Identification of [3H]P1075 binding sites and P1075-activated K+ currents in ovine choroid plexus cells

This study examined the pharmacological characteristics of binding sites for the potent K+ channel opener [H-3]P1075, as well as the functional effects of P1075 on ionic currents and membrane potential, in ovine choroid plexus (OCP) cells. [H-3]P1075 bound to OCP cells with a K-d of 26 +/- 4 nM and a B-max of 10400 +/- 480 sites/cell. Labelled sites were stereoselective and inhibited by potassium channel openers with a rank order of potency: P1075 > BMS-182264, ((4-[[9-cyanoimino)[(1,2,2-trimlthylpropyl)amino]methyl]amino]benzonitrile) > pinacidil >> nicorandil > diazoxide. The K-ATP channel antagonist glyburide inhibited [H-3]P1075 binding with a K-i of 2 mu M. The presence of K-ATP channels on OCP cells was examined by patch clamp and fluorescent (membrane-potential sensitive dye) techniques. In some cells, P1075 activated an outward potassium current which was blocked by glyburide. P1075 produced a glyburide-sensitive, concentration-dependent, hyperpolarization of OCP cells. Levcromakalim hyperpolarized mon strongly than its 3R,4S enantiomer, BRL 38226 ((3R-trans)-3,4-dihydro-3-hydroxy-2,2-dimethyl-4-(2-oxo-1-pyrrolidinyl)-2H-1-benzopyran-6-carbonitrile) indicating a stereoselective interaction. These data indicate that epithelial OCP cells contain glyburide-sensitive K-ATP channels. (C) 1998 Elsevier Science B.V.