We reported previously that photomodification of single frog cardiac cells by Rose Bengal induces a time-independent current, designated Ileak, having a linear current-voltage (I/V) relationship. The purpose of the present study is to better characterize the properties of Ileak. Initially, Ileak has a reversal potential (ER) near -70 mV, but with time, ER shifts toward a final value near 0 mV. This shift in ER is accompanied by a marked increase in conductance (slope of I/V relationship). Evidence is presented that the depolarizing shift in ER with time during photomodification results from a loss of membrane selectivity allowing sodium to make an increasing contribution to Ileak. Potassium also contributes to Ileak, as indicated by marked depolarizing shifts in ER following replacement of intracellular potassium with either cesium or tetraethylammonium. Since these results occur in calcium-free external media, the depolarizing shifts in ER and conductance are not related to activation of a calcium-dependent nonselective cation channel. However, Ileak does have some properties similar to nonselective cation currents recently reported to be activated by membrane breakdown products such as arachidonic acid and lysophosphoglycerides.
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Acknowledgements -- The authors thank Joanne Tarr for her expert technical assistance and Kurt Kauffman for writing the computer programs for pulse generation and data acquisition. Supported by grants from American Heart Association (890714) and the National Institutes of Health, NHLBI (HL43008).
- Cardiac electrophysiology
- Free radicals
- Leak current
- Reactive oxygen