Regulation by Calcium of Polycystin-2 (TRPP2) and Hetero-Complexes with TRPC1

CANTERO MR; CANTIELLO HF

Congreso; 54th Annual Meeting Biophysical Society. “; 2010

Polycystin-2 (PC2, TRPP2) and the canonical TRPC1 are TRP superfamily members that act as non-selective cation channels, with multiple subconductance states and permeability to calcium. Recent studies from our laboratory (Zhang et al., Hum Mol Genet, 2009) indicated that both channels, form homo and hetero-tetramers with distinct functional properties. Both TRP channels are implicated in calcium transport and signaling events, therefore, their regulation by calcium is relevant to their role in cell function. Here we studied the effect of cytoplasmic and external calcium on the regulation of PC2, TRPC1 and PC2/TRPC1, channel function. Lowering cytoplasmic calcium (0.3 nM) with either BAPTA or EGTA inhibited PC2 channel function. This inhibition was extrinsic to the channel complex, and was dependent of external calcium concentrations. Titration of cytoplasmic calcium recovered PC2 channel activity, with a Hill coefficient of 5 and an apparent affinity constant of 1-5 nM. The addition of either BAPTA (2 mM) or EGTA (1 mM) to TRPC1 to lower cytoplasmic calcium concentrations did not inhibit the current (single channel conductance) mediated by the TRPC1 homo-tetrameric channel. In contrast, low calcium decreased TRPC1's mean open probability by 50%. In addition, low cytoplasmic calcium did not inhibit PC2 channel function when hetero-complexed with TRPC1. These data suggest that the formation of structural hetero-complexes between PC2 and TRPC1 confers important regulatory changes to either channel's function, such as the sensory response to cytoplasmic calcium concentrations, thus providing functional diversity to their channel properties in endogenous environments such as the primary cilium or the plasma membrane, where they locate.