L-lactate transport in Ehrlich ascites-tumour cells

Abstract

Ehrlich ascites-tumour cells were investigated with regard to their stability to transport L-lactate by measuring either the distribution of [14C]lactate or concomitant H+ ion movements. The movement of lactate was dependent on the pH difference across the cell membrane and was electroneutral, as evidenced by an observed 1:1 antiport for OH- ions or 1:1 symport with H+ ions. 2. Kinetic experiments showed that lactate transport was saturable, with an apparent Km of approx. 4.68 mM and a Vmax. as high as 680 nmol/min per mg of protein at pH 6.2 and 37 degrees C. 3. Lactate transport exhibited a high temperature dependence (activation energy = 139 kJ/mol). 4. Lactate transport was inhibited competitively by (a) a variety of other substituted monocarboxylic acids (e.g. pyruvate, Ki = 6.3 mM), which were themselves transported, (b) the non-transportable analogues alpha-cyano-4-hydroxycinnamate (Ki = 0.5 mM), alpha-cyano-3-hydroxycinnamate (Ki = 2mM) and DL-p-hydroxyphenyl-lactate (Ki = 3.6 mM) and (c) the thiol-group reagent mersalyl (Ki = 125 muM). 5. Transport of simple monocarboxylic acids, including acetate and propionate, was insensitive to these inhibitors; they presumably cross the membrane by means of a different mechanism. 6. Experiments using saturating amounts of mersalyl as an "inhibitor stop" allowed measurements of the initial rates of net influx and of net efflux of [14C]lactate. Influx and efflux of lactate were judged to be symmetrical reactions in that they exhibited similar concentration dependence. 7. It is concluded that lactate transport in Ehrlich ascites-tumour cells is mediated by a carrier capable of transporting a number of other substituted monocarboxylic acids, but not unsubstituted short-chain aliphatic acids.

The effects of host carbogen (95% oxygen/5% carbon dioxide) breathing on metabolic characteristics of Morris hepatoma 9618a

“…Gullino (1976) observed a similar decrease in the pH of interstitial fluid in his model of implanted micropore chambers within tumour tissue when the animals breathed 10% carbon dioxide in air, so it is not unexpected. Protons and lactate-can move together on the monocarboxylate carrier and the distribution of H+ and lactate-across the plasma membrane tends to assume the relationship [H+][lactateJ / [H+1]e[lactate-]e = 1 (Spencer and Lehninger, 1976;Veech, 1991). These assumptions appear to hold reasonably well for tumours in the steady state (Stubbs et al, 1994).…”

Necrotic core in EMT6/Ro tumour spheroids: Is it caused by an ATP deficit?

“…In Ehrlich tumour cells the Michaelis-Menten constant, K m , of transport kinetics has been found to be 20 mM at 37 o C and pH 7.2 (Spencer and Lehninger, 1976) and, with a different technique, 5.34 mM in the same conditions (Carpenter and Halestrap, 1994). In the mammary carcinoma MDA-MB231, high affinity (MCT2) and low affinity (MCT4) transporters have been evidenced (Wang and Morris, 2007), with a prevalent flux through MCT4 (K m = 21.3 mM).…”

The relationship between extracellular lactate and tumour pH in a murine tumour model of ischaemia-reperfusion

“…Many tumours use glycolysis to maintain their energy status, and a specific monocarboxylate carrier, through which lactic acid can be effluxed from the cell, has been identified in Ehrlich ascites tumour cells (lactic acid is fully dissociated at physiological pH to lactate ions) (Spencer and Lehninger, 1976). Homeostasis of cellular pHi is also maintained by efflux of H+ by the Na+/H+ antiport exchanger, which has been shown to be ubiquitous in mammalian cells and is necessary for the growth of some tumours Rotin et al, 1989).…”

“…The high rate of lactate production by tumour cells, combined with the poor vascular structure in tumours, results in a significantly acidic extracellular space, which has been investigated using different techniques (Vaupel et al, 1989;Griffiths, 1991;Gillies et al, 1994). In addition, because H+ and lactate move together on the monocarboxylate carrier, the distribution of H+ and lactate tend to assume a reciprocal relationship with pH across the plasma membrane (Spencer and Lehninger, 1976;Veech, 1991;Stubbs et al, 1994). Clamp duration (h) We have shown previously that extracellular pH (pHe) is acidic in the CaNT murine tumour (using inserted pH microelectrodes or non-invasive magnetic resonance spectroscopy) with intracellular pH (pHi) maintained close to neutrality (Stubbs et al, 1992;McCoy et al, 1995).…”