KAINATE ELICITS ELEVATED NUCLEAR CALCIUM SIGNALS IN RETINAL NEURONS VIA CALCIUM-INDUCED CALCIUM-RELEASE

Intracellular Ca2+ was imaged in cultured neonatal rat retinal neurons using the Ca2+-sensitive dye fluo-3 and confocal scanning laser micro scopy. Depolarization via elevation of bath K+ concentration resulted in large cytoplasmic and nuclear Ca2+ signals; responses in the nucleu s exceeded those of the cytoplasm. Glutamate or kainate application el icited the same intracellular pattern of elevated Ca2+ signals. Kainat e stimulation was blocked by the non-NMDA receptor antagonist, 6-cyano -7-nitroquinoxaline-2,3-dione (CNQX), and greatly reduced by removing Ca2+ from the bath and adding ethylene glycol-bis (beta-amino-ethyl et her) N,N,N',N'-tetraacetic acid (EGTA). Kainate was equally effective in eliciting Ca2+ signals when bath Na+ was replaced with equimolar co ncentrations of choline, or in the presence of the NMDA receptor antag onist, 2-amino-5-phosphonovaleric acid (APV). Caffeine treatment signi ficantly reduced the kainate-induced intracellular Ca2+ response. Thes e results suggest that Ca2+ can enter through the kainate receptor of retinal neurons and amplify the Ca2+ signals in the cytoplasm and nucl eus by releasing Ca2+ from intracellular stores.