FIGURE 2.

TRPC1 is a pore-forming subunit in heteromeric channel complexes and suppresses the calcium permeability of TRPC3/6/7 channel complexes. A–H, whole-cell recordings are shown of HEK293 cells expressing TRPC3, TRPC6, or TRPC7 alone or in combination with TRPC1 together with M₅R (A–C) or of HEK293 cells co-expressing TRPC5 and TRPC1 or TRPC1 mutant channels with amino acid exchanges from glutamate to glutamine at positions 581 (E581Q) and 582 (E582Q) or both (E581Q/E582Q) in combination with the M₅R (G and H). A–C, typical carbachol-induced IV curves measured in standard bath solution (Na⁺_div+CCh) are displayed. Insets show the slope conductance determined during voltage changes from −50 to −60 mV (−55 mV) and from +50 to +60 mV (+55 mV). Only measurements with inwards currents of −200 ± 10 pA at −60 mV and outward currents of 1 ± 0.02 nA at +60 mV were included in the calculations. nS, nano Siemens. D, analysis of the ratios between outward and inward currents at ±60 mV is shown. E, analysis of the reversal potentials determined during application of 10 mm Ca²⁺ solution in the presence of carbachol is shown. F, analysis of the respective calcium permeabilities is shown. G, current density-voltage relationships of carbachol-induced currents in standard bath solution (Na⁺_div+CCh) and in 10 mm Ca²⁺ solution (Ca²⁺+CCh) are displayed. The arrows indicate the reversal potentials in Ca²⁺ solution in the presence of carbachol. H, shown is analysis of the calcium permeabilities. The numbers over the bars indicate the number of cells measured. I, analysis of Mn²⁺ quenching experiments with fura-2-loaded HEK293 cells expressing recombinant TRPC3 alone and TRPC3/TRPC1 as well as TRPC3/TRPC1^E582Q in the presence of 200 μm extracellular Mn²⁺. Each indicated transfection shows the normalized Mn²⁺ quench rate expressed as percentages over time. Numbers above the bars indicate the number of cells measured of six independent experiments for each indicated transfection. *, p < 0.05; **, p < 0.01; ***, p < 0.001.