Changes in membrane potential of intact adipocytes measured with fluorescent dyes

The change in transmembrane potential of rat adipocytes was measured using the fluorescent probes 3,3′-diethylthiadicarbocyanine iodide, di-SC₂(5)], and 3,3′-dipropylthiadicarbocyanine iodide, di-SC₃(5)]. The fluorimetric technique was calibrated by altering the potassium ion concentration while keeping the sum of potassium and sodium ions at a constant concentration of 153 mM. A 3% change in relative fluorescence was equivalent to a membrane potential change of 1 mV. This method was used to measure changes in transmembrane potential by insulin and two insulin-mimetic agents: wheat germ agglutinin and ethanolamine.