Cation permeability and ouabain-insensitive cation flux in the Ehrlich ascites tumor cell

Abstract

The components of Na and K flux across the plasma membrane have been investigated in the Ehrlich ascites tumor cell. At intracellular K levels of approximately 100 mM, unidirectional K influx is composed of a ouabain-sensitive component, a ouabain-insensitive, nondiffusional component and a diffusional component. Unidirectional K efflux is composed of an external K-dependent component and a diffusional component. Upon reduction of intracellular K to approximately 50 mM, the external K-dependent component becomes maximal and diminishes upon further reduction of intracellular K. Unidirectional Na efflux is composed of a ouabain-sensitive component, a diffusional component and a saturable, external Na-dependent, ouabain-insensitive component. Unidirectional Na influx may be accounted for by a diffusional component, based on estimates of membrane permeability to Na, membrane potential and Na distribution. This would suggest that the ouabain-insensitive, external Na-dependent Na efflux is not Na--Na exchange. The origin of the cell membrane potential has not been previously established in the Ehrlich ascites cell. From the diffusional components of Na and K flux determined in these experiments, the membrane permeabilities to Na and K have been estimated. These permeabilities, in conjunction with the Na and K distributions across the plasma membrane, predict a cell membrane potential of - 18mV (inside negative). Passive Cl distributions in these cells predict a cell membrane potential of - 21 mV, which is in agreement with previous microelectrode measurements and dibenzyldimethylammonium distributions. The results are therefore consistent with the conclusion that the magnitude and polarity of the cell membrane potential in the Ehrlich ascites cell is dictated primarily by Na and K.

Reduction of K+ efflux in cultured mouse fibroblasts, by mutation or by diuretics, permits growth in K+-deficient medium.

“…One of the mutants, LTK-5, exhibited altered activity of a Na+-K+ cotransport system (12, 13) similar to that described in human (14,15) and avian (16) erythrocytes and in Ehrlich cells (17)(18)(19)(20)(21) and murine fibroblasts (22,23). Specifically, in characterizing the mutant relative to its parent strain under conditions of K+ depletion and high external K+, Gargus and Slayman (13) noted that LTK-5 demonstrated enhanced furosemidesensitive, Na+-dependent K+ influx.…”

K+ influx components in ascites cells: The effects of agents interacting with the (Na++K+)-pump

“…In Ehrlich cells, the ouabain-sensitive component has been characterized as a net flux, mediated by the (Na § +K +)-pump; the furosemide-sensitive component (equivalent to the C1 -dependent flux: [1] and this paper) as exchange diffusion; and the residual flux as passive diffusion [18,23]. In first approximation this same flux characterization also holds for our strain of ascites cells; in fact, we have previously applied it [1].…”

“…(5-20 nCi/mi) at zero time: this isotope has been shown [18] to act as a tracer for K + in Ehrlich ceils. At fixed intervals, varying between 4 and 8 rain over a total of 24-40 rain, uptake was terminated on a total of 4 to 6 duplicate 4-ml samples of cell suspension by centrifuging at 1,500 rpm for 1 rain.…”

⁸⁷Rb, ²³Na and ³¹P Nuclear Magnetic Resonance Spectroscopy of the Perfused Rat Kidney

“…Experiments in a number of biological sys tems have shown that Rb+ and K+ are very similarly transported by Na+-K+-ATPase [20,21]. Using equation (3) to calculate the net K+ influx from the measured 87Rb+ flux into kid ney gives an initial inward K ' flux of 9.1 pmol/ g/min in the intact isolated perfused rat kidney.…”