Preand postsynaptic K⁺ and Ca²⁺ fluxes in area CA1 of the rat hippocampus in vitro: effects of Ni²⁺, TEA and 4-AP

Summary

Pre- and postsynaptic fluxes of Ca²⁺ and K⁺ were determined concurrently in CA1 of the hippocampus in vitro under conditions where synaptic transmission was blocked. The Ca²⁺ entry blocker, Ni²⁺, abolished both pre- and postsynaptic Ca²⁺-influx and reduced presynaptic K⁺-efflux by about 20%. Postsynaptic K⁺-efflux was reduced nearly by 60%. 4-aminopyridine (4-AP) strongly enhanced presynaptic Ca²⁺-influx but only marginally increased Ca²⁺-entry into the postsynaptic neurones. At the same time, total K⁺-efflux from presynaptic sites was increased by about 30% but was unaltered postsynaptically. Finally, tetraethylammonium (TEA) enhanced both pre- and postsynaptic Ca²⁺-influx. Postsynaptic influx was more profoundly affected than presynaptic. Neither pre- nor postsynaptic efflux of K⁺ was altered by TEA. The results indicate a complex balance between inward Ca²⁺ and outward K⁺ currents in CA1 and that this balance may differ pre- and postsynaptically.