Ratiometric measurement of endothelial depolarization in arterioles with a potential-sensitive dye

A fluorescence ratio technique based on the voltage-sensitive dye 1-(3-sulfonatopropyl)-8-[beta-[2-(di-n-butylamino)-6-naphthyl]vinyl] pyridinium betaine (di-8-ANEPPS) has been developed for recording membrane potential changes during vascular responses of arterioles. Perfusion of hamster cheek pouch arterioles with the dye labeled the endothelial cell layer. Voltage responses from the endothelium of intact arterioles were determined by analysis of voltage-induced shifts in fluorescence emission wavelengths from dye spectra imaged from the vessel wall. Membrane depolarization caused the dye spectrum to shift toward blue wavelengths, with maximal fluorescence changes near 560 and 620 nm. In isolated nonperfused arterioles, comparison of continuous dual-wavelength recordings with simultaneous microelectrode recordings showed that the ratio of fluorescence intensities (fluorescence at 620 nm to fluorescence at 560 nm) accurately followed changes in membrane potential (6-21 mV) during vasoconstriction. The dye response was linear with respect to potential changes from -56 to -6 mV, with a voltage sensitivity of 9.7% change in the ratio per 100 mV. Membrane potential responses from in vitro and in vivo arterioles after potassium stimulation consisted of rapid (<0.5 -s) depolarization followed by slow repolarization over several seconds. Potassium-induced depolarizations were conducted along arterioles, and the values of the electrical length constant for conducted depolarization determined by optical and microelectrode methods were in agreement. We conclude that ratio analysis of di-8-ANEPPS fluorescence emission can be used to accurately record membrane potential changes on the time scale of seconds during vasomotor activity from arterioles.