✦ LIBER ✦

The membrane potential of Ehrlich ascites tumor cells: An evaluation of the null point method

✍ Scribed by Thomas C. Smith; Susan C. Robinson

Publisher: John Wiley and Sons
Year: 1981
Tongue: English
Weight: 709 KB
Volume: 106
Category: Article
ISSN: 0021-9541
DOI: 10.1002/jcp.1041060309

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✦ Synopsis

The effects of valinomycin (25 pM) on the membrane potential and on initial, passive Na+ and K + movements have been determined in Ehrlich ascites tumor cells. The membrane potential of steady-state cells in a physiologic environment was -23.2 mV. Addition of valinomycin induced a small, significant hyperpolarization (V, = -29.6 mV) when averaged over the population tested. However, analyses of the response of individual cells to valinomycin showed two different potential effects: (1) the majority of cells hyperpolarized after treatment; but (2) a significant fraction depolarized when exposed to valinomycin. The V, of steady-state cells incubated in saline with K+ at concentrations of 21 mM or 75 mM was -21.4 mV and -22.0 mV, respectively. Addition of valinomycin to these cells was without effect on V,, thus establishing the "null point" responses. Only for cells incubated in saline with a K + of 75 mM was there agreement between V, and K + equilibrium potential (V,). Determinations of cellular Na+ and K+ showed that valinomycin induced net losses of K + and gains of Na+ by cells incubated in either physiologic saline or saline with a K+ concentration of 21 mM. However, the cellular K + of cells incubated in saline with a K + concentration of 75 mM was unaltered by valinomycin. There was a two-to threefold increase in K+ permeability of the cell membrane in the presence of valinomycin. These results are consistent with the existence of two null points in the membrane-potential response to valinomycin: One is established when the membrane potential corresponds to V,; the second occurs when the effects of valinomycin on K + loss from the cell are exactly offset by its inhibition of active Na+ + K + transport.

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