Effect of phenylephrine on the compartmentation of inorganic phosphate in perfused rat liver during gluconeogenesis and urea synthesis: a 31P-n.m.r.-spectroscopic study
1994
Eriksson, O. | Pollesello, P. | Saris, N.E.L.
The transport of P(i) between the cytosol and the mitochondria was investigated in perfused rat liver stimulated with phenylephrine and metabolic precursors of glucose and urea: pyruvate, lactate, NH4(+) and ornithine. The relative concentrations of phosphorus metabolites in the liver were measured by (31)P-n.m.r. spectroscopy. When added simultaneously, phenylephrine and the precursors induced a decrease in the P(i) level which in 4-5 min reached a new steady state at 73% of the control level. After 5 min or more of stimulation the ATP level had also decreased. When the stimulation ended, P(i) and ATP returned to their initial levels within 15 min. In mitochondria isolated after 5 min of stimulation, P(i) was increased more than 2-fold as compared with control mitochondria and, in addition, an accumulation of P(i) from the perfusion buffer into the liver was observed. Phenylephrine by itself did not cause any significant changes in the ATP or P(i) levels, whereas the glucose and urea precursors in the absence of phenylephrine induced a 9% decrease in P(i), while ATP remained constant. The P(i) content of mitochondria isolated under these conditions was not significantly increased as compared with control mitochondria. These results showed that P(i) accumulated into the mitochondria by a mechanism possibly involving exchange for malate, and that a major part of the intramitochondrial P(i) was invisible by n.m.r.
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