Immunochemical identification and subcellular distribution of the alpha 1A subunits of brain calcium channels

Abstract

A site-directed anti-peptide antibody (anti-CNA1) directed against the alpha 1 subunit of class A calcium channels (alpha 1A) recognized a protein of approximately 190-200 kDa in immunoblot and immunoprecipitation analyses of rat brain glycoproteins. Calcium channels recognized by anti-CNA1 were distributed throughout the brain with a high concentration in the cerebellum. Calcium channels having alpha 1A subunits were concentrated in presynaptic terminals making synapses on cell bodies and on dendritic shafts and spines of many classes of neurons and were especially prominent in the synapses of the parallel fibers of cerebellar granule cells on Purkinje neurons where their localization in presynaptic terminals was confirmed by double labeling with the synaptic membrane protein syntaxin or the microinjected postsynaptic marker Neurobiotin. They were present in lower density in the surface membrane of dendrites of most major classes of neurons. There was substantial labeling of Purkinje cell bodies, but less intense staining of the cell bodies of hippocampal pyramidal neurons, layer V pyramidal neurons in the dorsal cortex, and most other classes of neurons in the forebrain and cerebellum. Scattered cell bodies elsewhere in the brain were labeled at low levels. These results define a unique pattern of localization of class A calcium channels in the cell bodies, dendrites, and presynaptic terminals of most central neurons. Compared to class B N-type calcium channels, class A calcium channels are concentrated in a larger number of presynaptic nerve terminals implying a more prominent role in neurotransmitter release at many central synapses.