Figure 3—figure supplement 1.

(A) The fabricated pressure probe was calibrated with hydrostatic pressure by reducing the submersion depth stepwise (inset, 1mmH₂O = 9.8 Pa), which demonstrated good linearity. (B) The pressure probes were calibrated against combinations of the capillary inner diameter and the ionic composition of the bath medium. The probes were displaced stepwise (1.27mmH₂O = 12.45 Pa, dotted line) and the histogram of pressure changes is shown. No dependence on the configurations is observed. (C–D) Calculations of membrane deformation on the piezoresistive sensing element. Colors represent different membrane thickness. (C) The numerical results are compared against analytical solutions for the deformation at the membrane center. (Inset) A selected solution is shown for a 5 µm membrane under 250 Pa pressure. The corresponding volume changes are shown in (D) and the volume of a 200 µm diameter sphere is plotted in dotted line as a reference. (E) Calculations of diffusive mixing between endolymph and capillary filling after puncturing. Their initial ionic concentrations are C₀ and 0, respectively. The mean ionic concentration inside the vesicle C decreases over time t at a rate depending on the capillary inner diameter d. (Inset) Selected solutions are shown for d = 5, 15 µm in the first 5 min. (F) Stages in an otic vesicle pressure measurement. Upper: zooming into the first 1.5 min. I: the tip was placed near the vesicle. The hydrostatic pressure was used as the baseline. II: after puncturing, the pressure built up gradually. III: after reaching a plateau, the pressure fluctuated around a mean value. This value was taken as the measurement result. IV: Upon withdrawing the tip from the vesicle, the pressure dropped to the base line, proving that the probe had been sensing the hydrostatic pressure in the enclosed domain.