Radiolytic and photodynamic modifications of ion transport through the plasma membrane of OK cells: a comparison

Purpose: This study seeks to compare functional modifications of the plasma membrane induced either by water radiolysis (80 kV X-rays) or by visible l ight in the presence of the photosensitizer photofrin II. The two methods g enerate different kinds of free radicals and other reactive species such as singlet oxygen. Their effect on the electrical properties of the plasma me mbrane is investigated. Method: The patch-clamp technique (whole-cell and inside-out configuration) was applied to the plasma membrane of an epithelial cell line (opossum kid ney (OK) cells). Results: Generation of the reactive species gave rise to a decay of the mem brane potential, to an inactivation of K+-channels, and to an increase of t he leak conductance of the membrane. AU three effects were strongly involve d in photomodification of the membrane. Following X-ray exposure (doses up to 1000 Gy) on the other hand, the decay of the membrane conductance caused by inactivation of ion channels was predominant, while the increase of the leak conductance and the depolarization were comparatively minor responses . Conclusion: Photomodification of the plasma membrane by visible light in th e presence of the membrane-active sensitizer photofrin II is of considerabl y greater consequence for the electrical properties of the membrane, compar ed with exposure to ionizing radiation of the membrane and its aqueous envi ronment. The differences are thought to reflect the types of reactive speci es produced by the two methods and their site of generation.