Photosensitizer Binding to Lipid Bilayers as a Precondition for the Photoinactivation of Membrane Channels

Abstract

The photodynamic activity of sulfonated aluminum phthalocyanines (AlPcS(n), 1 </= n </= 4) was found to correlate with their affinity for membrane lipids. Adsorbing to the surface of large unilamellar vesicles (LUVs), aluminum phthalocyanine disulfonate induced the highest changes in their electrophoretic mobility. AlPcS(2) was also most efficient in mediating photoinactivation of gramicidin channels, as revealed by measurements of the electric current across planar lipid bilayers. The increase in the degree of sulfonation of phthalocyanine progressively reduced its affinity for the lipid bilayer as well as its potency of sensitizing gramicidin channel photoinactivation. The portion of photoinactivated gramicidin channels, alpha, increased with rising photosensitizer concentration up to some optimum. The concentration at which alpha was at half-maximum amounted to 80 nM, 30 nM, 200 nM, and 2 microM for AlPcS(1), AlPcS(2), AlPcS(3), and AlPcS(4), respectively. At high concentrations alpha was found to decrease, which was attributed to quenching of reactive oxygen species and self-quenching of the photosensitizer triplet state by its ground state. Fluoride anions were observed to inhibit both AlPcS(n) (2 </= n </= 4) binding to LUVs and sensitized photoinactivation of gramicidin channels. It is concluded that photosensitizer binding to membrane lipids is a prerequisite for the photodynamic inactivation of gramicidin channels.

Excitation of fluorescent dyes inactivates the outer hair cell integral membrane motor protein prestin and betrays its lateral mobility

“…E A Deiters' cell treated with di-8-ANEPPS showed no reduction of linear capacitance during exposure capacitance or conductance is not likely to be due to diffusion of reactive species far from areas of exposure, since inactivation stops immediately after the light is turned off. This is expected since photo-sensitizers probably act after binding to the membrane, and the estimated lifetime and diffusion of the evolved reactive species, e.g., singlet oxygen, are of the order of a few microseconds, and a hundred nanometers, respectively (see [19] for discussion and references). Thus, the fiber optic exposures that we made probably resulted in highly restricted lesions.…”

(Coumarin‐4‐yl)methyl Esters as Highly Efficient, Ultrafast Phototriggers for Protons and Their Application to Acidifying Membrane Surfaces

“…The charge brought by adsorption of 3 to diphytanoyl-phosphatidylcholine (DPhPC) vesicles was monitored and used to calculate the electrical potential (z) at the shear plane of the vesicles. [24,25] With increasing concentrations of 3, the zpotential saturated at À20 mV (in 20 mm NaCl), indicating that the binding site for one molecule of 3 is at least 20 lipid molecules in size.…”

(Cumarin‐4‐yl)methylester als hocheffiziente und ultraschnelle Phototrigger für Protonen und ihre Anwendung zur Oberflächenansäuerung von Membranen

“…Die durch die Adsorption von 3 hervorgerufene negative Aufladung der ansonsten neutralen Diphytanoylphosphatidylcholin(DPhPC)-Vesikel wurde elektrophoretisch verfolgt und zur Berechnung des elektrischen Potentials (z) an der Scherebene der Vesikel herangezogen. [24,25] Mit zunehmender Konzentration von 3 näherte sich das z-Potential asymptotisch an À20 mV an (in 20 mm NaCl). Demnach umfasst die Bindungsstelle für ein Molekül 3 mindestens 20 Lipidmoleküle.…”