Electrophysiological properties of heteromeric TRPV4-C1 channels.

We previously reported that TRPV4 and TRPC1 can co-assemble to form heteromeric TRPV4-C1 channels [12]. In the present study, we characterized some basic electrophysiological properties of heteromeric TRPV4-C1 channels. 4α-Phorbol 12,13-didecanoate (4α-PDD, a TRPV4 agonist) activated a single channel current in HEK293 cells co-expressing TRPV4 and TRPC1. The activity of the channels was abrogated by a TRPC1-targeting blocking antibody T1E3. Conductance of the channels was ~95pS for outward currents and ~83pS for inward currents. The channels with similar conductance were also recorded in cells expressing TRPV4-C1 concatamers, in which assembled channels were expected to be mostly 2V4:2C1. Fluorescence Resonance Energy Transfer (FRET) experiments confirmed the formation of a protein complex with 2V4:2C1 stoichiometry while suggesting an unlikeliness of 3V4:1C1 or 1V4:3C1 stoichiometry. Monovalent cation permeability profiles were compared between heteromeric TRPV4-C1 and homomeric TRPV4 channels. For heteromeric TRPV4-C1 channels, their permeation profile was found to fit to Eisenman sequence VI, indicative of a strong field strength cation binding site, whereas for homomeric TRPV4 channels, their permeation profile corresponded to Eisenman sequence IV for a weak field strength binding site. Compared to homomeric TRPV4 channels, heteromeric TRPV4-C1 channels were slightly more permeable to Ca2+ and had a reduced sensitivity to extracellular Ca2+ inhibition. In summary, we found that, when TRPV4 and TRPC1 were co-expressed in HEK293 cells, the predominate assembly type was 2V4:2C1. The heteromeric TRPV4-C1 channels display distinct electrophysiological properties different from those of homomeric TRPV4 channels.