Cloning and characterization of α1H from human heart, a member of the T-type Ca2+ channel gene family

Abstract

Voltage-activated Ca2+ channels exist as multigene families that share common structural features. Different Ca2+ channels are distinguished by their electrophysiology and pharmacology and can be classified as either low or high voltage-activated channels. Six α1 subunit genes cloned previously code for high voltage-activated Ca2+ channels; therefore, we have used a database search strategy to identify new Ca2+ channel genes, possibly including low voltage-activated (T-type) channels. A novel expressed sequence-tagged cDNA clone of α1G was used to screen a cDNA library, and in the present study, we report the cloning of α1H (or Ca(v)T.2), a low voltage-activated Ca2+ channel from human heart. Northern blots of human mRNA detected more α1H expression in peripheral tissues, such as kidney and heart, than in brain. We mapped the gene, CACNA1H, to human chromosome 16p13.3 and mouse chromosome 17. Expression of α1H in HEK-293 cells resulted in Ca2+ channel currents displaying voltage dependence, kinetics, and unitary conductance characteristic of native T-type Ca2+ channels. The α1H channel is sensitive to mibefradil, a nondihydropyridine Ca2+ channel blocker, with an IC50 of 1.4 μmol/L, consistent with the reported potency of mibefradil for T-type Ca2+ channels. Together with α1G, a rat brain T- type Ca2+ channel also cloned in our laboratory, these genes define a unique family of Ca2+ channels.