Characterization of ATP-sensitive potassium channels functionally expressed in pituitary GH3 cells

ATP-sensitive K+ (K-ATP) channels have been characterized in pituitary GH, cells with the aid of the patch-clamp technique. In the cell-attached configuration, the presence of diazoxide (100 muM) revealed the presence of glibenclamide-sensitive K-ATP channel exhibition a unitary conductance of 74 pS. Metabolic inhibition induced by 2,4-dinitrophenol (1 mM) or sodium cyanide (300 muM) increased K-ATP channel activity, while nicorandil (100 muM) 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 muM. The activation of phospholipase A, caused by mellitin (1 muM) was found to enhance K-ATP channel activity and further application of aristolochic acid (30 muM) reduced the mellitin-induced increase in channel activity. The challenging of cells with 4,4'-dithiodipyridine (100 muM) also induced K-ATP channel activity. Diazoxide, mellitin and 4,4'-dithiodipyridine activated the K-ATP channels that exhibited similar channel-opening kinetics. In addition, under current-clamp conditions, the application of diazoxide (100 muM) hyperpolarized the membrane potential and reduced the firing rate of spontaneous action potentials. The present study clearly indicates that K-ATP channels similar to those seen in pancreatic beta cells are functionally expressed in GH(3) cells. In addition to the presence of Ca2+-activated K+ channels, K-ATP channels found in these cells could thus play an important role in controlling hormonal release by regulating the membrane potential.