Synaptic localization and presynaptic function of calcium channel beta 4-subunits in cultured hippocampal neurons.
Neurotransmitter release is triggered by the influx of Ca(2+) into the presynaptic terminal through voltage gated Ca(2+)-channels. The shape of the presynaptic Ca(2+) signal largely determines the amount of released quanta and thus the size of the synaptic response. Ca(2+)-channel function is modulated in particular by the auxiliary beta-subunits that interact intracellularly with the pore-forming alpha(1)-subunit. Using retrovirus-mediated gene transfer in cultured hippocampal neurons, we demonstrate that functional GFP-beta(4) constructs colocalize with the synaptic vesicle marker synaptobrevin II and endogenous P/Q-type channels, indicating that beta(4)-subunits are localized to synaptic sites. Costaining with the dendritic marker MAP2 revealed that the beta(4)-subunit is transported to dendrites as well as axons. The nonconserved amino- and carboxyl-termini of the beta(4)-subunit were found to target the protein to the synapse. Physiological measurements in autaptic hippocampal neurons infected with green fluorescent protein (GFP)-beta(4) revealed an increase in both excitatory post-synaptic current amplitude and paired pulse facilitation ratio, whereas the GFP-beta(4) mutant, GFP-beta(4)(Delta50-407), which demonstrated a cytosolic localization pattern, did not alter these synaptic properties. In summary, our data suggest a pre-synaptic function of the Ca(2+)-channel beta(4)-subunit in synaptic transmission.
Department of Physiology II, University of Tuebingen, Ob dem Himmelreich 7, 72074 Tuebingen, Germany.
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Wittemann
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Mark
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Rettig
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Herlitze
D001483:Base Sequence; D015220:Calcium Channels / Q000737:chemistry / Q000502:physiology*; D002460:Cell Line; D017931:DNA Primers; D006624:Hippocampus / Q000166:cytology / Q000502:physiology*; D006801:Humans; D007150:Immunohistochemistry; D008564:Membrane Potentials; D013569:Synapses / Q000378:metabolism* / Q000502:physiology
D015220:Calcium Channels; D017931:DNA Primers