Low-voltage-activated Ca2+ currents are generated by members of the CavT subunit family (α1G/H) in rat primary sensory neurons

Recently, two members of a new family of Ca2+ channel alpha 1 subunits, alpha 1G (or CavT.1) and alpha 1H (or CavT.2), have been cloned and expressed. These alpha 1 subunits generate Ba2+ currents similar to the T-type Ca2+ currents present in sensory neurons. Here, we use three methods to investigate whether the T currents of nodosus ganglion neurons are encoded by members of the Ca,T family. PCR detected the presence of mRNA encoding both alpha 1G and alpha 1H, as well as a third highly related sequence, all. In situ hybridizations performed on nodosus ganglia demonstrate a high expression of alpha 1H subunit RNAs. Transfection of nodosus ganglion neurons with a generic antisense oligonucleotide against this new alpha 1 subunit family selectively suppresses the low-voltage-activated Ca2+ current. The antisense oligonucleotide effect increased with time after transfection and reached a maximum 3 d after treatment, indicating a 2-3 d turnover for the alpha 1 proteins. Taken together, these results suggest that the T-type current present in the sensory neurons is mainly attributable to alpha 1H channels. In addition, taking advantage of the high specificity of the antisense ON to the cloned channels, we showed that T-type currents greatly slowed the repolarization occurring during an action potential and were responsible for up to 51% of the Ca2+ entry during spikes. Therefore, the antisense strategy clearly demonstrates the role of low-voltage-activated Ca2+ current in affecting the afterpotential properties and influencing the cell excitability. Such tools should be beneficial to further studies investigating physiological roles of T-type Ca2+ currents.