Pharmacological and molecular characterization of ATP-sensitive K + channels in the TE671 human medulloblastoma cell line

Abstract

ATP-sensitive K + (K ATP) channels in the human medulloblastoma TE671 cell line were characterized by membrane potential assays utilizing a potentiometric fluorescent probe, bis-(1,3-dibutylbarbituric acid)trimethine oxonol (DiBAC 4(3)), and by mRNA analysis. Membrane potential assays showed concentration-dependent and glyburide-sensitive changes in fluorescence upon addition of (−)-cromakalim, pinacidil, diazoxide and P1075. The rank order of potency for these openers was P1075>(−)-cromakalim∼pinacidil>diazoxide. Additionally, glyburide and glipizide inhibited P1075-evoked responses in TE671 cells with half-maximal inhibitory concentrations of 0.22 and 14 μM, respectively. The rank order potencies of both openers and inhibitors were similar to those observed in the rat smooth muscle A-10 cell line. In contrast, in the rat pancreatic insulinoma RIN-m5F cell line, only diazoxide was effective as an opener. Reverse transcription–polymerase chain reaction (RT–PCR) studies detected sulfonylurea receptors SUR2B and SUR1 mRNA in TE671 cells whereas only SUR2B and SUR1 mRNA were, respectively, detected in A-10 and RIN-m5F cells. The inward rectifier Kir6.2 mRNA was detected in all three cell types whereas Kir6.1 was detected only in A-10 cells. Collectively, the molecular and pharmacologic studies suggest that K ATP channels endogenously expressed in TE671 medulloblastoma resemble those present in the smooth muscle.