A novel large-conductance Ca(2+)-activated potassium channel and current in nerve terminals of the rat neurohypophysis

Wang, Gang, Thorn, Peter and Lemos, Jose R. (1992) A novel large-conductance Ca(2+)-activated potassium channel and current in nerve terminals of the rat neurohypophysis. Journal of Physiology, 457 : 47-74.

Author Wang, Gang
Thorn, Peter
Lemos, Jose R.
Title A novel large-conductance Ca(2+)-activated potassium channel and current in nerve terminals of the rat neurohypophysis
Journal name Journal of Physiology
Publication date 1992-11
Sub-type Article
Volume number 457
ISSN 0022-3751; 1469-7793
Start page 47
End page 74
Total pages 28
Place of publication Oxford
Publisher Blackwell for the Physiological Society
Language eng
Subject 320300 Medical Biochemistry and Clinical Chemistry
Abstract 1. Nerve terminals of the rat posterior pituitary were acutely dissociated and identified using a combination of morphological and immunohistochemical techniques. Terminal membrane currents were studied using the 'whole-cell' patch clamp technique and channels were studied using inside-out and outside-out patches. 2. In physiological solutions, but with 7 mM 4-aminopyridine (4-AP), depolarizing voltage clamp steps from different holding potentials (-90 or -50 mV) elicited a fast, inward current followed by a slow, sustained, outward current. This outward current did not appear to show any steady-state inactivation. 3. The threshold for activation of the outward current was -30 mV and the current-voltage relation was 'bell-shaped'. The amplitude increased with increasingly depolarized potential steps. The outward current reversal potential was measured using tail current analysis and was consistent with that of a potassium current. 4. The sustained potassium current was determined to be dependent on the concentration of intracellular calcium. Extracellular Cd2+ (80 microM), a calcium channel blocker, also reversibly abolished the outward current. 5. The current was delayed in onset and was sustained over the length of a 150 ms-duration depolarizing pulse. The outward current reached a peak plateau and then decayed slowly. The decay was fitted by a single exponential with a time constant of 9.0 +/- 2.2 s. The decay constants did not show a dependence on voltage but rather on intracellular Ca2+. The time course of recovery from this decay was complex with full recovery taking > 190 s. 6. 4-AP (7 mM), dendrotoxin (100 nM), apamin (40-80 nM), and charybdotoxin (10-100 nM) had no effect on the sustained outward current. In contrast Ba2+ (200 microM) and tetraethylammonium inhibited the current, the latter in a dose-dependent manner (apparent concentration giving 50% of maximal inhibition (IC50) = 0.51 mM). 7. The neurohypophysial terminal outward current recorded here corresponds most closely to a Ca(2+)-activated K+ current (IK(Ca)) and not to a delayed rectifier or IA-like current. It also has properties different from that of the Ca(2+)-dependent outward current described in the magnocellular neuronal cell bodies of the hypothalamus. 8. A large conductance channel is often observed in isolated rat neurohypophysial nerve terminals. The channel had a unit conductance of 231 pS in symmetrical 150 mM K+.
Keyword LARGE UNITARY CONDUCTANCE
ANTERIOR-PITUITARY CELLS
K+ CHANNELS
HIPPOCAMPAL-NEURONS
SKELETAL-MUSCLE
TETRAETHYLAMMONIUM BLOCKADE
INTRACELLULAR CALCIUM
CHARYBDOTOXIN BLOCK
SUPRAOPTIC NUCLEUS
ACTION-POTENTIALS
Q-Index Code C1
Q-Index Status Provisional Code
Institutional Status UQ

Document type: Journal Article
Sub-type: Article
Collection: School of Biomedical Sciences Publications
 
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