A slow transient potassium current expressed in a subset of neurosecretory neurons of the hypothalamic paraventricular nucleus.
Type I putative magnocellular neurosecretory cells of the hypothalamic paraventricular nucleus (PVN) express a prominent transient outward rectification generated by an A-type potassium current. Described here is a slow transient outward current that alters cell excitability and firing frequency in a subset of type I PVN neurons (38%). Unlike most of the type I neurons (62%), the transient outward current in these cells was composed of two kinetically separable current components, a fast activating, fast inactivating component, resembling an A-type potassium current, and a slowly activating [10-90% rise time: 20.4 +/- 12.8 (SE) ms], slowly inactivating component (time constant of inactivation: tau = 239.0 +/- 66.1 ms). The voltage dependence of activation and inactivation and the sensitivity to block by 4-aminopyridine (5 mM) and tetraethylammonium chloride (10 mM) of the fast and slow components were similar. Compared to the other type I neurons, the neurons that expressed the slow transient outward current were less excitable when hyperpolarized, requiring larger current injections to elicit an action potential (58.5 +/- 13.2 vs. 15.4 +/- 2.4 pA; 250-ms duration; P < 0.01), displaying a longer delay to the first spike (184.9 +/- 15.7 vs. 89.7 +/- 8.8 ms with 250- to 1,000-ms, 50-pA current pulses; P < 0.01), and firing at a lower frequency (18. 7 +/- 4.6 vs. 37.0 +/- 5.5 Hz with 100-pA current injections; P < 0. 05). These data suggest that a distinct subset of type I PVN neurons express a novel slow transient outward current that leads to a lower excitability. Based on double labeling following retrograde transport of systemically administered fluoro-gold and intracellular injection of biocytin, these cells are neurosecretory and are similar morphologically to magnocellular neurosecretory cells, although it remains to be determined whether they are magnocellular neurons.
Luther
J A
JA
Neuroscience Program, Tulane University, New Orleans, Louisiana 70118, USA.
Halmos
K C
KC
Tasker
J G
JG
D015761:4-Aminopyridine / Q000494:pharmacology; D000818:Animals; D004553:Electric Conductivity; D066298:In Vitro Techniques; D008297:Male; D009474:Neurons / Q000502:physiology*; D009490:Neurosecretory Systems / Q000166:cytology / Q000502:physiology*; D010286:Paraventricular Hypothalamic Nucleus / Q000166:cytology / Q000502:physiology*; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D019789:Tetraethylammonium / Q000494:pharmacology; D013997:Time Factors
D019789:Tetraethylammonium; D015761:4-Aminopyridine; D011188:Potassium