PIEZO1 expressed in Xenopus oocytes confers increased current elicited by hypotonic medium and negative pressure activates currents in on-cell membrane patches of WT PIEZO1 and mutant R2488Q. (A) Current-voltage relationship of 2-electrode voltage clamp records from uninjected oocytes or oocytes previously injected with cRNA encoding PIEZO1, before and 14 minutes after bath change to a slightly hypotonic solution (ND-96 diluted 20% with distilled water). (B) On-cell patches were established on surface membranes of uninjected Xenopus oocytes or oocytes previously injected with cRNA encoding WT PIEZO1 or mutants R2488Q or R2456H. Currents were recorded during 250-msec voltage ramps between −100 mV and +100 mV. Representative traces from an uninjected oocyte and an oocyte expressing WT PIEZO1 during pipet application of −25 mm Hg hydrostatic pressure. (C) Bar graph of the magnitidue of the current differences between values recorded at −100 and +100 mV in on-cell patches from (n) uninjected oocytes or oocytes previously injected with cRNAs encoding WT PIEZO1 or the indicated mutants, in voltage ramp experiments such as shown in panel A. At −25 mm hydrostatic pressure, uninjected oocytes differed from oocytes expressing WT PIEZO1 or mutant R2488Q, but not from mutant R2456H (P < .05, Kruskal-Wallis ANOVA with the Dunn post-test).