Difluorophosphate as a19F NMR probe of erythrocyte membrane potential

✍ Scribed by A. S. L. Xu; P. W. Kuchel

• Book ID: 104654285
• Publisher: Springer
• Year: 1991
• Tongue: English
• Weight: 770 KB
• Volume: 19
• Category: Article
• ISSN: 1432-1017
• DOI: 10.1007/bf00183323

✦ Synopsis

Erythrocyte membrane potential can be estimated by measuring the transmembrane concentration (activity) distribution of a membrane-permeable ion. We present here the study of difluorophosphate (DFP) as a 19F NMR probe of membrane potential. This bicarbonate and phosphate analogue has a pK, of 3.7_+ 0.2 (SD, n = 4) and therefore exists almost entirely as a monovalent anion at physiological pH. When it is incorporated into red cell suspensions, it gives two well resolved resonances that arise from the intra-and extracellular populations; the intracellular resonance is shifted ~ 130 Hz to higher frequency from that of the extracellular resonance. Hence the transmembrane distribution of DFP is readily assessed from a single 19F NMR spectrum and the membrane potential can be calculated using the Nernst equation. The membrane potential was independent of, DFP concentration in the range 4 to 59 raM, and haematocrit of the cell suspensions of 31.0 to 61.4%. The membrane potential determined by using DFP was 0.94-t-0.26 of that estimated from the transmembrane pH difference. The distribution ratios of intracellular/extracellular DFP were similar to those of the membrane potential probes, hypophosphite and trifluoroacetate. DFP was found to be transported across the membranes predominantly via the electrically-silent pathway mediated by capnophorin. Using magnetization transfer techniques, the membrane influx permeability-coefficient of cells suspended in physiological medium was determined to be 7.2-t-2.5 x 10 -6 cm s -1 (SD, n=4).