Osmoreception in rat supraoptic neurons

The osmotic control of neurohypophysial hormone release is mediated by central and peripheral osmoreceptors which perceive changes in fluid osmolality. The mechanism underlying signal transduction in these structures, however, has remained obscure. Supraoptic neurons, which synthesize and secrete the neurohypophysial hormones, are themselves recognized to be osmoreceptors. Combined electrophysiological and micromorphometric measurements were therefore obtained in acutely isolated rat supraoptic neurons to determine the cellular basis for signal transduction in osmoreception. Osmotically-evoked changes in cell volume and a gadolinium-sensitive cationic conductance were found to be temporally and proportionally related. In agreement, cell-attached patch-clamp recordings revealed the presence of gadolinium-sensitive cationic channels modulated in response to osmotic stimuli. The mean closed time of these channels was found to increase as a function of changes in membrane tension mediated either by external osmotic perturbation, or by application of pressure inside the patch pipette. The ionic selectivity, density, mechanosensitivity, and pharmacological properties of these channels are consistent with an involvement in the mechanism underlying osmosreception in supraoptic neurons