Fig. 2: Light-induced capacitance changes generate Icap.
From: Photolipid excitation triggers depolarizing optocapacitive currents and action potentials
a, b Time trace of PLB capacitance (black line; an average of 5 consecutively-recorded traces) indicating the 50 ms exposure intervals to blue light (blue background) and UV light (purple background). UV illumination immediately prior to blue light exposure at 1.15 s and blue light illumination immediately prior to UV light exposure at 11.17 s ensures a cis- and trans-enriched photostationary state, respectively. In a, the torus of the solvent-depleted PLB was small (image on the left). In b, C was recorded in the presence of a large solvent torus, as apparent in the corresponding PLB image on the right. Note the increased relaxation amplitude following blue light exposure relative to a. Scale bar is 25 µm in both images. c, d C changes exponentially as zoom-ins into the (c) blue (blue background) and (d) UV light (purple background) illumination intervals shown in a demonstrate. e, f The graphs below the recordings of C show Icap with (e) blue and (f) UV light exposure recorded at V = ± 110 mV (black lines; each averaged from 20 consecutively-recorded current traces). The overlaid red points are calculated from the respective above capacitance trace by numerical differentiation and subsequent multiplication with ±110 mV, as indicated by the arrows. g, h The graphs show Qcap obtained upon integration of Icap in Fig. 1c (g) and Fig. 1d (h) plotted over V; acc. Equation 8, the slope of a linear fit (black line) corresponds to ΔC upon photoisomerization (R² > 0.99). The green and blue circles correspond to the areas marked with the same color in e and f. i, j, Schematics of how photoisomerization from cis- to trans-OptoDArG generates tension within the membrane. The grey bars labeled PTFE symbolize the septum aperture within which the PLB is mounted, and green springs refer to the bilayer lipids other than OptoDArG. Upon blue light exposure, the area per photolipid decreases (atrans < acis) which, as the PLB is anchored laterally, causes stretching of the remaining lipids in the bilayer. The loading of the springs symbolizes tension within the PLB. The experimental data is from N = 7 independently prepared experiments, each comprising n > 10 technical replicates.
