Characterization of ATP-Sensitive Potassium Channels Functionally Expressed in Pituitary GH 3 Cells

Abstract

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 microM) 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 microM) increased KATP channel activity, while nicorandil (100 microM) 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 microM. The activation of phospholipase A2 caused by mellitin (1 microM) was found to enhance KATP channel activity and further application of aristolochic acid (30 microM) reduced the mellitin-induced increase in channel activity. The challenging of cells with 4,4'-dithiodipyridine (100 microM) 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 microM) 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 beta cells are functionally expressed in GH3 cells. In addition to the presence of Ca(2+)-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 Inhibition of Inwardly Rectifying K+Channels by Memantine in Macrophages and Microglial Cells

“…Similar to I K(IR) , the macroscopic K + currents which K ATP channels constitute are noted to be inwardly rectifying [27]. However, diazoxide, an opener of K ATP channels, was not found to reverse MEM-inhibited amplitude of I K(IR) in RAW 264.7 cells.…”

“…However, diazoxide, an opener of K ATP channels, was not found to reverse MEM-inhibited amplitude of I K(IR) in RAW 264.7 cells. Moreover, the pipette solution used for whole-cell recordings contained 3 mM ATP which adequately suppresses K ATP -channel activity [27]. Therefore, it seems unlikely that MEM-mediated inhibition of I K(IR) described herein arises from the suppression of K ATP channels, while this type of K + channels also display an inwardly rectifying property.…”

“…Single-channel conductance of Kir channels was calculated by a linear regression using mean values of current amplitudes measured at different potentials. Open and closed lifetime distributions with or without addition of MEM were fitted with logarithmically scaled bin width [27]. Fits reported here were commonly made with nonlinear, least-squares, curve fitting algorithms [28].…”

The Opening Effect of Pregabalin on ATP‐Sensitive Potassium Channels in Differentiated Hippocampal Neuron–derived H19‐7 Cells

“…When filled with pipette solution, their resistance ranged between 3 and 5 M . Ion currents were recorded with glass pipettes in the whole-cell or the inside-out configuration of the patch-clamp technique, by using an RK-400 patchclamp amplifier (Bio-Logic, Claix, France) (27,28). All of the potentials were corrected for liquid junction potential, a value that would always develop at the tip of the pipette when the composition of the pipette solution was different from that in the bath.…”

<b>Localization of ATP-sensitive K</b>^<b>+</b><b> channel subunits in rat pituitary </b><b>gland </b>

“…ATP-sensitive K + (KATP) channels, discovered originally in cardiac muscle (Noma 1983), have been found ubiquitously distributed in various cells and tissues (Inagaki et al, 1995b), such as pancreatic β-cells (Cook et al, 1988;Ashcroft and Kakei, 1989), pituitary GH3 cells (Wu et al, 2000), skeletal muscle (Allard and Lazdunski, 1993), neurons and glial cells of brain (Zhou et al, 2002;Thomzig et al, 2005), kidney (Hurst et al, 1993;Zhou et al, 2007b;Zhou et al, 2008) and testis (Acevedo et al, 2006;Zhou et al, 2011). KATP channels close at high intracellular ATP concentrations and open at lower concentrations during ischemia (Yokoshiki et al, 1998;Yuan et al, 2004 (Inagaki et al, 1996;Clement et al, 1997).…”