bis(1-3-dibutylbarbiturate)trimethine-oxonol and Medulloblastoma

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 (DiBAC4(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 approximately = pinacidil > diazoxide. Additionally, glyburide and glipizide inhibited P1075-evoked responses in TE671 cells with half-maximal inhibitory concentrations of 0.22 and 14 microM, 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.

Topics: Adenosine Triphosphate; Animals; Barbiturates; Cells, Cultured; Cromakalim; Fluorescent Dyes; Fluorometry; Glipizide; Glyburide; Humans; Insulinoma; Isoxazoles; Medulloblastoma; Membrane Potentials; Muscle, Smooth; Parasympatholytics; Potassium Channels; Rats; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger; Tumor Cells, Cultured

A critical component of the drug discovery and development process is the identification of novel pharmacophores. Such discovery efforts are, in general, facilitated by rapid and high-throughput cell-based assays of receptor/ion channel-mediated signaling processes to screen diverse chemical libraries of compounds possessing activator or inhibitor activities at the desired target. The availability of the Fluorometric Image Plate Reader (FLIPR) has made rapid assays of cellular signaling processes feasible by simultaneous kinetics measurement of cell-based fluorescence changes in a 96- or 384-well format. This unit describes the application of the FLIPR in cell-based kinetic assays for measuring membrane potential changes and intracellular calcium dynamics.

Topics: Barbiturates; Biological Assay; Calcium Signaling; Cells, Cultured; Cerebellar Neoplasms; Drug Discovery; Fluorescent Dyes; Fluorometry; Humans; Ion Channels; Isoxazoles; Medulloblastoma; Membrane Potentials