Membrane potential can influence the rate of membrane photomodification

Though cellular photomodification has been shown to change cellular resting membrane potential, an effect of membrane potential on the rate of photomodification has never been reported. Here we demonstrate that the rate of photomodification of potassium channels in frog atrial cells is voltage dependent. The rate of potassium channel photomodification using negatively charged Rose Bengal as the photosensitizer is about 2.5 times greater at the resting membrane potential of -70 mV compared to +40 mV. Similar results are obtained using the positively charged photosensitizer methylene blue. On the other hand, the rate of photomodified increase of leak current in the same cells does not significantly change in this voltage range with Rose Bengal as photosensitizer, but demonstrates a voltage dependence like that of potassium current when methylene blue is the photosensitizer. These observations cannot be explained based on voltage-dependent partitioning of the sensitizer, as similar effects on potassium current were obtained using either a positively charged or negatively charged sensitizer.