³¹P nuclear magnetic resonance studies of isolated rat liver cells

Abstract

PHOSPHOROUS nuclear magnetic resonance (NMR) has recently been used in studies of intact cells, and many phosphate metabolites have been observed and identified. One valuable result of these studies has been the determination of intracellular pH (refs 1–3) using the fact that the position of the ³¹P NMR peak of inorganic phosphate (P_i) shifts as P_i is protonated. ³¹P NMR measurements of energised Escherichia coli³ have shown that a δpH is maintained across the membranes in agreement with previous measurements of δpH determined from the distribution of a weak acid, such as DMO, between the inner and outer volumes⁴. Although there is considerable evidence for the existence of δpH from studies of isolated mitochondria^5–8, no direct measurements have been reported of a pH difference between cytosol and mitochondria in whole cells in vivo. However, there is indirect evidence for such a gradient from studies of the distribution of anions between the cytoplasmic and mitochondrial contents of disrupted rat liver cells⁹. In this preliminary report we show that ³¹P NMR can be used to detect phosphate metabolites in rat liver cells and to measure directly δpH between mitochondria and cytosol in the intact cell.