title: Transient calcium-dependent potassium current in magnocellular neurosecretory cells of the rat supraoptic nucleus.
abstract: 1. Magnocellular neurosecretory neurones were impaled in the supraoptic nucleus of perfused explants of rat hypothalamus. Membrane currents were studied at 35 degrees C using the single-microelectrode voltage-clamp technique. 2. Depolarizing voltage steps applied from -100 mV evoked a transient outward current (TOC) from a threshold of -75 mV. From this potential, the amplitude of the current increased non-linearly with voltage. 3. Following its activation TOC reached a peak within 7 ms and subsequently decayed monotonically with a time constant of 30 ms. This time constant did not vary significantly with voltage between -75 and -55 mV. 4. The TOC showed complete steady-state inactivation at potentials positive to -55 mV. Inactivation was removed by hyperpolarization, with a mid-point near -80 mV. The removal of inactivation followed a complex time course with distinct fast (tens of milliseconds) and slow (hundreds of milliseconds) components. 5. Tail current measurements revealed that the TOC equilibrium potential (ETOC) lies near -97 mV in the presence of 3 mM [K+]o. Increasing [K+]o caused a decrease of TOC amplitude and a shift in ETOC of 57 mV/log [K+]o. The TOC is therefore predominantly a K+ current. 6. The TOC was unaffected by tetraethylammonium (up to 12 mM) but was reversibly reduced by 4-aminopyridine (ca. 50% block at 1.0 mM) and dendrotoxin (ca. 50% block at 4 nM). 7. The TOC was strongly inhibited (greater than 70%) by adding Co2+ or Mn2+ (1-3 mM) or Cd2+ (50-400 microM) to Ca-containing solutions, or by removal of Ca2+ from the perfusate. These effects were not accompanied by detectable changes in threshold voltage. The amplitude of TOC was also depressed by the organic Ca2+ channel blocker methoxyverapamil (D600). Finally replacement of Ca2+ by Ba2+ in the perfusate completely and reversibly abolished the TOC. 8. These findings suggest that neurosecretory neurones of the rat supraoptic nucleus display a transient K+ current which is strongly dependent on the presence of external Ca2+. The possible role of this current is briefly discussed.
authors: Department of Pharmacology, School of Pharmacy, University of London.
authors: C W
authors: CW
authors: Bourque
mesh_terms: D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D005260:Female; D066298:In Vitro Techniques; D007473:Ion Channels / Q000187:drug effects / Q000502:physiology*; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D009490:Neurosecretory Systems / Q000502:physiology*; D011188:Potassium / Q000502:physiology*; D051381:Rats; D011919:Rats, Inbred Strains; D013495:Supraoptic Nucleus / Q000502:physiology*; D013779:Tetrodotoxin / Q000494:pharmacology; D013997:Time Factors
chemical_list: D002121:Calcium Channel Blockers; D007473:Ion Channels; D013779:Tetrodotoxin; D011188:Potassium; D002118:Calcium