Figure 1.

Off-response property of the PKD1L3–PKD2L1 channel. (A–C) Human embryonic kidney (HEK)293T cells expressing PKD1L3–PKD2L1 were exposed to an acid stimulus (25 mM citric acid; pH 2.8) for 15 s. (A) Changes in [Ca²⁺]_i after acid exposure, as indicated by the fura-2 ratio with pseudocolour expression. (B,C) Profiles of the [Ca²⁺]_i changes recorded for (B) selected individual cells and (C) average changes recorded among experiments (n=12). Red and black bars indicate acid and ionomycin exposure, respectively. (D–F) Patch-clamp analysis of HEK293T cells expressing PKD1L3–PKD2L1. (D) Whole-cell currents induced after removal of the acid stimulus after initial exposure for various durations. HEK293T cells were exposed to 25 mM citric acid (pH 2.8; red bars) at −60 mV for various durations (1–5 and 15 s). No off-response was induced on treatment with 25 mM citric acid neutralized to pH 7.4 (data not shown). (E) Single-channel currents induced after the removal of the acid stimulus in the outside-out configuration. Profiles recorded (a) during or (b) after acid exposure (red bar) are enlarged in the lower panels. A patch membrane was exposed to an acid (pH 2.5) at −60 mV for 5 s; the basal currents were reduced after acid exposure. (F) A representative current in the inside-out configuration. A patch membrane from PKD1L3–PKD21-expressing cells was exposed to an acid (pH 2.8) for 5 s (red bar) at +60 mV. (G) Inhibition of acid-induced whole-cell currents after acid re-exposure. HEK293T cells expressing PKD1L3–PKD2L1 channels were exposed to an acid (pH 2.5) at −60 mV for 10 s. On induction of a high-magnitude inward current after acid removal, an acid was re-applied for 8 s. Red bars indicate acid exposure.