Distribution of the voltage-dependent calcium channel α1G subunit mRNA and protein throughout the mature rat brain

The molecular identity of a gene which encodes the pore-forming subunit (alpha(1G)) of a member of the family of low-voltage-activated, T-type, voltage-dependent calcium channels has been described recently. Although northern mRNA analyses have shown alpha(1G) to be expressed predominantly in the brain, the detailed cellular distribution of this protein in the central nervous system (CNS) has not yet been reported. The current study describes the preparation of a subunit specific alpha(1G) riboprobe and antiserum which have been used in parallel in situ mRNA hybridization and immunohistochemical studies to localize alpha(1G) in the mature rat brain. Both alpha(1G) mRNA and protein were widely distributed throughout the brain, but variations were observed in the relative level of expression in discrete nuclei. Immunoreactivity for alpha(1G) was typically localized in both the soma and dendrites of many neurons. Whilst alpha(1G) protein and mRNA expression were often observed in cells known to exhibit T-type current activity, some was also noted in regions, e.g. cerebellar granule cells, in which T-type activity has not been described. These observations may reflect differences between the subcellular distribution of channels that can be identified by immunohistochemical methods compared with electrophysiological techniques.