BDNF, NT-3 and NGF induce distinct new Ca2+ channel synthesis in developing hippocampal neurons.
Neurotrophins exert short- and long-term effects on synaptic transmission. The mechanism underlying these forms of synaptic plasticity is unknown although it is likely that intracellular Ca2+ and presynaptic Ca2+ channels play a critical role. Here we show that BDNF, NGF and NT-3 (10-100 ng/mL) exhibit a selective long-term up-regulation of voltage-gated Ca2+ current densities in developing hippocampal neurons of 6-20 days in culture. NGF and NT-3 appear more effective in up-regulating L-currents, while BDNF predominantly acts on non-L-currents (N, P/Q and R). The effects of the three neurotrophins were time- and dose-dependent. The EC50 was comparable for BDNF, NGF and NT-3 (10-16 ng/mL) while the time of half-maximal activation was significantly longer for NGF compared to BDNF (58 vs. 25 h). Despite the increased Ca2+ current density, the neurotrophins did not alter the voltage-dependence of channel activation, the kinetics parameters or the elementary properties of Ca2+ channels (single-channel conductance, probability of opening and mean open time). Neurotrophin effects were completely abolished by coincubation with the nonspecific Trk-receptor inhibitor K252a, the protein synthesis blocker anisomycin and the MAP-kinase inhibitor PD98059, while cotreatment with the PLC-gamma blocker, U73122, was without effect. Immunocytochemistry and Western blotting revealed that neurotrophins induced an increased MAP-kinase phosphorylation and its translocation to the nucleus. The present findings suggest that on a long time scale different neurotrophins can selectively up-regulate different Ca2+ channels. The action is mediated by Trk-receptors/MAP-kinase pathways and induces an increased density of newly available Ca2+ channels with unaltered gating activity.
Baldelli
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P
INFM Research Unit and Department of Neuroscience, I-University of Turin, Corso Raffaello 30, I-10125 Turin, Italy.
Forni
P E
PE
Carbone
E
E
D000818:Animals; D019208:Brain-Derived Neurotrophic Factor / Q000494:pharmacology*; D019256:Cadmium Chloride / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D015220:Calcium Channels / Q000235:genetics / Q000502:physiology*; D003470:Culture Media; D004622:Embryo, Mammalian; D005786:Gene Expression Regulation / Q000187:drug effects / Q000502:physiology*; D006624:Hippocampus / Q000166:cytology / Q000502:physiology*; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D020932:Nerve Growth Factor / Q000494:pharmacology*; D009474:Neurons / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D020933:Neurotrophin 3 / Q000494:pharmacology*; D018408:Patch-Clamp Techniques; D051381:Rats; D017207:Rats, Sprague-Dawley
D019208:Brain-Derived Neurotrophic Factor; D002121:Calcium Channel Blockers; D015220:Calcium Channels; D003470:Culture Media; D020933:Neurotrophin 3; D020932:Nerve Growth Factor; D019256:Cadmium Chloride