Premium
A novel osmosensitive voltage gated cation current in rat supraoptic neurones
Author(s) -
Liu XiaoHong,
Zhang Wenbo,
Fisher Thomas E.
Publication year - 2005
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.2005.093773
Subject(s) - depolarization , biophysics , supraoptic nucleus , vasopressin , chemistry , oxytocin , osmotic concentration , current (fluid) , patch clamp , plasma osmolality , osmoreceptor , medicine , membrane potential , endocrinology , electrophysiology , biology , biochemistry , engineering , electrical engineering
The magnocellular neurosecretory cells of the hypothalamus (MNCs) regulate water balance by releasing vasopressin and oxytocin as a function of plasma osmolality. Release is determined largely by the rate and pattern of action potentials generated in the MNC somata. Changes in firing are mediated in part by a stretch‐inactivated non‐selective cation current that causes the cells to depolarize when increased osmolality leads to cell shrinkage. We have obtained evidence for a new current that may regulate MNC firing during changes in external osmolality, using whole‐cell patch clamp of acutely isolated rat MNC somata. In internal and external solutions lacking K + , with high concentrations of TEA, and with Na + as the only likely permeant cation, the current appears as a slow inward current during depolarizations and yields a large tail current upon return to the holding potential of −80 mV. Approximately 60% of the MNCs tested (79 out of 134 cells) displayed a large increase in tail current density (from 5.2 ± 0.9 to 10.5 ± 1.4 pA pF −1 ; P < 0.001) following an increase in external osmolality from 295 to 325 mosmol kg −1 . The current is activated by depolarization to potentials above −60 mV and does not appear to depend on changes in internal Ca 2 + . The current is carried by Na + under these conditions, but is blocked by Cs + and Ba 2 + and by internal K + , which suggests that the current could be a K + current under physiological conditions. This current could play an important role in regulating the response of MNCs to osmolality.