Na(+) -Activated K(+) Channels in Rat Supraoptic Neurones.
The magnocellular neurosecretory cells (MNCs) of the hypothalamus secrete the neurohormones vasopressin and oxytocin. The systemic release of these hormones depends on the rate and pattern of MNC firing and it is therefore important to identify the ion channels that contribute to the electrical behaviour of MNCs. In the present study, we report evidence for the presence of Na(+) -activated K(+) (KN a ) channels in rat MNCs. KN a channels mediate outwardly rectifying K(+) currents activated by the increases in intracellular Na(+) that occur during electrical activity. Although the molecular identity of native KN a channels is unclear, their biophysical properties are consistent with those of expressed Slick (slo 2.1) and Slack (slo 2.2) proteins. Using immunocytochemistry and Western blot experiments, we found that both Slick and Slack proteins are expressed in rat MNCs. Using whole cell voltage clamp techniques on acutely isolated rat MNCs, we found that inhibiting Na(+) influx by the addition of the Na(+) channel blocker tetrodotoxin or the replacement of Na(+) in the external solution with Li(+) caused a significant decrease in sustained outward currents. Furthermore, the evoked outward current density was significantly higher in rat MNCs using patch pipettes containing 60 mm Na(+) than it was when patch pipettes containing 0 mm Na(+) were used. Our data show that functional KN a channels are expressed in rat MNCs. These channels could contribute to the activity-dependent afterhyperpolarisations that have been identified in the MNCs and thereby play a role in the regulation of their electrical behaviour.
Department of Physiology, College of Medicine, University of Saskatchewan, Saskatoon, Saskatchewan, Canada.
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Bansal
Department of Physiology, College of Medicine, University of Saskatchewan, Saskatoon, Saskatchewan, Canada.
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Fisher
D000818:Animals; D002478:Cells, Cultured; D005071:Evoked Potentials / Q000187:drug effects / Q000502:physiology; D008094:Lithium / Q000494:pharmacology; D008297:Male; D009419:Nerve Tissue Proteins / Q000096:biosynthesis; D015221:Potassium Channels / Q000096:biosynthesis / Q000502:physiology*; D000081033:Potassium Channels, Sodium-Activated; D051381:Rats; D012964:Sodium / Q000502:physiology*; D013495:Supraoptic Nucleus / Q000187:drug effects / Q000502:physiology*; D013779:Tetrodotoxin / Q000494:pharmacology
C480493:Kcnt2 potassium channel, rat; D009419:Nerve Tissue Proteins; D015221:Potassium Channels; D000081033:Potassium Channels, Sodium-Activated; C000626167:kcnt1 protein, rat; D013779:Tetrodotoxin; D008094:Lithium; D012964:Sodium
AHP; KNa current; Slack; Slick; magnocellular neurosecretory cells; osmoregulation