Journal of Neurophysiology, Vol 64, Issue 5 1361-1367, Copyright © 1990 by APS

ARTICLES

Suppression by extracellular K+ of N-methyl-D-aspartate responses in cultured rat hippocampal neurons

S. Ozawa, M. Iino and K. Tsuzuki
Department of Physiology, School of Medicine, Gunma University, Japan.

1. The effects of increasing K+ concentration in Mg2(+)-free extracellular solution on N-methyl-D-aspartate (NMDA)-induced current were studied in cultured rat hippocampal neurons with the use of the whole-cell and outside-out configurations of the patch-clamp technique. 2. When the K+ concentration in the external solution was increased by replacement of Na+ with isomolar K+, the amplitude of the NMDA-induced current decreased in a concentration-dependent manner. The effect of K+ was almost saturated at 100 mM, when the NMDA response was reduced to 12% of that in K(+)-free, 150 mM Na+ solution. Increasing the external K+ concentration did not affect either the kainate- or quisqualate-induced current in these experimental conditions. 3. Increase in the external K+ concentration reduced the NMDA-induced current almost equally over the whole range of membrane potential tested (-60-30 mV). The reversal potential of the NMDA-induced current was not significantly shifted by the replacement of Na+ with K+. 4. A rise in the external K+ concentration to 100 mM did not reduce the single-channel conductance of the NMDA channel, whereas it reduced the mean open time to about two-thirds of that in the control external solution. 5. The suppressed activation of the NMDA receptor channel in high-K+ environments may have a functional significance to alleviate entry of toxic Ca2+ into neurons of the CNS in pathological conditions such as hypoxia and ischemia.

This article has been cited by other articles:

				J. Makarova, J. M. Ibarz, S. Canals, and O. Herreras A Steady-State Model of Spreading Depression Predicts the Importance of an Unknown Conductance in Specific Dendritic Domains Biophys. J., June 15, 2007; 92(12): 4216 - 4232. [Abstract] [Full Text] [PDF]

				J. W. Xu and M. M. Slaughter Large-Conductance Calcium-Activated Potassium Channels Facilitate Transmitter Release in Salamander Rod Synapse J. Neurosci., August 17, 2005; 25(33): 7660 - 7668. [Abstract] [Full Text] [PDF]

				D. Jabaudon, M. Scanziani, B. H. Gahwiler, and U. Gerber Acute decrease in net glutamate uptake during energy deprivation PNAS, May 9, 2000; 97(10): 5610 - 5615. [Abstract] [Full Text] [PDF]