Differential roles of KIR channel and Na+/K+-pump in the regulation of extracellular K+ accumulation in rat hippocampus.

D’Ambrosio R, Gordon D.S., and Winn H.R. Journal of Neurophysiology (2002) Vol 87: 87-102.

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Controlling neuronal firing reveals the underlying activity of the K+-buffering mechanisms in situ. Stimulating electrode was placed in CA2 stratum radiatum. Simultaneous K+ activity recordings and field recordings were performed during 0.05 Hz and 3 Hz antidromic stimulation in normo-excitable slices.

A) The time course of the extracellular K+ accumulation obtained in the presence of freely firing neurons, in the absence of kynurenic acid. Representative samples of the neuronal field response at different time points during the stimulation protocol are illustrated at the top. Notice that the synaptic drive and the amplitude of the recurrent population spike varied throughout the protocol.

B) The time course of the extracellular K+ accumulation obtained in the presence of kynurenic acid to prevent recurrent excitation. Representative samples of the neuronal field response at different time points during the stimulation protocol are illustrated at the top. Only the antidromic spike was observed upon stimulation. Notice that the amplitude of the antidromic population spike remained constant throughout the protocol. The time course of the extracellular K+ accumulation obtained in the absence of kynurenic acid is shown superimposed as a dotted line.

C) Role of Na+/K+-pump in the regulation of extracellular K+ during CA3 pyramidal cell firing as revealed by the application of dihydroouabain. The pump affect baseline [K+]o, the rate of recovery during high frequency stimulation and the undershoot at the end of it.

D) Role of glial KIR channels in the regulation of extracellular K+ during CA3 pyramidal cell firing as revealed by the application of barium. Glial KIR channels affect baseline [K+]o, do not affect the rate of recovery during high frequency stimulation, and contribute to buffer the undershoot at the end of it.