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_v2.2 channels. To test the ability of different Ca²⁺-channel subtypes to initiate synaptic transmission in these cells, SCGNs were injected with cDNAs encoding Ca_v1.2 channels, which conduct L-type currents, Ca_v2.1 channels, which conduct P/Q-type Ca²⁺ currents, and Ca_v2.3 channels, which conduct R-type Ca²⁺ currents. Exogenously expressed Ca_v2.1 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 Ca_v2.3 channels yielded a lower level of presynaptic labeling and synaptic transmission, whereas injection with cDNA encoding Ca_v1.2 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_v2.1 > Ca_v2.3 ≫ Ca_v1.2) 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.