Cocaine decreases the glycine-induced Cl^- current of acutely dissociated rat hippocampal neurons

The effects of cocaine on glycine-induced Cl^- current (I(GLY)) of single neurons, freshly isolated from the rat hippocampal CA1 area, were studied with conventional whole-cell recording under voltage-clamp conditions. Cocaine depressed I(GLY) in a concentration-dependent manner, with an IC₅₀ of 0.78 mM. Preincubation with 1 mM cocaine alone had no effect on I(GLY), suggesting that resting glycine channels are insensitive to cocaine. The depression of I(GLY) by cocaine was independent of membrane voltage. Internal cell dialysis with 1 mM cocaine failed to modify I(GLY). Because the depression of I(GLY) was noncompetitive, cocaine may act on the glycine receptor-chloride ionophore complex at a site distinct from that to which glycine binds. The cocaine suppression of I(GLY) was unaffected by 1 μM tetrodotoxin and 1 μM strychnine. Blockers of protein kinase C (Chelerythrine), kinase A (N-[2-((p-bromocinnamyl)amino)ethyl]-5-isoquinolinesulfonamide HCl, (H-89)) and Ca-calmodulin-dependent kinase (1-[N,O-bis(5-isoquinolinesulfonyl)-N-methyl-L-tyrosyl]-4-phenylpiperazine (KN-62)) were also ineffective, which suggests that these phosphorylating mechanisms do not modulate cocaine-induced suppressant action on I(GLY). This extracellular, strychnine-independent depression of I(GLY) may contribute to cocaine-induced seizures.