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Am J Physiol Regul Integr Comp Physiol 265: R1475-R1479, 1993;
0363-6119/93 $5.00
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AJP - Regulatory, Integrative and Comparative Physiology, Vol 265, Issue 6 1475-R1479, Copyright © 1993 by American Physiological Society

ARTICLES

Steady-state osmotic modulation of cationic conductance in neurons of rat supraoptic nucleus

S. H. Oliet and C. W. Bourque
Centre for Research in Neuroscience, Montreal General Hospital, Quebec, Canada.

Whole cell patch-clamp recordings were obtained from isolated rat supraoptic nucleus magnocellular neurosecretory cells (MNCs). Under current clamping, hyperosmolality produced by the addition of 10-30 mM mannitol depolarized each of 25 cells tested. In contrast, reducing fluid osmolality from 295 to 265 mosmol/kgH2O had the reverse effect, hyperpolarizing 18 of 21 MNCs. Voltage-clamp recordings in 43 cells revealed that the effects of hypo- and hyperosmolality, respectively, were caused by decreases and increases in a nonselective cation conductance reversing near -41 mV. Current-voltage analysis in Na(+)-free solution revealed that the reversal potentials of currents elicited by increases and decreases in osmolality both shifted to a value near -90 mV, suggesting that a single ionic conductance is modulated by these stimuli. The relation between cationic conductance and osmolality was specific, sensitive (+2.14%.mosmol-1.kgH2O-1), and well-fit by linear regression (r = 0.96; n = 22 cells) between 275 and 325 mosmol/kgH2O. These results indicate that MNCs express a depolarizing current that is active under steady-state conditions and that the up- or downregulation of this current contributes to the excitation or inhibition of these cells upon acute exposure to hypo- or hyperosmolar conditions.


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