RESUMO
Little is known about the cells or mechanisms of O2 chemoreception in vertebrates other than mammals. The purpose of this study, therefore, was to identify O2-sensitive chemoreceptors in a fish. Putative O2-sensitive chemoreceptors were dissociated from the gills of channel catfish, Ictalurus punctatus, and cultured. A population of cells was identified with morphology and a histochemical profile similar to mammalian carotid body Type I (glomus) cells and pulmonary neuroepithelial cells. These cells stain with neutral red and appear to be the branchial neuroepithelial cells. Immunocytochemical staining showed that these cells contain neuron-specific enolase (NSE), tyrosine hydroxylase (TH) and 5-hydroxytryptamine (5HT). Patch-clamp experiments showed that these cells have a O2-sensitive, voltage-dependent outward K+ current like mammalian O2 sensors. Two kinds of electrophysiological responses to hypoxia (P(O2) < 10 Torr) were observed. Some cells showed inhibition of outward current in response to hypoxia, whereas other cells showed potentiation. Neurochemical content and electrophysiological responses to hypoxia indicate that these cells are piscine O2-sensitive chemoreceptors.
