Properties of cardiac I leak induced by photosensitizer-generated reactive oxygen

Abstract

We reported previously that photomodification of single frog cardiac cells by Rose Bengal induces a time-independent current, designated I leak, having a linear current-voltage (I/V) relationship. The purpose of the present study is to better characterize the properties of I leak. Initially, I leak has a reversal potential (E R) near −70 mV, but with time, E R shifts toward a final value near 0 mV. This shift in E R is accompanied by a marked increase in conductance (slope of I/V relationship). Evidence is presented that the depolarizing shift in E R with time during photomodification results from a loss of membrane selectivity allowing sodium to make an increasing contribution to I leak. Potassium also contributes to I leak, as indicated by marked depolarizing shifts in E R following replacement of intracellular potassium with either cesium or tetraethylammonium. Since these results occur in calcium-free external media, the depolarizing shifts in E R and conductance are not related to activation of a calcium-dependent nonselective cation channel. However, I leak does have some properties similar to nonselective cation currents recently reported to be activated by membrane breakdown products such as arachidonic acid and lysophosphoglycerides.