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

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Abstract
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/10 × Δ[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.