Determination of the membrane potential of cultured mammalian Schwann cells and its sensitivity to potassium using a thiocarbocyanine fluorescent dye.

The membrane potential of cultured rat sciatic nerve Schwann cells was determined with conventional microelectrode and voltage-sensitive fluorescent dye, Di-S-C3(5), optical techniques. The value for membrane potential obtained with microelectrodes was -42.1 +/- 4.7 mV (n = 8). Using optically determined fluorescent intensity changes caused by changes in external potassium ion concentration, in the presence or absence of valinomycin (null point method), the membrane potential was estimated at -45.7 +/- 6.2 mV (n = 7); with a gramicidin and valinomycin double ionophore method it was -52.2 +/- 9.1 (n = 4). The membrane potential of Schwann cells was found to be potassium sensitive at and above the physiological range of [K+] at 27.5 mV/10x delta[K+], which is approximately half the Nernstian value. This result suggests that other ion permeabilities strongly influence the resting membrane potential of cultured Schwann cells. Since Na+ had little effect on the membrane potential, it is concluded that Cl- is a likely candidate for the other permeant ionic species. The optical method has been shown to be a useful tool for the systematic study of the membrane potential of Schwann cells in culture and for the characterization of its ionic basis and regulation.