ON THE ORIGIN OF A SUSTAINED INCREASE IN CYTOSOLIC CA2-CELL CULTURE( CONCENTRATION AFTER A TOXIC GLUTAMATE TREATMENT OF THE NERVE)

A sustained increase of cytosolic Ca2+ concentration, [Ca2+]i, (Ca2+ p lateau) was induced by a 15-min treatment with 50 muM glutamate of cul tured cerebellar granule cells and hippocampal neurons in a Mg2+-free solution. Plateau proved to be insensitive to inhibition of Na(o)+/Ca( i)2+ exchange caused by removal external Na+ in the post-glutamate per iod. A is similar to 10(5)-fold reduction of [Ca2+]o (from 1.5 mM to 2 0 nM) in the post-glutamate period caused in most cells only a slow an d small decrease in [Ca2+]i, although the same low-Ca2+ trial before g lutamate treatment caused in hippocampal cells very quick blockade of spontaneous [Ca2+]i oscillation and a decrease in the basal [Ca2+]i. T he results suggest that the Ca2+ plateau is due to a suppression of th e Ca2+ extrusion from the cell (in particular via Na+/Ca2+ exchange) r ather than from a persistent increase in Ca2+ permeability of neuronal membrane.