Persistent AMPA receptor stimulation alters [Ca2+]i homeostasis in cultures of embryonic dopaminergic neurons.

The effect of the ionotropic glutamate receptor agonist, AMPA, on intracellular Ca2+ concentrations ([Ca2+]i) was studied in dopaminergic neurons present in primary cultures of ventral tegmental mesencephalon of 14 day rat embryos. Exposure of cells to 10 microM AMPA for 1 min increased [Ca2+]i by 2-3 fold in dopaminergic and other neurons and this response was obliterated within 5 min by superfusion with AMPA-free incubation buffer. In dopaminergic neurons, 1 min or 5 min exposure to 50 microM AMPA increased [Ca2+]i 3 to 5 times over control values. This rise in [Ca2+]i persisted even after a 20 min superfusion with AMPA-free media, whereas, [Ca2+]i in non-dopaminergic neurons was reversed to control values during this time. Preincubation (2 min) of cultured cells with NBQX or the L-type channel blocker, nifedipine, but not with MK-801 blunted the rise of [Ca2+]i in dopaminergic and other neurons. Pretreatment with 2 microM NBQX shifted the dose response curve for AMPA to the right without changing the basal [Ca2+]i. The presence of 10 microM dantrolene, a blocker of Ca2+ release from intracellular stores, did not alter the initial rise of [Ca2+]i elicited by 50 microM AMPA, but prevented the destabilization of Ca2+ homeostasis by facilitating the recovery to normal of basal [Ca2+]i. Exposure to 50 microM AMPA (5 min) caused an irreversible increase of [Ca2+]i in dopaminergic neurons and cell death was manifested by propidium iodide uptake 6-7 h after AMPA exposure.(ABSTRACT TRUNCATED AT 250 WORDS)