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

Abstract

Purpose:This study seeks to compare functional modifications of the plasma membrane induced either by water radiolysis (80kV X-rays) or by visible light in the presence of the photosensitizer photofrin II. The two methods generate different kinds of free radicals and other reactive species such as singlet oxygen. Their effect on the electrical properties of the plasma membrane 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 kidney (OK) cells). Results: Generation of the reactive species gave rise to a decay of the membrane potential, to an inactivation of K-channels, and to an increase of the leak conductance of the membrane. All three effects were strongly involved in photomodification of the membrane. Following X-ray exposure (doses up to 1000Gy) 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 the presence of the membrane-active sensitizer photofrin II is of considerably greater consequence for the electrical properties of the membrane, compared with exposure to ionizing radiation of the membrane and its aqueous environment. The differences are thought to reflect the types of reactive species produced by the two methods and their site of generation.