Cloning and Characterization of α1H From Human Heart, a Member of the T-Type Ca 2+ Channel Gene Family

Abstract

Abstract —Voltage-activated Ca 2+ channels exist as multigene families that share common structural features. Different Ca 2+ 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 Ca 2+ channels; therefore, we have used a database search strategy to identify new Ca 2+ 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 Ca 2+ 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 Ca 2+ channel currents displaying voltage dependence, kinetics, and unitary conductance characteristic of native T-type Ca 2+ channels. The α1H channel is sensitive to mibefradil, a nondihydropyridine Ca 2+ channel blocker, with an IC 50 of 1.4 μmol/L, consistent with the reported potency of mibefradil for T-type Ca 2+ channels. Together with α1G, a rat brain T-type Ca 2+ channel also cloned in our laboratory, these genes define a unique family of Ca 2+ channels.