Figure 3.

Absorbance and action spectra of MAL-AZO-QA. (a) The ultraviolet and visible light spectrum of a MAL-AZO-QA-glutathione adduct (10 μM) in oocyte bath solution. To maximize the trans and cis isomers, the solution was exposed to visible and ultraviolet light, respectively, for 3 min. To generate the adduct, MAL-AZO-QA (1 M) was treated with reduced glutathione (1.5 M) for 12 h at 21 °C. (b) Unblocking of Shaker channels at different wavelengths. Currents are from an inside-out patch alternately exposed to various wavelengths between 300 and 480 nm to unblock the channels, and to 500 nm light to reblock the channels. (c) Reblocking of Shaker channels at different wavelengths. The time course of blocking at various wavelengths of visible light. Each trial is preceded by 1-min irradiation at 380 nm to unblock the channels. Traces are superimposed for comparison. Normalized current amplitudes were measured at 0.2 min after onset of blocking. (d) Action spectra for unblocking (left curve) and blocking (right curve) of Shaker K⁺ channels. Unblock (left axis): Current unblocked at each wavelength divided by current at 380 nm (n = 3–8 patches per wavelength). Currents were compared within each patch. Block (right axis): Fraction of normalized current blocked at 0.2 min after illumination with visible light (n = 2–7 patches per wavelength).