Fig. 4

Glycolytic flux affected by intracellular [Na]_i and NKA function. a Schematic of the proposed mechanism of the effect of gramicidin-A on [Na⁺]_i and glycolysis. Gramicidin introduces an artificial Na⁺ leak, increasing [Na⁺]_i and glycolytic metabolism (Figure created using BioRender.com). b ²³Na TQF spectra showing the intracellular [Na⁺]_i peak relative to a reference capillary in MDA-MB-231 cells following membrane permeabilization with gramicidin and varying concentrations of titrated extracellular [Na⁺]_e. c Quantification of TQF ²³Na NMR spectra (proportional to [Na⁺]_i) following exposure to isotonic solutions of titrated [Na⁺]_e (n = 4), for 4T1 cells and MDA-MB-231 cells. d Quantification of glycolytic fluxes measured by the rate of [6,6-²H₂]d-glucose to [3,3-²H₂]l-lactate conversion at different concentrations of titrated [Na⁺]_i in murine 4T1 and human MDA-MB-231 breast cancer cells (n = 4). e Glycolytic fluxes in panel d replotted as a function of pump current derived from the analytical expression given by Silverman et al. [43] f Glycolytic flux measured at the highest concentration of 70 mM [Na⁺]_e following treatment with 1 µM ouabain treatment was not significantly altered in murine 4T1 cells but was significantly decreased in human MDA-MB-231 cells. ns p > 0.05, **** p < 0.0001. Data plotted as mean ± SD