Functional interaction of TRPP2 and TRPV4 in X. laevis oocytes. (A) Analysis of TRP channel whole-cell currents under voltage clamp (V_c) conditions. Currents were recorded in X. laevis oocytes injected with cRNA encoding TRPP2 and/or TRPV4. Mean currents in Ringer or hypotonic solution are shown. (B) Summary of data acquired in A. Asterisks indicate significant differences in the hypotonicity-induced whole-cell conductance (ΔG) compared with water-injected control oocytes; §, significant difference between bars as indicated (n = 21, 15, 38, and 37, respectively). (C and D) Current-voltage (I–V) relations for oocytes expressing TRPV4 or TRPV4 and TRPP2 (D; n = 7). (E) Increasing the extracellular Ca²⁺ concentration from 1.8 to 18 mM led to a significant increase in whole-cell currents in TRPV4-expressing oocytes. This effect was dramatically augmented in oocytes coexpressing TRPP2. Currents were continuously monitored under voltage clamp conditions (V_c protocol as indicated). (F) Analysis of the relative Ca²⁺ conductance revealed that TRPP2 significantly increased the Ca²⁺ currents (normalized group data, G_Ca²⁺/G_Ringer from E; n = 10, 10, 11, and 7, respectively). Whole-cell currents of oocytes expressing TRPV4 with or without TRPP2 were inhibited by RR with similar potency (see Fig. S2). (G) Analysis of the surface expression of TRPP2 and TRPV4 (n = 4) using an enzyme-linked assay for detection of both channels at the plasma membrane. Asterisks indicate significant differences between black and grey bars, respectively. (H) Representative Western blot of total protein amount of a representative experiment. (I) Summarized data of total protein amounts (n = 4). Error bars represent mean values ± SEM.