REGULATION BY CALCIUM OF THE TRP CHANNEL POLYCYSTIN-2 (TRPP2)

CANTERO MR, CANTIELLO HF

Boston, Massachusetts, USA

Congreso; 53rd Annual Meeting biophysical Society; 2009

olycystin-2 (PC2, TRPP2) is a member of the TRP (transient receptor potential) superfamily of cation channels that permeates Ca2+. Previously, we showed that PC2 is normally active at intracellularly high Ca2+ concentrations (10-15 mM). Here, we explored the role of physiological concentrations of intracellular Ca2+ in PC2-mediated channel function in reconstituted apical membranes from term human syncytiotrophoblast (hST). Addition of either EGTA (1 mM) or BAPTA (2 mM) to reach low intracellular Ca2+ (<5 nM) at the cytoplasmic side, elicited a complete PC2 channel inhibition. A dose response elicited by addition of increasing cytoplasmic Ca2+ showed that Ca2+ activated PC2 with an apparent half activating concentration of 4.78 nM and a Hill coefficient of ~5. Channel function of the in vitro translated PC2 protein with Ca2+ concentrations of 10-15 mM was non-responsive to lowering cytoplasmic Ca2+ with either EGTA or BAPTA. Our data are consistent with a regulatory role of both cytoplasmic and external Ca2+ in PC2 channel function, which does not involve putative Ca2+-binding sites on the channel protein, but instead external sites to the channel protein.