Voltage-gated Ca2+ channels in accessory lobe neurons of the chick
Birds have ten pairs of protrusions, “accessory lobes”, on the lateral sides of the lumbosacral spinal cord. It has been proposed that accessory lobes act as a sensory organ of equilibrium and neurons in accessory lobes transmit sensory information to the motor center. We have reported that cells in chick accessory lobes express functional voltage-gated Na+ and K+ channels and generate action potentials. In this study, we examined properties of voltage-gated Ca2+ channels (VGCCs). The amplitude of voltage-gated Ca2+ channel currents carried by Ca2+ and Ba2+ increased gradually during 10 min rather than showing the usual run-down. The current–voltage relationship of Ba2+ currents was consistent with that of the high-voltage-activated Ca2+ channel. The proportion of Ba2+ currents inhibited by ω-conotoxin GVIA was larger than 80 %, indicating that the major subtype is N type. Amplitudes of tail currents of Ca2+ currents evoked by repetitive pulses at 50 Hz are stable for 1 s. If the major subtype of VGCCs at synaptic terminals is also N type, this property may contribute to the establishment of stable synaptic connections between accessory lobe neurons, which are reported to fire at frequencies higher than 15 Hz, and postsynaptic neurons in the spinal cord.