A member of the low-voltage-activated calcium channel family was identified in mouse brain by taking advantage of amino acid sequences that have been evolutionary conserved. The identified sequence is similar to that of the recently cloned rat α_1G T-type calcium channel, but there are differences in two insertions in the intracellular connecting loops. Northern blot analysis indicates that its expression is strong in the brain. In situ hybridization revealed that, in mouse brain, the α_1G mRNA is found in the cerebellum, hippocampus, thalamus and olfactory bulb. In contrast to L-type calcium channel currents, I _Ba and I _Ca through the α_1G channel expressed in HEK293 cells did not differ in terms of current density, voltage dependence of current activation, inactivation and deactivation, and speed of recovery from voltage-dependent inactivation. The kinetics of I _Ca inactivation were significantly slower than those of I _Ba. The expressed α_1G channel has a relatively high sensitivity to mibefradil, but is only slightly affected by Ni²⁺.