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

ATP-sensitive K+ (K-ATP) channels in the human medulloblastoma TE671 cell l ine were characterized by membrane potential assays utilizing a potentiomet ric fluorescent probe, bis-(1,3-dibutylbarbituric acid)trimethine oxonol (D iBAC(4)(3)), and by mRNA analysis. Membrane potential assays showed concent ration-dependent and glyburide-sensitive changes in fluorescence upon addit ion of (-)-cromakalim, pinacidil, diazoxide and P1075. The rank order of po tency for these openers was P1075 > (-)-cromakalim similar to pinacidil > d iazoxide. Additionally, glyburide and glipizide inhibited P1075-evoked resp onses in TE671 cells with half-maximal inhibitory concentrations of 0.22 an d 14 mu M, respectively. The rank order potencies of both openers and inhib itors were similar to those observed in the rat smooth muscle A-10 cell lin e. In contrast, in the rat pancreatic insulinoma RIN-m5F cell line, only di azoxide was effective as an opener. Reverse transcription-polymerase chain reaction (RT-PCR) studies detected sulfonylurea receptors SUR2B and SUR1 mR NA in TE671 cells whereas only SUR2B and SUR1 mRNA were, respectively, dete cted in A-10 and RIN-m5F cells. The inward rectifier Kir6.2 mRNA was detect ed 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 ch annels endogenously expressed in TE671 medulloblastoma resemble those prese nt in the smooth muscle. (C) 1999 Elsevier Science B.V. All rights reserved .