Whole-cell voltage-clamp and single channel recording techniques were used to study drug interactions with voltage-dependent K+ channels and N-methyl-D-aspartate (NMDA) and non-NMDA receptor coupled cation channels in cultured hippocampal neurons and fibroblasts transfected with K+ channel genes. Work was focused in five areas: (i) intracellular regulation of ATP-sensitive K+ channels in CNS neurons, (ii) drug effects and intracellular regulation of molecularly defined K+ channel proteins in fibroblast cells transfected with K+ channel genes, (iii) kinetic analysis of low affinity noncompetitive NMDA antagonists, (iv) block of NMDA-activated cation channels by ligands purported to interact with the polyamine modulatory site, and (v) neurosteroid modulation of NMDA receptor responses. Cromakalim activates a K+ current in cultured hippocampal neurons. In inside-out patch recording we demonstrated that the cromakalim-activated K+ channels can be regulated by intracellular ATP and ADP. Similar agents have potential as anticonvulsants, and in the treatment of brain ischemia. The blocking effects of 4-aminopyridine (4-AP) and the peptides charybdotoxin, dendrotoxin and mast cell degranulating peptide (MCDP) were investigated on the NGK1 voltage- dependent K+ channel (Kv 1.2) expressed in fibroblast cells. The potent K+ channel blocking activity of 4-AP and the peptides may contribute to their powerful convulsant activity. Protein kinase A may regulate the Kv1.2 K+ channel. The novel anticonvulsant ADCI (5-aminocarbonyl-5H- dibenzo[a,d]cyclohepten-5,10-imine), a noncompetitive NMDA antagonist structurally related to the dissociative anesthetic dizocilpine and to carbamazepine. Unlike other dissociative anesthetics which cause motor toxicity at low doses, ADCI protects against seizures in animal models at doses that fail to cause motor impairment. In kinetic studies using whole cell voltage clamp techniques in cultured hippocampal neurons, we found the more favorable toxicity profile of ADCI may relate to its ability to block NMDA responses more rapidly than does dizocilpine, Arcaine, a putative competitive antagonist at the polyamine site of the NMDA receptor, and 1,10-diaminodecane and 1,12-diaminododecane, putative inverse agonists at the polyamine site, were found to produce an open channel block of the NMDA receptor, thus complicating the interpretation of their actions at the polyamine site. The muscle relaxant GYKI52466[1- (4-aminophenyl)-4-methyl-7,8-methylenedioxy-5H-2,3-benzodiazepine HC] is a potent antagonist of non-NMDA-type glutamate receptor responses in cultured hippocampal neurons.
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