ATP-sensitive K+ (KATP) channels have been characterized in pituitary GH3 cells with the aid of the patch-clamp technique. In the cell-attached configuration, the presence of diazoxide (100 μm) revealed the presence of glibenclamide-sensitive KATP channel exhibiting a unitary conductance of 74 pS. Metabolic inhibition induced by 2,4-dinitrophenol (1 mm) or sodium cyanide (300 μm) increased KATP channel activity, while nicorandil (100 μm) had no effect on it. In the inside-out configuration, Mg-ATP applied intracellularly suppressed the activity of KATP channels in a concentration-dependent manner with an IC50 value of 30 μm. The activation of phospholipase A2 caused by mellitin (1 μm) was found to enhance KATP channel activity and further application of aristolochic acid (30 μm) reduced the mellitin-induced increase in channel activity. The challenging of cells with 4,4′-dithiodipyridine (100 μm) also induced KATP channel activity. Diazoxide, mellitin and 4,4′-dithiodipyridine activated the KATP channels that exhibited similar channel-opening kinetics. In addition, under current-clamp conditions, the application of diazoxide (100 μm) hyperpolarized the membrane potential and reduced the firing rate of spontaneous action potentials. The present study clearly indicates that KATP channels similar to those seen in pancreatic β cells are functionally expressed in GH3 cells. In addition to the presence of Ca2+-activated K+ channels, KATP channels found in these cells could thus play an important role in controlling hormonal release by regulating the membrane potential.
The Journal of Membrane Biology – Springer Journals
Published: Dec 1, 2000
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