Intracellular calcium in mammalian brain cells: fluorescence measurements with quin2. 
Dispersed brain cells from 12-14 day old mouse embryos were loaded with the Ca2+-sensitive fluorescent probe, quin2 and shown to have a resting intracellular Ca2+ concentration ([Ca2+]i) of 158 nM (SE +/- 5) in the presence of 1 mM [Ca2+]o.  When external [Ca2+] was raised from 0 to 1 mM there was an increase of [Ca2+]i of 70 nM; with further additions of Ca to greater than or equal to 10 mM [Ca2+]o the level of [Ca2+]i increased by less than or equal to 25 nM. Releasable intracellular Ca2+ stores, estimated from the increase in [Ca2+] produced by 4-Br A23187 in the absence of extracellular Ca2+, were 24 fmol/10(6) cells.  A small increase in [Ca2+]i could be produced by the mitochondrial inhibitor, carbonyl cyanide m-chlorophenylhydrazone (CCCP).  When extracellular K+ was raised by 10-20 mM, intracellular Ca2+ levels increased from 152 (SE +/- 7) to 204 nM (SE +/- 10).  These K+-induced increases in [Ca2+]i were blocked by verapamil, did not occur in the absence of extracellular Ca2+, and presumably reflect the activation of voltage-dependent Ca2+ channels.  N-methyl-D-aspartic acid (NMDA) evoked an increase in [Ca2+]i, while the kainate-like lathyrus sativus neurotoxin, L-3-oxalyl-amino-2-aminopropionic acid (L-3,2-OAP) did not; this is consistent with previous observations of different and respectively Ca2+-dependent and -independent mechanisms of action of these excitatory amino acids.