Localization of Ca²⁺Channel Subtypes on Rat Spinal Motor Neurons, Interneurons, and Nerve Terminals

TLDR

Voltage‑dependent Ca²⁺ channels in neuronal compartments mediate influx that integrates synaptic responses, regulates gene expression, and initiates transmission. The study aimed to map the localization of class A–E Ca²⁺ channel α₁ subunits on rat spinal motor neurons, interneurons, and nerve terminals. Antibodies selective for α₁ subunits of classes A–E Ca²⁺ channels were employed to visualize channel distribution. P/Q‑type channels clustered in punctate nerve terminals on motor neuron soma, dendrites, and neuromuscular junctions; N‑type channels appeared on cell surfaces and terminals, co‑expressed with substance P in nociceptive synapses; L‑type and R‑type channels were mainly on soma and proximal dendrites, with class A and B channels showing complementary laminar distribution in the spinal cord.

Abstract

Ca²⁺ channels in distinct subcellular compartments of neurons mediate voltage-dependent Ca²⁺ influx, which integrates synaptic responses, regulates gene expression, and initiates synaptic transmission. Antibodies that specifically recognize the α₁ subunits of class A, B, C, D, and E Ca²⁺ channels have been used to investigate the localization of these voltage-gated ion channels on spinal motor neurons, interneurons, and nerve terminals of the adult rat. Class A P/Q-type Ca²⁺ channels were present mainly in a punctate pattern in nerve terminals located along the cell bodies and dendrites of motor neurons. Both smooth and punctate staining patterns were observed over the surface of the cell bodies and dendrites with antibodies to class B N-type Ca²⁺channels, indicating the presence of these channels in the cell surface membrane and in nerve terminals. Class C and D L-type and class E R-type Ca²⁺ channels were distributed mainly over the cell soma and proximal dendrites. Class A P/Q-type Ca²⁺ channels were present predominantly in the presynaptic terminals of motor neurons at the neuromuscular junction. Occasional nerve terminals innervating skeletal muscles from the hindlimb were labeled with antibodies against class B N-type Ca²⁺ channels. Staining of the dorsal laminae of the rat spinal cord revealed a complementary distribution of class A and class B Ca²⁺ channels in nerve terminals in the deeper versus the superficial laminae. Many of the nerve terminals immunoreactive for class B N-type Ca²⁺ channels also contained substance P, an important neuropeptide in pain pathways, suggesting that N-type Ca²⁺ channels are predominant at synapses that carry nociceptive information into the spinal cord.