Drug interactions with voltage-dependent K+ channels and N-methyl-D-aspartate (NMDA) receptor coupled cation channels were studied in cultured hippocampal neurons and in fibroblasts transfected with K+ channel genes using whole-cell voltage-clamp and single channel recording techniques. Work was focused in four areas: (1) kinetic analysis of NMDA antagonism by the novel anticonvulsant drug ADCl; (2) tetrahydroaminoacridine (THA) and arcaine block of NMDA-activated cation channels; (3) characterization of the ion channel stimulated by the K+ channel opener drug cromakalim in CNS neurons; and (4) drug effects on molecularly defined K+ channel proteins in fibroblast cells transfected with K + channel genes. The novel anticonvulsant ADCI is an uncompetitive NMDA antagonist that is structurally related to the dissociative anesthetic MK-801 and to the anticonvulsant carbamazepine. In kinetic studies using whole-cell voltage-clamp techniques in cultured hippocampal neurons, we determined that the more favorable toxicity profile of ADCI may relate to its ability to block NMDA responses more rapidly than does MK-801. THA, a centrally active cholinesterase inhibitor that may provide symptomatic benefit in Alzheimer's disease, was found to produce a voltage-dependent block of NMDA responses in cultured hippocampal neurons and also to reduce the frequency and duration of NMDA-evoked single channel currents in outside-out membrane patches. Because NMDA receptors may play a critical role in cognitive and memory function, THA has the potential to produce undesirable CNS side effects at high doses. Arcaine, a putative competitive antagonist at the polyamine site on the NMDA receptor complex, also produced a voltage-dependent block of NMDA-evoked macroscopic and single channel currents. The K+ channel opener cromakalim has previously been found to activate a K+ current in cultured hippocampal neurons. We have now obtained evidence for the existence of ATP-sensitive K+ channels in hippocampal neurons, and our data indicate that cromakalim and metabolic inhibitors can activate these channels. The effects of the peptide K+ channel blockers charybdotoxin, dendrotoxin and mast cell degranulating peptide (MCDP) were investigated on the NGKl voltage-dependent K+ channel expressed in fibroblast cells. The channels were exquisitely sensitive to blockade by the three peptides when applied from the outside of the membrane, but not from the inside. The potent K+ channel blocking activity of dendrotoxin as elucidated in these studies is likely to contribute to the convulsant activity of the peptides.
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