Synaptic localization and presynaptic function of calcium channel beta(4)-subunits in cultured hippocampal neurons

Neurotransmitter release is triggered by the influx of Ca2+ into the presyn aptic terminal through voltage gated Ca2+-channels. The shape of the presyn aptic Ca2+ signal largely determines the amount of released quanta and thus the size of the synaptic response, Ca2+-channel function is modulated in p articular by the auxiliary beta -subunits that interact intracellularly wit h the pore-forming alpha (1)-subunit, Using retrovirus-mediated gene transf er in cultured hippocampal neurons, we demonstrate that functional GFP-beta (4) constructs colocalize with the synaptic vesicle marker synaptobrevin I I and endogenous P/Q-type channels, indicating that beta (4)-subunits are l ocalized to synaptic sites. Costaining with the dendritic marker MAPS revea led that the beta (4)-subunit is transported to dendrites as well as axons, The nonconserved amino- and carboxyl-termini of the beta (2)-subunit were found to target the protein to the synapse. Physiological measurements in a utaptic hippocampal neurons infected with green fluorescent protein (GFP)-b eta (4) revealed an increase in both excitatory post-synaptic current ampli tude and paired pulse facilitation ratio, whereas the GFP-beta (4) mutant, GFP-beta (4)(Delta 50-407), which demonstrated a cytosolic localization pat tern, did not alter these synaptic properties. In summary, our data suggest a presynaptic function of the Ca2+-channel beta (4)-subunit in synaptic tr ansmission.