FIGURE 1.

Channel function of human TRPP3 N-terminal truncation mutants. A, putative membrane topology predicted for TRPP3 (top) and five truncated mutants with indicated positions of the starting amino acid residue (bottom). B, radiolabeled ⁴⁵Ca uptake in X. laevis oocytes expressing TRPP3 wild-type (WT) or mutants at day 3 following RNA injection. Oocytes injected with H₂O were used as a negative control. Data were averaged from three independent experiments. *** indicates p < 0.001. C, representative whole-cell current traces obtained from Xenopus oocytes expressing TRPP3 WT or an indicated truncation mutant, using TEVC. Oocytes were voltage clamped at −50 mV. Data from H₂O-injected oocytes served as a negative control. Currents were measured using the standard Na⁺-containing extracellular solution without (STD) or with (STD+Ca) 5 mm CaCl₂. D, averaged Ca²⁺-activated currents obtained at −50 mV from oocytes expressing TRPP3 WT or an indicated mutant or those injected with H₂O. Currents were averaged from three independent experiments with total numbers of tested oocytes, as indicated. *** indicates p < 0.001. E, representative current-voltage relationship curves obtained using a voltage ramp protocol, as indicated, before (STD) and after (STD+Ca) addition of 5 mm CaCl₂ at the time point marked with a and b, respectively, in C. F, representative immunofluorescence data using oocyte slices, showing expression of TRPP3 WT and indicated truncation mutants.