Metabolic consequences of a reversed pH gradient in rat tumors

We have previously demonstrated (M. Stubbs, Z. M. Bhujwalla, G. M. Tozer, L. M. Rodrigues, R. J. Maxwell, R. Morgan, F. A. Howe, and J. R. Griffiths, NMR Biomed., 5: 351, 1992) that the intracellular pH (pHi) of several rat tumors is higher (> pH 7.0) than that of the tumor extracellular fluid (pHe), in contrast to normal tissues (e.g., liver) in which pHi is lower than pHe. In this paper we confirm a pHe of 6.8 +/- 0.07 (SEM) in Morris hepatoma 9618a by an independent method and report the tissue content of other ions by both 31P magnetic resonance spectroscopy and by conventional analysis in hepatomas and livers in rats. Compared with liver, tissue Na+ was 2-fold higher and tissue K+ was lower. Tissue Ca2+ was 8-fold higher (7.4 +/- 4.3 mumol/g wet weight) and tissue Pi was 2-fold higher (8.5 +/- 1.3 mumol/g wet weight) suggesting the presence of insoluble calcium phosphate. Cl- was unchanged (approximately 40 mumol/g wet weight), whereas HCO3- was lower in the hepatoma (12.4 +/- 0.83 compared to 15.5 +/- 0.76 mumol/g wet weight). Total tissue Mg2+ was similar in both tissues, but free [Mg2+] (calculated by two different methods) was approximately 5-fold lower in the hepatoma. The ATP values were 3.5-fold and [NAD]/[NADH] 9-fold lower in the hepatoma. The results are compatible with the hypothesis that the chronic partial hypoxia of tumor tissue involves changes in the linked equilibria of many ions and metabolites and may help explain such pathologies as calcification.