The Recombinant Human TRPV6 Channel Functions as Ca Sensor in Human Embryonic Kidney and Rat Basophilic Leukemia Cells*

The activation mechanism of the recently cloned human transient receptor potential vanilloid type 6 (TRPV6) channel, originally termed Ca transporterlike protein and Ca transporter type 1, was investigated in whole-cell patch-clamp experiments using transiently transfected human embryonic kidney and rat basophilic leukemia cells. The TRPV6-mediated currents are highly Ca -selective, show a strong inward rectification, and reverse at positive potentials, which is similar to store-operated Ca entry in electrically nonexcitable cells. The gating of TRPV6 channels is strongly dependent on the cytosolic free Ca concentration; lowering the intracellular free Ca concentration results in Ca influx, and current amplitude correlates with the intracellular EGTA or BAPTA concentration. This is also the case for TRPV6-mediated currents in the absence of extracellular divalent cations; compared with endogenous currents in nontransfected rat basophilic leukemia cells, these TRPV6-mediated monovalent currents reveal differences in reversal potential, inward rectification, and slope at very negative potentials. Release of stored Ca by inositol 1,4,5-trisphosphate and/or the sarco/endoplasmic reticulum Ca -ATPase inhibitor thapsigargin appears not to be involved in TRPV6 channel gating in both cell lines but, in rat basophilic leukemia cells, readily activates the endogenous Ca release-activated Ca current. In conclusion, TRPV6, expressed in human embryonic kidney cells and in rat basophilic leukemia cells, functions as a Ca sensing Ca channel independently of procedures known to deplete Ca stores.