Müller Dominik, Hoenderop Joost G J, Vennekens Rudi, Eggert Paul, Harangi Ferenc, Méhes Károly, Garcia-Nieto Victor, Claverie-Martin Felix, Os Carel H van, Nilius Bernd, J M Bindels René
Department of Cell Physiology, University Medical Centre Nijmegen, The Netherlands.
Nephrol Dial Transplant. 2002 Sep;17(9):1614-20. doi: 10.1093/ndt/17.9.1614.
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).
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.
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.
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.
上皮钙通道（ECaC）展现出作为1,25 - 二羟维生素D₃调节的钙（再）吸收的守门人的决定性特性。因此，其最近克隆的人类同源物（ECaC1）可能是与钙流失相关的人类疾病（如特发性高钙尿症（IH））中的关键分子。
对9个患有IH的家族中的57名成员进行了研究。通过测量尿钙排泄进行表型分析，同时适当排除其他潜在疾病。最初，对1号染色体1q23.3 - q24上最近提出的与肾结石相关的高钙尿症位点进行了研究。接下来，对ECAC1基因的所有15个外显子以及起始密码子上游2.9 kb进行直接突变分析。在人胚肾293细胞中异源表达的hECaC1通过膜片钳分析进行表征。
所研究家系的遗传模式与常染色体显性性状一致。单倍型分析未表明1号染色体上的位点起作用。ECAC1基因的编码序列在患病和未患病家族成员之间没有差异。在5'侧翼区域，遇到了三个单核苷酸多态性，但无论所筛查家族成员的患病状况如何都观察到了这些多态性。由于与其他物种相比，假定的孔区域包含四个非保守氨基酸取代，因此对hECaC1进行了膜片钳分析。该分析揭示了ECaC的独特特性，包括高钙选择性、内向整流和钙依赖性失活。
这些结果不支持hECaC1在9个患病家族的IH中起主要作用。然而，由于该疾病的异质性，不能排除ECaC1参与IH的其他亚型，需要进一步研究。hECaC1的电生理特性进一步证实了其在钙（再）吸收中的主要作用。
