COMPARTMENTATION OF INORGANIC-PHOSPHATE IN PERFUSED-RAT-LIVER - CAN CYTOSOL BE DISTINGUISHED FROM MITOCHONDRIA BY P-31 NMR

Compartmentation of inorganic phosphate was studied in intact perfused rat liver at 4-degrees-C by P-31 NMR. It was shown that in cytosolic pH or cytosolic P(i) concentration induced the appearance of an additi onal P(i) resonance at low field which was assigned to P(i) from an al kaline compartment. Valinomycin (K+ ionophore) induced a further split ting of the lines whereas nigericin (K+/H+ antiport) or potassium cyan ide (inhibitor of cytochrome oxidase) had opposite effects. As valinom ycin acts mainly on the cytosolic/mitochondrial K+ gradient and KCN on the mitochondrial respiratory chain, it was deduced that the alkaline compartment as revealed by the second P(i) resonance was probably mit ochondria. Single P(i) lines observed on perchloric extracts of livers exhibiting two resonances during cold perfusion confirmed that the sp lit peaks in the intact liver indeed arose from the same molecular spe cies.