Cloning and Characterization of α1H From Human Heart, a Member of the T-Type Ca ²⁺ 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 alpha1 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 alpha1G was used to screen a cDNA library, and in the present study, we report the cloning of alpha1H (or CavT.2), a low voltage-activated Ca2+ channel from human heart. Northern blots of human mRNA detected more alpha1H 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 alpha1H in HEK-293 cells resulted in Ca2+ channel currents displaying voltage dependence, kinetics, and unitary conductance characteristic of native T-type Ca2+ channels. The alpha1H channel is sensitive to mibefradil, a nondihydropyridine Ca2+ channel blocker, with an IC50 of 1.4 micromol/L, consistent with the reported potency of mibefradil for T-type Ca2+ channels. Together with alpha1G, a rat brain T-type Ca2+ channel also cloned in our laboratory, these genes define a unique family of Ca2+ channels.

Molecular Physiology of Low-Voltage-Activated T-type Calcium Channels

“…Atypical currents with similar properties have been reported for SMC isolated from rat portal vein (315) and from the terminal branches of guinea pig mesenteric arteries (291). Quite surprisingly, the human tissue that expresses the most mRNA for Ca v 3.2 is the kidney (90,438). In contrast, both Ca v 3.1 and Ca v 3.3 are predominantly expressed in brain (228,288,289,324).…”

“…In general, the electrophysiological properties of T-type currents recorded from various cell types are similar, but differences have been noted in how they inactivate and in their pharmacology. This heterogeneity can be explained in part by the existence of three T-type channels that are encoded on separate genes (90,228,324).…”

Functional effects of the late sodium current inhibition by AZD7009 and lidocaine in rabbit isolated atrial and ventricular tissue and Purkinje fibre

“…The α-subunit of the T-type calcium channel Cav3.2 is encoded by the CACNA1H gene (Cribbs et al, 1998). The T-type Ca 2+ current (ICa T ) activates at lower potential, i.e.…”

T-type channels-secretion coupling: evidence for a fast low-threshold exocytosis

“…The progress of these studies, however, has been often biased by the lack of highaffinity blockers which limited the analyses to narrow ranges of voltages and, in some cases, may have caused serious underestimates of their role in specific physiological functions (see below). A sharp improvement to this approach was provided by the molecular cloning of three different pore-forming α 1 subunits (α 1G , α 1H , and α 1I also named as Ca v 3.1, Ca v 3.2, and Ca v 3.3, respectively) with biophysical properties similar to the endogenous T-type channels [17,53]. This opened a new era of investigations, particularly for the structure-function studies, which have brought important new insights into the mechanisms of ion selectivity and activation-inactivation coupling [52] (see also [10]).…”