving hg-fish (P<0.0001). This result is in complete agreement with closely related studies carried out on the calcium incorporation of inner ear otoliths and indicates that a regulatory mechanism, which adjusts otolithic calcium carbonate incorporation towards the gravity vector, acts via activation/deactivation of macular CA.
Asunto(s)
Anhidrasas Carbónicas/metabolismo , Oído Interno/enzimología , Actividad Motora , Natación , Máculas Acústicas/enzimología , Animales , Centrifugación , Hipergravedad , TilapiaRESUMEN
This study was undertaken to assess the localization of the Na+,K+-ATPase in the neuroepithelial cells of the macula sacculi. In vitro perilymphatic (basolateral) perfusion with ouabain produced a significant drop in the membrane potential. Endolymphatic (apical) application of ouabain had practically no effect on membrane potentials. This suggests that Na+,K+-ATPase is asymmetrically distributed in the neuroepithelial cells.