Q- and L-type calcium channels control the development of calbindin phenotype in hippocampal pyramidal neurons in vitro

Cultured immature hippocampal neurons from embryonic 17-day-old rats were u sed to explore activity-dependent regulation of neuronal phenotype differen tiation in the developing hippocampus. The calbindin-D-28k phenotype of the pyramidal neurons appeared during the first 6 days in culture, and was exp ressed by 12% of the cells on day 6. Daily stimulation with 50 mM KCl durin g the first 5 days in vitro increased the number of calbindin-D-28k-positiv e pyramidal neurons without affecting neuronal survival. This effect was pr evented by buffering extracellular Ca2+. Omega-agatoxin-IVA-sensitive Q-typ e and nitrendipine-sensitive L-type voltage-gated Ca2+ channels (VGCCs) car ried Ca2+ currents and Ca2+ influx in immature pyramidal neurons at somata level. Blockade of these channels inhibited calbindin-D-28k phenotype induc ed by 50 mM KCl. Conversely, glutamate-activated Ca2+ channel antagonists d id not affect the KCl-induced calbindin-D-28k phenotype. Chronic blockade o f Q- and/or L-type VGCCs downregulated the normal calbindin-D-28k developme nt of immature pyramidal neurons without affecting neuronal survival, the s omatic area of pyramidal neurons or the number of GABAergic-positive (gamma -aminobutyric acid) interneurons. However, at later developmental stages, Q -type VGCCs lost their ability to control Ca2+ influx at somata level, and both Q- and L-type VGCCs failed to regulate calbindin-D-28k phenotype. Thes e results suggest that Q-type channels, which have been predominantly assoc iated with neurotransmitter release in adult brain, transiently act in syne rgy with L-type VGCCs to direct early neuronal differentiation of hippocamp al pyramidal neurons before the establishment of their synaptic circuits.