The A563T variation of the renal epithelial calcium channel TRPV5 among African Americans enhances calcium influx

Abstract

The transient receptor potential cation channel, subfamily V, member 5 (TRPV5) gene, which encodes the Ca(2+) channel in the apical membrane of distal convoluted tubule and connecting tubule of the kidney, exhibits an unusually high frequency of nonsynonymous single nucleotide polymorphisms (SNPs) among African Americans. To assess the functional impacts of the nonsynonymous SNP variations in TRPV5, these variants were analyzed with radiotracer (45)Ca(2+) influx assay and the voltage-clamp technique using Xenopus laevis oocytes. Among the variations tested, including A8V, R154H, A563T, and L712F, the latter two significantly increased TRPV5-mediated Ca(2+) influx. The A563T variant, which exists in African Americans with relative high frequency, exhibited increased Ca(2+) influx at extracellular Ca(2+) from 0.01 to 2 mM despite a lower expression level at the plasma membrane. This variant also exhibited a reduction in Na(+) current as a result of increased sensitivity to extracellular Mg(2+). By substituting threonine-563 (Thr(563)) with serine or valine residue, the bulky side chain of Thr(563) was shown to facilitate Ca(2+) transport, whereas the hydroxyl group of Thr(563) is likely related to Mg(2+) sensitivity. The A563T variant was capable of increasing TRPV5-mediated Ca(2+) influx, even when it was expressed under conditions mimicking heterozygous or compound state with other variants. In conclusion, the A563T variant of TRPV5 significantly increased Ca(2+) influx by affecting the Ca(2+) permeation pathway. Thus the A563T variation in TRPV5 may contribute to the superior ability of renal Ca(2+) conservation in African Americans.