Quantitation of corneal endothelial potentials using a carbocyanine dye

The carbocyanine dye, diS-C3-(5) was used to quantitate the plasma membrane potential of the bullfrog corneal endothelium. It was shown that valinomycin hyperpolarized the endothelial cell and that in the presence of the ionophore the membrane potential largely reflected the K+ equilibrium potential. Using calibration curves constructed by changing medium K+ concentration in the presence of valinomycin, and nigericin and ouabain to abolish ion gradients and electrogenic pump activity, the cell membrane potential was calculated to be 28.6 +/- 4.2 mV. The major source of this potential was a K+ diffusion potential, and the membrane Na+ conductance reduced the cell potential to less than the apparent K+ equilibrium potential of 51.5 +/- 5.1 mV. About 20% of the cell potential could be ascribed to the rheogenic (Na+ + K+)-ATPase.