High Polycystin-2 Calcium Permeability in the Primary Cilium of Renal Epithelial Cells

CANTERO MR, CANTIELLO HF

Congreso; 57th Annual Meeting Biophysical Society; 2013

The primary cilium is a sensory, antenna-shaped organelle, which extends from the center of most eukaryotic cells. The ciliary membrane of renal epithelial cells has a high density of ion channels, including polycystin-2 (TRPP2, PC2), a TRP-type, calcium-permeable cation channel. Here, we determined calcium transport in primary cilia of LLC-PK1 renal epithelial cells. Ciliary membranes were reconstituted in the presence of a calcium chemical gradient (100 mM vs. 10 mM). Calcium-permeable ionic currents with a maximum conductance of 200 pS were observed in 102 from 184 experiments. Experimental data were analyzed by the constant field Goldman-Hodgkin-Katz and absolute rate theory models. The reversal potential (Vrev) of the current-voltage relationship was consistent with a low cation-anion perm-selectivity ratio. Addition of amiloride (0.1 mM, trans), however, completely eliminated the ciliary currents, consistent with the possible PC2 control of calcium permeable multichannel complexes. To confirm calcium transport by PC2, calcium permeable currents were determined by the in vitro translated protein in a reconstitution lipid bilayer system in the presence of a calcium chemical gradient. Single channel calcium currents were consistent with maximum conductance of 159 pS at high positive potentials and 12 pS at negative potentials, respectively. The Vrev obtained from the current-voltage relationship was -30 mV, consistent with strong cation selectivity. The interpretation of the experimental data indicated high calcium permeability by PC2. Calcium transport by PC2 in primary cilia may contribute to its sensory function, in particular the regulation of ciliary structure, and responses to environmental cues in renal epithelial cells.