Developmental changes in cell calcium homeostasis during neurogenesis of the embryonic rat cerebral cortex

We quantified cytoplasmic Ca2+ (Ca-c(2+)) levels in cells dissociated from the embryonic (E) rat cortex during neurogenesis. Dual-recordings by flow c ytometry using calcium- and voltage-sensitive dyes revealed that, at the be ginning of cortical development (E11-12), precursor cells exhibited either low (<100 nM), moderate (similar to 250 nM) or high (>1 mu M) resting Ca-c( 2+) levels and well polarized (-70 mV) or less-polarized (-40 mV) resting m embrane potentials which reflected postmitotic or proliferative stages of t he cell cycle. Ca-c(2+) levels of all cells included a Ca-o(2+) entry compo nent, which was also Mn2+-permeant in actively proliferating precursors. Po stmitotic, but not premitotic, precursors exhibited thapsigargin-sensitive intracellular Ca2+ (Ca-i(2+)) stores, which had similar capacities througho ut neuronal lineage development. Differentiating neurons, but not precursor s expressed Ca-i(2+) stores with ryanodine and caffeine sensitivity and bas eline Ca-c(2+) levels that depended on Na+-Ca-2 exchange activity. Voltage- dependent Ca-o(2+) entry was not detected in precursors, but emerged during neuronal differentiation, with most of the neurons expressing functional L -type Ca2+ channels. Ca2+ imaging of individually immunoidentified cells ac utely recovered in culture confirmed that precursors differentiate into neu rone which stereotypically exhibit Ca-o(2+) entry at the level of the membr ane with increased Ca-i(2+) release mechanisms on Ca-i(2+) stores, Na+-Ca2 exchange activity and expression of voltage-dependent Ca2+ channels.