Electrophysiological and Pharmacological Characterization of the KATP Channel Involved in the K+-Current Responses to FSH and Adenosine in the Follicular Cells of Xenopus Oocyte

Abstract

Abstract:The follicular cells surrounding Xenopus oocyte under voltage clamp produce K + -current responses to follicle-stimulating hormone (FSH), adenosine (Ade), and intracellularly applied cAMP. We previously reported that these responses are suppressed by the stimulation of P2Y receptor through phosphorylation by PKC presumably of the ATP-sensitive K + (K ATP ) channel. This channel comprises sulfonylurea receptors (SURs) and K + ionophores (Kirs) having differential sensitivities to K + channel openers (KCOs) depending on the SURs. To characterize the K + channels involved in the FSH-and Ade-induced responses, we investigated the effects of various KCOs and SUR blockers on the agonist-induced responses. The applications of PCO400, cromakalim (Cro), and pinacidil, but not diazoxide, produced K + -current responses similar to the FSH-and Ade-induced responses in the magnitude order of PCO400 > Cro >> pinacidil in favor of SUR2A. The application of glibenclamide, phentolamine, and tolbutamide suppressed all the K + -current responses to FSH, Ade, cAMP, and KCOs. Furthermore, both the FSH-and Ade-induced responses were markedly augmented during the KCO-induced responses, or vice versa. The I-V curves for the K + -current responses induced by Cro, Ade, and FSH showed outward rectification in normal [K + ] o , but weak inward rectification in 122 mM [K + ] o . Also, stimulations of P2Y receptor by UTP or PKC by PDBu markedly depressed the K + -current response to KCOs in favor of Kir6.1, as previously observed with the responses to FSH and Ade. These results suggest that the K + -current responses to FSH and Ade may be produced by the opening of a novel type of K ATP channel comprising SUR2A and Kir6.1.

The Endogenous Cannabinoid Anandamide Inhibits Cromakalim-Activated K+Currents in Follicle-EnclosedXenopusOocytes

“…Subunit identification of endogenous K ATP channels in follicular cells remains currently unknown. A recent study suggested that a novel type of Kir6.1/SUR2A combination comprises endogenous K ATP channels (Fujita et al, 2007 For many years, Xenopus oocytes have served as a model system for studying intricate mechanisms of follicle maturation and cell cycle control (Brown, 2004). In vivo, stage VI immature oocytes are physiologically arrested in the first meiotic prophase at the G 2 /M border, and they resume meiosis when gonadotropins stimulate surrounding follicle cells.…”

Functional and molecular identification of a TASK-1 potassium channel regulating chloride secretion through CFTR channels in the shark rectal gland: implications for cystic fibrosis

“…Chromanol 293b, an inhibitor of slow delayed rectifier K ϩ current (IKs) (3, 16) had minimal effect. Tolbutamide and phentolamine, inhibitors of K ATP channels (21), and charybdotoxin, which acts on BK CA and K V channels (48,66), had no effects. Although the published K i of charybdotoxin is 0.5 nM and the concentration we used was 50 nM, 100-fold above the K i , this concentration of charybdotoxin would be insufficient to Fig.…”

Role of potassium channels in female reproductive system

“…Typical K ATP channels consist of an inwardrectifier K + ionophore (Kir6.x) and a sulfonylurea receptor (SURx); there are 2 Kir6.x isoforms (Kir6.1 and 6.2), and 3 SUR isoforms (SUR1, SUR2A, and SUR2B). Although 6 combinations of Kir6.x and SURx can be formed, only 4 types of K ATP channel have been reported: those found in pancreas β-cells (SUR1/Kir6.2), cardiac and skeletal muscles (SUR2A/Kir6.2), smooth muscles (SUR2B/Kir6.2), and vascular smooth muscles (SUR2B/Kir6.1) [ 22 ]. Of these, only Kir6.1/SUR2B is detected in the corpus luteum of the ovary and myometrium of the rat, while the placenta expresses Kir6.1 with SUR1 and SUR2B [ 23 ].…”