3,3′-Dipropylthiadicarbocyanine (diSC₃(5)) is a fluorescent dye that has been used to monitor cell membrane potential.^1,2,3It displays excitation/emission maxima of 622/670 nm, respectively, and, upon cell hyperpolarization, it enters cells, and exhibits a shift in emission maxima to 688 nm and a decrease in fluorescence intensity.¹When the cell membrane is depolarized, the fluorescence intensity of diSC₃(5) increases as it exits the cells. However, diSC₃(5) (3 µM) also induces membrane hyperpolarization, increases intracellular sodium levels, and decreases intracellular potassium levels in Ehrlich ascites tumor cells, as well as increases potassium membrane permeability by 64.6% in Ehrlich ascites tumor cells in the presence of the Na⁺/K⁺-ATPase inhibitor ouabain.²It also reduces cellular ATP levels in the absence of glucose and induces acid production and inhibits oxygen consumption in the presence of glucose in Ehrlich ascites tumor cells when used at a concentration of 3 µM.³

1.Sims, P.J., Waggoner, A.S., Wang, C.H., et al.Studies on the mechanism by which cyanine dyes measure membrane potential in red blood cells and phosphatidylcholine vesiclesBiochemistry13(16)3315-3330(1974) 2.Smith, T.C., and Robinson, S.C.The effect of the fluorescent probe, 3,3’-dipropylthiodicarbocyanine iodide, on the membrane potential of Ehrlich ascites tumor cellsBiochem. Biophys. Res. Commun.95(2)722-727(1980) 3.Smith, T.C., Herlihy, J.T., and Robinson, S.C.The effect of the fluorescent probe, 3,3’-dipropylthiadicarbocyanine iodide, on the energy metabolism of Ehrlich ascites tumor cellsJ. Biol. Chem.256(3)1108-1110(1981)