GLUTAMATE RECEPTOR-MEDIATED CALCIUM-ENTRY IN NEURONS DERIVED FROM P19EMBRYONAL CARCINOMA-CELLS

We have examined the control of calcium elevation by glutamate in neur ons derived from the mouse P19 embryonal carcinoma cell line, Followin g transient exposure to retinoic acid, P19 cells differentiate into ne urons that express both NMDA and non-NMDA glutamate receptor subtypes, Fluorescence videomicroscopy using the indicator fura-2 revealed conc entration-dependent elevation in cytosolic calcium levels with exposur e to NMDA or kainate, Replacement of extracellular sodium with N-methy lglucamine significantly reduced the action of kainate, Exposure to hi gh K+ medium also elicited an elevation of cytosolic calcium in P19 ce lls, which was partially inhibited by the calcium channel antagonist n imodipine. These experiments suggest that the elevation in calcium pro duced by kainate involves the activation of voltage-gated calcium chan nels as a consequence of membrane depolarization, in contrast to direc t calcium entry through NMDA receptor channels. Whole-cell recordings revealed that P19 NMDA receptors were highly permeable to calcium (P-C a/P-Na = 5.6 +/- 0.2), In most cells, channels gated by kainate displa yed low permeability to calcium; the median permeability ratio, P-Ca/P -Na, was 0.053 (range 0.045 to 0.132), Activation of peak currents by NMDA, glycine, and kainate was half-maximal at 24 mu M, 240 nM, and 81 mu M, respectively, In addition, cadmium-sensitive currents through v oltage-gated calcium channels were recorded in P19 cells bathed in bar ium/TEA chloride, Staining with antibodies directed against AMPA recep tor subunits revealed widespread immunoreactivity for anti-GluR-B/C an d anti-GluR-B/D. About half of the P19 cells were stained with antibod ies selective for GluR-D but there was little or no immunoreactivity f or the GluR-A subunit. (C) 1996 Wiley-Liss, Inc.