EFFECTS OF HEAVY-WATER ON HEPATIC INTRACELLULAR PH AND PHOSPHATIDYLCHOLINE TURNOVER - A P-31 NMR-STUDY

The short term effects of heavy water ((H2O)-H-2) on intracellular pH (pH(i)) and phosphatidylcholine (PtdCho) turnover have been studied by P-31 NMR spectroscopy in the perfused mouse liver metabolizing alanin e. Hepatic pH(i) decreased from 7.19 +/- 0.01 (n = 10) to 7.01 +/- 0.0 3 (n = 4) after the addition of 6 mM alanine to Krebs Ringer bicarbona te (KRB) perfusion medium. Replacement of 50% of the KRB water with (H 2O)-H-2 during alanine perfusion inhibited the intracellular acidifica tion induced by alanine and caused: i) a decrease in the hepatic conte nt of PtdCho, and ii) increases in phosphocholine and glycerophosphoch oline, respectively Amiloride (1 mM) or 5-(N-ethyl-N-isopropyl)-amilor ide (10 mu M), two previously reported inhibitors of the Na+/H+ exchan gers, mimicked the effects produced by (H2O)-H-2 on pH(i) and PtdCho t urnover. Replacement of 50% of the KRB water with (H2O)-H-2 or the add ition of 1 mM amiloride to KRB only, did not modify pH(i) nor increase the levels of phosphocholine or glycerophosphocholine. Thus, the obse rved increases are the result of alanine perfusion in the presence of (H2O)-H-2 or amiloride. These results suggest that (H2O)-H-2 behaves s imilarly to previously reported inhibitors of Na+/H+ exchange, disclos ing also a novel role for PtdCho metabolism in the regulation on hepat ic pH(i).