Glutamate‐induced increase in intracellular Ca2+ concentration in isolated hippocampal neurones

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Abstract
A system for real‐time quantitative monitoring of intracellular free calcium ion concentration ([Ca2+]i) on a single cell basis was developed by the combination of a fluorescent Ca2+ indicator fura‐2, a fluorescence microscope, a video‐camera and photometrical devices. It was applied to rat individual hippocampal neurones under culture for detection of L‐glutamate‐induced alterations in the [Ca2+]i level. L‐Glutamate (0.01–100 μM) induced a dose‐dependent elevation of the [Ca2+]i. The [Ca2+]i in the rat hippocampal neurone was found to be around 30 nM in the resting state, and was increased up to 500 nM by the application of 100 μM L‐glutamate. N‐methyl‐D‐aspartate, kainate and quisqualate in a concentration of 10 μM also increased the [Ca2+]i level in the same single neurone, but their efficacy varied between individual cells. The L‐glutamate‐induced [Ca2+]i elevation was abolished after removal of extracellular Ca2+ and was much reduced by Mg2+ (3 mM). The increase was, however, still observed in a Na+‐free medium. The L‐glutamate‐induced [Ca2+]i elevation was not affected substantially after treatment with nitrendipine (10 μM) which blocked the increase in [Ca2+]i induced by an isotonic high KCl‐medium (50 mM). The present results suggest that the L‐glutamate‐induced [Ca2+]i elevation in the hippocampal neurone is due to an influx of Ca2+ through both L‐glutamate receptor‐coupled and voltage‐sensitive ionic channels.