Subtype-selective reconstitution of synaptic transmission in sympathetic ganglion neurons by expression of exogenous calcium channels

Fast cholinergic neurotransmission between superior cervical ganglion neurons (SCGNs) in cell culture is initiated by N-type Ca2+ currents through Ca(v)2.2 channels. To test the ability of different Ca2+-channel subtypes to initiate synaptic transmission in these cells, SCGNs were injected with cDNAs encoding Ca(v)1.2 channels, which conduct L-type currents, Ca(v)2.1 channels, which conduct P/Q-type Ca2+ currents, and Ca(v)2.3 channels, which conduct R-type Ca2+ currents. Exogenously expressed Ca(v)2.1 channels were localized in nerve terminals, as assessed by immunocytochemistry with subtype-specific antibodies, and these channels effectively initiated synaptic transmission. Injection with cDNA encoding Cav2.3 channels yielded a lower level of presynaptic labeling and synaptic transmission, whereas injection with cDNA encoding Ca(v)1.2 channels resulted in no presynaptic labeling and no synaptic transmission. Our results show that exogenously expressed Ca2+ channels can mediate synaptic transmission in SCGNs and that the specificity of reconstitution of neurotransmission (Ca(v)2.1 > Ca(v)2.3 much greater than Ca(v)1.2) follows the same order as in neurons in vivo. The specificity of reconstitution of neurotransmission parallels the specificity of trafficking of these Ca-v channels to nerve terminals.