Na⁺‐Activated K⁺ Channels in Rat Supraoptic Neurones

Abstract

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.

Electrophysiological properties of identified oxytocin and vasopressin neurones

“…Both OT and VP neurones also exhibit a Na + ‐dependent, voltage‐dependent persistent K + current consistent with the properties of Slo2.1 (Slick) and Slo2.2 (Slack) K + channels, which structurally belong to the Ca 2+− dependent channel family, K Ca 4.1 (KCNT1) and K Ca 4.2 (KCNT2) . Given their Na + activation and very depolarised half‐activation values (approximately −4 mV), we can speculate that these channels could contribute to the small spike‐activated sAHPs remaining following removal of the larger Ca 2+ ‐dependent AHPs in SON neurones, similar to that found in other neurones expressing these channels.…”

Specificity in the interaction of high-voltage-activated Ca2+ channel types with Ca2+-dependent afterhyperpolarizations in magnocellular supraoptic neurons

“…Furthermore, complete block of HVA Ca 2ϩ channels with Cd 2ϩ drastically inhibits the AHP in both cell types, as has been shown previously. The small remaining AHP after Cd 2ϩ may reflect a Ca 2ϩ -independent K ϩ current, such as voltagegated K ϩ current or the Na ϩ -activated K ϩ current recently reported (Bansal and Fisher 2016).…”

Slick (Kcnt2) Sodium-Activated Potassium Channels Limit Peptidergic Nociceptor Excitability and Hyperalgesia

“…The Slick NeuroMab antibody has been successfully used for immunohistochemistry (IHC) studies. 16,17 After several rinses, secondary antibodies including Alexa Fluor 633 anti-mouse, Alexa Fluor 488 anti-goat, Alexa Fluor 546 anti-chicken, and Alexa Fluor 546 anti-guinea pig were added (1:1000) to PBS containing 3% BSA for 2 hours (Life Technologies, Thermo Fisher Scientific, Waltham,MA, USA). Tissue was then mounted on slides using ProLong Gold Antifade Reagent with 4,6-diamidino-2-phenylindole dihydrochloride (DAPI; Life Technologies).…”