Inorganic pyrophosphate is located primarily in the mitochondria of the hepatocyte and increases in parallel with the decrease in light-scattering induced by gluconeogenic hormones, butyrate and ionophore A23187.
1. The effects of a variety of hormones on the PPi content and light-scattering of isolated rat liver cells was studied. 2. The basal PPi content was about 130 pmol/mg of cell protein, and increased after hormone addition, in parallel with a decrease in light-scattering which we have observed previously [Quinlan, Thomas, Armston & Halestrap (1983) Biochem. J. 214, 395-404]. 3. The mean increases in PPi content with the agonists shown (as pmol/mg of protein) were: 0.1 microM-glucagon, 25; 20 microM-phenylephrine, 30; 25 nM-vasopressin, 127; glucagon + phenylephrine, 115; glucagon + vasopressin, 382; 100 microM-ADP, 50; 15 microM-A23187, 72; 1 mM-butyrate, 80. 4. In the absence of extracellular Ca2+, vasopressin had little effect on either the PPi content or the light-scattering of hepatocytes. 5. The magnitude of the increase in PPi content correlated with that of the decrease in light-scattering irrespective of the stimulating agent, provided that the PPi did not exceed 300 pmol/mg of protein. Above this value little additional change in light-scattering was observed. 6. Subcellular fractionation showed that over 90% of the cellular PPi was intramitochondrial in both control and stimulated cells. 7. The data support the conclusions of previous experiments using isolated liver mitochondria [Davidson & Halestrap (1987) Biochem. J. 246, 715-723] that hormones increase the mitochondrial matrix volume through a Ca2+-induced rise in matrix [PPi]. 8. It is further proposed that this increase in mitochondrial [PPi] allows entry of ADP into the mitochondria in exchange for PPi and is therefore responsible for the increase in total mitochondrial adenine nucleotides observed after hormone treatment.
Davidson
A M
AM
Department of Biochemistry, School of Medical Sciences, University of Bristol, U.K.
Halestrap
A P
AP
D000818:Animals; D002087:Butyrates / Q000494:pharmacology*; D020148:Butyric Acid; D000001:Calcimycin / Q000494:pharmacology*; D002118:Calcium / Q000494:pharmacology; D011756:Diphosphates / Q000378:metabolism*; D006728:Hormones / Q000494:pharmacology*; D007424:Intracellular Fluid / Q000187:drug effects / Q000378:metabolism; D008027:Light; D008297:Male; D008930:Mitochondria, Liver / Q000187:drug effects / Q000378:metabolism*; D010656:Phenylephrine / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D012542:Scattering, Radiation; D014667:Vasopressins / Q000494:pharmacology
D002087:Butyrates; D011756:Diphosphates; D006728:Hormones; D020148:Butyric Acid; D014667:Vasopressins; D010656:Phenylephrine; D000001:Calcimycin; D002118:Calcium