Steady-state osmotic modulation of cationic conductance in neurons of rat supraoptic nucleus.
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.
Oliet
S H
SH
Centre for Research in Neuroscience, Montreal General Hospital, Quebec, Canada.
Bourque
C W
CW
D000818:Animals; D002412:Cations / Q000378:metabolism*; D004553:Electric Conductivity; D004594:Electrophysiology; D006706:Homeostasis; D008297:Male; D008353:Mannitol / Q000494:pharmacology; D009474:Neurons / Q000502:physiology*; D009995:Osmosis; D051381:Rats; D011919:Rats, Inbred Strains; D013495:Supraoptic Nucleus / Q000502:physiology*
D002412:Cations; D008353:Mannitol