Photodynamic membrane damage at the level of single ion channels

Illumination of cellular membranes by visible light in the presence of appropriate photosensitizers is known to inactivate specific ionic pathways and to increase the unspecific leak conductance of the membranes. While previous studies have concentrated on the macroscopic ionic currents, the present study separates the two phenomena at the microscopic level. Using opossum kidney (OK) cells as epithelial model system and photofrin II as sensitizer, the patch-clamp technique in inside-out configuration has been applied to show the inactivation of single ion channels immediately after start of illumination and the subsequent strong increase of the leak conductance. Inactivation is shown for two kinds of channels: the large-conductance Ca2+-dependent K+ channel (maxi-K(Ca)) and the stretch-activated nonselective cation channel (SA-cat).