Electrophysiologic characteristics of the Ca-permeable channels, ECaC and CaT, in the kidney

To investigate the molecular mechanism of Ca transport in the kidney, we ha ve isolated Ca-permeable channels, rECaC (rat ECaC) and mCaT (mouse CaT1), from rodent kidney, which are recently reported as Ca-transporting proteins . RT-PCR suggested the presence of CaT1 in medullary tubules. It showed 67% homology with rECaC constructing a family. Whole cellular currents in Chin ese hamster ovary (CHO) cells were measured by patch clamp. Expression of b oth proteins exhibited a similar large cation current, a high permeability to Ca, a time-dependent rapid inactivation, and a "run-down." When the pipe t contained EGTA, the inactivation and the run-down did not occur. Addition of db-cAMP activated and following rp-CAMPS recovered the mCaT-induced cur rent significantly, whereas no influence was observed in the rECaC-induced one. We conclude that ECaC and CaT are a molecular family of ion channel wi th similar characteristics, contributing Ca transport in the kidney, (C) 20 00 Academic Press.