Distribution of the voltage-dependent calcium channel alpha(1G) subunit mRNA and protein throughout the mature rat brain

The molecular identity of a gene which encodes the pore-forming subunit (al pha(1G)) of a member of the family of low-voltage-activated, T-type, voltag e-dependent calcium channels has been described recently. Although northern mRNA analyses have shown alpha(1G) to be expressed predominantly in the br ain, the detailed cellular distribution of this protein in the central nerv ous 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 immunohistochemic al studies to localize alpha(1G) in the mature rat brain. Both alpha(1G) mR NA and protein were widely distributed throughout the brain, but variations were observed in the relative level of expression in discrete nuclei. Immu noreactivity for alpha(1G) was typically localized in both the soma and den drites of many neurons. Whilst alpha(1G) protein and mRNA expression were o ften observed in cells known to exhibit T-type current activity, some was a lso noted in regions, e.g. cerebellar granule cells, in which T-type activi ty has not been described. These observations may reflect differences betwe en the subcellular distribution of channels that can be identified by immun ohistochemical methods compared with electrophysiological techniques.