Pressure and ultrasound activate mechanosensitive TRAAK K + channels through increased membrane tension

Figures

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  Figure 1.. Pressure stimulation activates TRAAK and MscS channels. A. Macroscopic currents (upper) from a TRAAK-containing patch in response to a pressure step protocol (lower, Vhold = 0 mV, Ptest = 0 to −25 mmHg, ΔP = −2.5 mmHg). B. Normalized current-pressure relationships from 7 TRAAK-containing patches. C. Macroscopic currents (upper) from a MscS-containing patch in response to a pressure step protocol (lower, Vhold = −60 mV, Ptest = 0 to −14 mmHg, ΔP = −2 mmHg). D. Normalized current-pressure relationships from 8 MscS-containing patches.

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  Figure 2.. Quantification of TRAAK channel activation by membrane tension. A. (Right) Macroscopic currents from a TRAAK-containing patch in response to a pressure step protocol (Vhold = 0 mV, Ptest = 0 to −6 mmHg, ΔP = −0.5 mmHg, 1 mmHg steps displayed). (Left) Fluorescent images of the patched membrane at the time of maximum current response during each pressure step. Fits for patch radius (red line), measured pressures, and calculated tensions are shown in each image. B. Normalized current-tension relationships for 5 TRAAK-containing patches. Global fit to a Boltzmann sigmoidal with 95% confidence intervals is shown. (T50 = 4.7 ± 0.2 mN/m, n = 5 patches). C. Normalized current-tension relationships for 4 MscS-containing patches. Global fit to a Boltzmann sigmoidal with 95% confidence intervals is shown (T50 = 3.7 mN/m ± 0.2 mN/m, n = 4 patches). D. Overlaid fits comparing TRAAK and MscS response to tension.

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  Figure 3.. Ultrasound stimulation activates TRAAK and MscS channels. A. Schematic of recording setup for ultrasound stimulation during simultaneous patch recording and imaging. A 3.5 MHz ultrasound transducer is mounted into a custom 3D printed recording dish and patched membranes are positioned at the position of maximum ultrasonic power. B. Macroscopic currents from a TRAAK-containing patch in response to an ultrasound step protocol (Vhold = 0 mV, transducer driving voltage = 0-1 V, Δ driving voltage = 100mV, 100mV intervals displayed with measured power in W/cm2 at patch position indicated). C. Macroscopic currents from a MscS-containing patch in response to an ultrasound step protocol (Vhold = 0 mV, transducer driving voltage = 0-0.3 V, Δ driving voltage = 50 mV, measured power in W/cm2 at patch position indicated).

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  Figure 4.. Ultrasound and pressure generate membrane tension to activate TRAAK channels. A. (left) Overlaid macroscopic currents and (right) corresponding fluorescent images from a TRAAK-containing patch in response to pressure (periwinkle) and ultrasound (green) stimulation. Traces and images are compared from the same patch activated to high (upper) and moderate (lower) I/Imax. Fits (red) and determined membrane radii are indicated on the images. Similar patch radii are observed when ultrasound or pressure stimuli generate similar channel activation. B. Normalized current-patch radius relationship calculated from a single patch in response to ultrasound and pressure stimulation. C. Comparison of patch radii observed during ultrasound or pressure stimulation that resulted in similar I/Imax values. Data from 5 different patches is shown (p = 0.18, paired t-test, not significant).