Premium
Single‐channel Activity in Cultured Cortical Neurons of the Rat in the Presence of a Toxic Dose of Glutamate
Author(s) -
Backus Kurt Harald,
Trube Gerhard
Publication year - 1993
Publication title -
european journal of neuroscience
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.346
H-Index - 206
eISSN - 1460-9568
pISSN - 0953-816X
DOI - 10.1111/j.1460-9568.1993.tb00483.x
Subject(s) - glutamate receptor , biophysics , chemistry , extracellular , nmda receptor , glutamic acid , conductance , intracellular , membrane potential , ion channel , bursting , biochemistry , amino acid , biology , neuroscience , receptor , mathematics , combinatorics
Rat cortical neurons grown in cell culture were exposed to 500 μM glutamate for 5 min during continuous current recording from cell‐attached patches. The Ca 2+ ‐dependence and ion selectivity of the membrane channels activated during and after glutamate application were studied in inside‐out patches. Glutamate blocked spontaneous action potential firing. In 77% of the experiments glutamate activated several types of ion channels indirectly, i.e. via a change of cytoplasmic factors. Channel activity did not disappear after removing glutamate from the bath. A K + channel requiring intracellular calcium ([Ca 2+ ] i ) was activated in 44% of the experiments (conductance for inward currents in cell‐attached patches 118 ± 6 pS;‘BK channel'). Another Ca 2+ ‐dependent channel permeable for Cl ‐ (conductance for outward currents in cell‐attached patches 72±17 pS), acetate and methanesulphonate appeared in 26% of the patches. Other K + channels of smaller conductance were infrequently observed. During and after glutamate application the activity of the BK channel showed an initial increase followed by a transient decay and a second rise to a plateau, probably reflecting a similar time course of changes in [Ca 2+ ] i . Both phases of increasing channel activity required the presence of extracellular Ca 2+ suggesting that [Ca 2+ ] i was mainly increased by Ca 2+ influx. The N ‐methyl‐ d ‐aspartate (NMDA) antagonists dizocilpine (MK‐801, 10 μM) and dl ‐2‐amino‐5‐phosphonovaleric acid (AP5; 100 μM), added within 5 min after glutamate application, stopped BK channel activity and restored the spontaneous action potential firing. We conclude that the influx of Ca 2+ through NMDA receptor channels causes a strong activation of Ca 2+ ‐dependent K + channels, which is likely to result in pronounced loss of intracellular K + . NMDA receptor channels seem to remain active for a long time (>10 min) after the end of glutamate application.