Epithelial Ca(2+) channel (ECAC1) in autosomal dominant idiopathic hypercalciuria.
BACKGROUND
The epithelial Ca(2+) channel (ECaC) exhibits the defining properties for being the gatekeeper in 1,25-dihydroxyvitamin D(3)-regulated Ca(2+) (re)absorption. Its recently cloned human orthologue (ECaC1) could, therefore, represent a crucial molecule in human disorders related to Ca(2+)-wasting such as idiopathic hypercalciuria (IH).


METHODS
Fifty-seven members of nine families with IH were investigated. Phenotyping was performed by measurements of urinary Ca(2+) excretion, while other underlying disorders were appropriately excluded. Initially, the recently suggested locus for kidney stone-associated hypercalciuria on chromosome 1q23.3-q24 was investigated. Next, direct mutation analysis of all 15 exons of the ECAC1 gene and 2.9 kb upstream from the start codon was performed. hECaC1, heterologously expressed in human embryonic kidney 293 cells, was characterized by patch-clamp analysis.


RESULTS
The mode of inheritance in the studied pedigrees is consistent with an autosomal dominant trait. Haplotype analysis did not implicate a role of the locus on chromosome 1. The coding sequence of the ECAC1 gene was not different between the affected and the non-affected family members. In the 5'-flanking region, three single nucleotide polymorphisms were encountered, but these polymorphisms were observed regardless of the affection status of the screened family members. Patch-clamp analysis of hECaC1 was performed as the putative pore region contains four non-conserved amino acid substitutions compared with the other species. This analysis revealed the distinctive properties of ECaC, including a high Ca(2+) selectivity, inward rectification, and Ca(2+)-dependent inactivation.


CONCLUSIONS
These results do not support a primary role for hECaC1 in IH in nine affected families. Because of the heterogeneity of the disease, however, the involvement of ECaC1 in other subtypes of IH cannot be excluded and needs further investigation. The electrophysiological properties of hECaC1 further substantiate its prime role in Ca(2+) (re)absorption.
Department of Cell Physiology, University Medical Centre Nijmegen, The Netherlands.
Dominik
D
Müller
Joost G J
JG
Hoenderop
Rudi
R
Vennekens
Paul
P
Eggert
Ferenc
F
Harangi
Károly
K
Méhes
Victor
V
Garcia-Nieto
Felix
F
Claverie-Martin
Carel H van
CH
Os
Bernd
B
Nilius
René
R
J  M  Bindels
D000293:Adolescent; D000328:Adult; D000368:Aged; D002118:Calcium / Q000652:urine*; D015220:Calcium Channels / Q000235:genetics*; D002128:Calcium Metabolism Disorders / Q000235:genetics* / Q000652:urine; D002648:Child; D002675:Child, Preschool; D002874:Chromosome Mapping; D003062:Codon; D005060:Europe; D005260:Female; D005799:Genes, Dominant; D006801:Humans; D008297:Male; D008875:Middle Aged; D009154:Mutation; D016366:Open Reading Frames; D010375:Pedigree; D010641:Phenotype; D050916:TRPV Cation Channels
D015220:Calcium Channels; D003062:Codon; D050916:TRPV Cation Channels; C492239:TRPV5 protein, human; D002118:Calcium