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Elliott J, Geddes RF. New concepts in phosphorus homeostasis and its impact on renal health with particular reference to the cat. Vet J 2022; 283-284:105842. [PMID: 35577278 DOI: 10.1016/j.tvjl.2022.105842] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2021] [Revised: 05/08/2022] [Accepted: 05/10/2022] [Indexed: 11/17/2022]
Abstract
New discoveries relating to phosphorus homeostasis include the hormones fibroblast growth factor-23 and klotho produced by bone and kidney. These hormones, together with novel understanding of how calcium and phosphate ions are carried in colloidal form as calciprotein particles, have changed our view of how phosphorus is regulated. Recognition that high dietary intake of inorganic forms of phosphorus in humans is a risk factor for both cardiovascular and renal diseases have led to re-examination of the impact of inorganic sources of phosphorus in prepared cat foods on renal health. Data suggest that when homeostatic mechanisms lead to proximal tubular (S3 segment) phosphate concentrations exceeding 3.25mmol/L for a significant part of the day, tubular stress and structural kidney damage ensues. Recent experimental rodent studies support the concept that calciprotein particles form in the proximal tubule at these prevailing phosphate concentrations and trigger proximal tubular damage. Long-term feeding studies in cats suggest that carefully formulated prepared diets containing 1g/Mcal of inorganic phosphorus (in the form of sodium tripolyphosphate or potassium monophosphate and pyrophosphate), resulting in estimated tubular phosphate concentrations <2.5mmol/L can be fed to healthy adult cats without detectable adverse effects on renal health.
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Affiliation(s)
- Jonathan Elliott
- Department of Comparative Biomedical Sciences, Royal Veterinary College, Royal College Street, London NW1 0TU, UK.
| | - Rebecca F Geddes
- Department of Clinical Science and Services, Royal Veterinary College, Hawkshead Lane, Hatfield, Hertfordshire AL9 7TA, UK
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Bódis K, Knebel B, Nowotny B, Bobrov P, Kupriyanova Y, Zaharia OP, Karusheva Y, Schön M, Wolkersdorfer M, Burkart V, Al-Hasani H, Markgraf D, Müssig K, Roden M, Szendroedi J. Hepatic energy metabolism in a family with a glucokinase gene mutation and dysglycemia. Diabetes Res Clin Pract 2022; 185:109779. [PMID: 35176401 DOI: 10.1016/j.diabres.2022.109779] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/29/2021] [Accepted: 02/09/2022] [Indexed: 11/29/2022]
Abstract
Carriers heterozygous for the D124N (c.370, GAC > AAC in exon 4) variant of GCK not only exhibit reduced insulin-secretion, but also impaired adipose insulin sensitivity, which may shift fatty acids towards the liver. This could contribute to increased hepatic lipid-accumulation and alterations of liver energy metabolism resulting in dysglycemia. ClinicalTrial.gov registration no: NCT01055093.
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Affiliation(s)
- Kálmán Bódis
- Department of Endocrinology and Diabetology, Medical Faculty and University Hospital, Heinrich Heine University Düsseldorf, Düsseldorf, Germany; Institute for Clinical Diabetology, German Diabetes Center, Leibniz Center for Diabetes Research at Heinrich Heine University, Düsseldorf, Germany; German Center for Diabetes Research, Partner Düsseldorf, München-Neuherberg, Germany
| | - Birgit Knebel
- German Center for Diabetes Research, Partner Düsseldorf, München-Neuherberg, Germany; Institute for Clinical Biochemistry and Pathobiochemistry, German Diabetes Center, Leibniz Center for Diabetes Research at Heinrich Heine University, Düsseldorf, Germany
| | - Bettina Nowotny
- Institute for Clinical Diabetology, German Diabetes Center, Leibniz Center for Diabetes Research at Heinrich Heine University, Düsseldorf, Germany; German Center for Diabetes Research, Partner Düsseldorf, München-Neuherberg, Germany
| | - Pavel Bobrov
- German Center for Diabetes Research, Partner Düsseldorf, München-Neuherberg, Germany; Institute for Biometrics and Epidemiology, German Diabetes Center, Leibniz Center for Diabetes Research at Heinrich Heine University, Düsseldorf, Germany
| | - Yuliya Kupriyanova
- Institute for Clinical Diabetology, German Diabetes Center, Leibniz Center for Diabetes Research at Heinrich Heine University, Düsseldorf, Germany; German Center for Diabetes Research, Partner Düsseldorf, München-Neuherberg, Germany
| | - Oana-Patricia Zaharia
- Institute for Clinical Diabetology, German Diabetes Center, Leibniz Center for Diabetes Research at Heinrich Heine University, Düsseldorf, Germany; German Center for Diabetes Research, Partner Düsseldorf, München-Neuherberg, Germany
| | - Yanislava Karusheva
- Institute for Clinical Diabetology, German Diabetes Center, Leibniz Center for Diabetes Research at Heinrich Heine University, Düsseldorf, Germany; German Center for Diabetes Research, Partner Düsseldorf, München-Neuherberg, Germany
| | - Martin Schön
- Institute for Clinical Diabetology, German Diabetes Center, Leibniz Center for Diabetes Research at Heinrich Heine University, Düsseldorf, Germany; German Center for Diabetes Research, Partner Düsseldorf, München-Neuherberg, Germany
| | | | - Volker Burkart
- Institute for Clinical Diabetology, German Diabetes Center, Leibniz Center for Diabetes Research at Heinrich Heine University, Düsseldorf, Germany; German Center for Diabetes Research, Partner Düsseldorf, München-Neuherberg, Germany
| | - Hadi Al-Hasani
- German Center for Diabetes Research, Partner Düsseldorf, München-Neuherberg, Germany; Institute for Clinical Biochemistry and Pathobiochemistry, German Diabetes Center, Leibniz Center for Diabetes Research at Heinrich Heine University, Düsseldorf, Germany
| | - Daniel Markgraf
- Institute for Clinical Diabetology, German Diabetes Center, Leibniz Center for Diabetes Research at Heinrich Heine University, Düsseldorf, Germany; German Center for Diabetes Research, Partner Düsseldorf, München-Neuherberg, Germany
| | - Karsten Müssig
- Department of Endocrinology and Diabetology, Medical Faculty and University Hospital, Heinrich Heine University Düsseldorf, Düsseldorf, Germany; Institute for Clinical Diabetology, German Diabetes Center, Leibniz Center for Diabetes Research at Heinrich Heine University, Düsseldorf, Germany; German Center for Diabetes Research, Partner Düsseldorf, München-Neuherberg, Germany
| | - Michael Roden
- Department of Endocrinology and Diabetology, Medical Faculty and University Hospital, Heinrich Heine University Düsseldorf, Düsseldorf, Germany; Institute for Clinical Diabetology, German Diabetes Center, Leibniz Center for Diabetes Research at Heinrich Heine University, Düsseldorf, Germany; German Center for Diabetes Research, Partner Düsseldorf, München-Neuherberg, Germany.
| | - Julia Szendroedi
- Department of Endocrinology and Diabetology, Medical Faculty and University Hospital, Heinrich Heine University Düsseldorf, Düsseldorf, Germany; Institute for Clinical Diabetology, German Diabetes Center, Leibniz Center for Diabetes Research at Heinrich Heine University, Düsseldorf, Germany; German Center for Diabetes Research, Partner Düsseldorf, München-Neuherberg, Germany
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Fritsch M, Koliaki C, Livingstone R, Phielix E, Bierwagen A, Meisinger M, Jelenik T, Strassburger K, Zimmermann S, Brockmann K, Wolff C, Hwang JH, Szendroedi J, Roden M. Time course of postprandial hepatic phosphorus metabolites in lean, obese, and type 2 diabetes patients. Am J Clin Nutr 2015; 102:1051-8. [PMID: 26423389 DOI: 10.3945/ajcn.115.107599] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2015] [Accepted: 08/26/2015] [Indexed: 01/06/2023] Open
Abstract
BACKGROUND Impaired energy metabolism is a possible mechanism that contributes to insulin resistance and ectopic fat storage. OBJECTIVE We examined whether meal ingestion differently affects hepatic phosphorus metabolites in insulin-sensitive and insulin-resistant humans. DESIGN Young, lean, insulin-sensitive humans (CONs) [mean ± SD body mass index (BMI; in kg/m(2)): 23.2 ± 1.5]; insulin-resistant, glucose-tolerant, obese humans (OBEs) (BMI: 34.3 ± 1.7); and type 2 diabetes patients (T2Ds) (BMI: 32.0 ± 2.4) were studied (n = 10/group). T2Ds (61 ± 7 y old) were older (P < 0.001) than were OBEs (31 ± 7 y old) and CONs (28 ± 3 y old). We quantified hepatic γATP, inorganic phosphate (Pi), and the fat content [hepatocellular lipids (HCLs)] with the use of (31)P/(1)H magnetic resonance spectroscopy before and at 160 and 240 min after a high-caloric mixed meal. In a subset of volunteers, we measured the skeletal muscle oxidative capacity with the use of high-resolution respirometry. Whole-body insulin sensitivity (M value) was assessed with the use of hyperinsulinemic-euglycemic clamps. RESULTS OBEs and T2Ds were similarly insulin resistant (M value: 3.5 ± 1.4 and 1.9 ± 2.5 mg · kg(-1) · min(-1), respectively; P = 0.9) and had 12-fold (P = 0.01) and 17-fold (P = 0.002) higher HCLs, respectively, than those of lean persons. Despite comparable fasting hepatic γATP concentrations, the maximum postprandial increase of γATP was 6-fold higher in OBEs (0.7 ± 0.2 mmol/L; P = 0.03) but only tended to be higher in T2Ds (0.6 ± 0.2 mmol/L; P = 0.09) than in CONs (0.1 ± 0.1 mmol/L). However, in the fasted state, muscle complex I activity was 53% lower (P = 0.01) in T2Ds but not in OBEs (P = 0.15) than in CONs. CONCLUSIONS Young, obese, nondiabetic humans exhibit augmented postprandial hepatic energy metabolism, whereas elderly T2Ds have impaired fasting muscle energy metabolism. These findings support the concept of a differential and tissue-specific regulation of energy metabolism, which can occur independently of insulin resistance. This trial was registered at clinicaltrials.gov as NCT01229059.
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Affiliation(s)
- Maria Fritsch
- Institute for Clinical Diabetology, German Diabetes Center, Leibniz Center for Diabetes Research, Department of Pediatric and Adolescent Medicine, Medical University of Vienna, Vienna, Austria; and
| | - Chrysi Koliaki
- Institute for Clinical Diabetology, German Diabetes Center, Leibniz Center for Diabetes Research, Department of Endocrinology and Diabetology, Medical Faculty, and German Center of Diabetes Research, Partner Düsseldorf, Germany
| | - Roshan Livingstone
- Institute for Clinical Diabetology, German Diabetes Center, Leibniz Center for Diabetes Research
| | - Esther Phielix
- Institute for Clinical Diabetology, German Diabetes Center, Leibniz Center for Diabetes Research
| | - Alessandra Bierwagen
- Institute for Clinical Diabetology, German Diabetes Center, Leibniz Center for Diabetes Research, German Center of Diabetes Research, Partner Düsseldorf, Germany
| | - Markus Meisinger
- Institute for Clinical Diabetology, German Diabetes Center, Leibniz Center for Diabetes Research
| | - Tomas Jelenik
- Institute for Clinical Diabetology, German Diabetes Center, Leibniz Center for Diabetes Research, German Center of Diabetes Research, Partner Düsseldorf, Germany
| | - Klaus Strassburger
- Institute for Biometrics and Epidemiology, German Diabetes Center, Leibniz Center for Diabetes Research, Heinrich-Heine University, Düsseldorf, Germany, German Center of Diabetes Research, Partner Düsseldorf, Germany
| | - Stefanie Zimmermann
- Institute for Clinical Diabetology, German Diabetes Center, Leibniz Center for Diabetes Research, German Center of Diabetes Research, Partner Düsseldorf, Germany
| | - Katharina Brockmann
- Institute for Clinical Diabetology, German Diabetes Center, Leibniz Center for Diabetes Research, German Center of Diabetes Research, Partner Düsseldorf, Germany
| | - Christina Wolff
- Institute for Clinical Diabetology, German Diabetes Center, Leibniz Center for Diabetes Research, German Center of Diabetes Research, Partner Düsseldorf, Germany
| | - Jong-Hee Hwang
- Institute for Clinical Diabetology, German Diabetes Center, Leibniz Center for Diabetes Research, German Center of Diabetes Research, Partner Düsseldorf, Germany
| | - Julia Szendroedi
- Institute for Clinical Diabetology, German Diabetes Center, Leibniz Center for Diabetes Research, Department of Endocrinology and Diabetology, Medical Faculty, and German Center of Diabetes Research, Partner Düsseldorf, Germany
| | - Michael Roden
- Institute for Clinical Diabetology, German Diabetes Center, Leibniz Center for Diabetes Research, Department of Endocrinology and Diabetology, Medical Faculty, and German Center of Diabetes Research, Partner Düsseldorf, Germany
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Schmid AI, Szendroedi J, Chmelik M, Krssák M, Moser E, Roden M. Liver ATP synthesis is lower and relates to insulin sensitivity in patients with type 2 diabetes. Diabetes Care 2011; 34:448-53. [PMID: 21216854 PMCID: PMC3024365 DOI: 10.2337/dc10-1076] [Citation(s) in RCA: 154] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
OBJECTIVE Steatosis associates with insulin resistance and may even predict type 2 diabetes and cardiovascular complications. Because muscular insulin resistance relates to myocellular fat deposition and disturbed energy metabolism, we hypothesized that reduced hepatic ATP turnover (fATP) underlies insulin resistance and elevated hepatocellular lipid (HCL) contents. RESEARCH DESIGN AND METHODS We measured hepatic fATP using (31)P magnetic resonance spectroscopy in patients with type 2 diabetes and age- and body mass-matched controls. Peripheral (M and M/I) and hepatic (suppression of endogenous glucose production) insulin sensitivity were assessed with euglycemic-hyperinsulinemic clamps. RESULTS Diabetic individuals had 29% and 28% lower peripheral and hepatic insulin sensitivity as well as 42% reduced fATP than controls. After adjusting for HCL, fATP correlated positively with peripheral and hepatic insulin sensitivity but negatively with waist circumference, BMI, and fasting plasma glucose. Multiple regression analysis identified waist circumference as an independent predictor of fATP and inorganic phosphate (P(I)) concentrations, explaining 65% (P = 0.001) and 56% (P = 0.003) of the variations. Hepatocellular P(I) primarily determined the alterations in fATP. CONCLUSIONS In patients with type 2 diabetes, insulin resistance relates to perturbed hepatic energy metabolism, which is at least partly accounted for by fat depots.
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Suzuki A, Ammann P, Nishiwaki-Yasuda K, Sekiguchi S, Asano S, Nagao S, Kaneko R, Hirabayashi M, Oiso Y, Itoh M, Caverzasio J. Effects of transgenic Pit-1 overexpression on calcium phosphate and bone metabolism. J Bone Miner Metab 2010; 28:139-48. [PMID: 19795094 DOI: 10.1007/s00774-009-0121-3] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/18/2008] [Accepted: 08/09/2009] [Indexed: 01/30/2023]
Abstract
The type III inorganic phosphate (Pi) transporter Pit-1 was previously found to be preferentially expressed in developing long bones. Several studies also described a regulation of its expression in cultured bone cells by osteotropic factors, suggesting a role of this transporter in bone metabolism. In the present study, we investigated the effects of the transgenic overexpression of Pit-1 in Wistar male rats on calcium phosphate and bone metabolism. A threefold increase and doubling of Pi transport activity were recorded in primary cultured osteoblastic cells derived from calvaria of two transgenic (Tg) lines compared with wild-type littermates (WT), respectively. Skeletal development was not affected by the transgene, and bone mass, analyzed by DXA, was slightly decreased in Tg compared with WT. Enhanced Pi uptake in calvaria-derived osteoblasts from Pit-1 Tg was associated with a significantly decreased expression of alkaline phosphatase activity and a normal deposition and calcification of the collagenous matrix. In 4-month-old adult Tg rats, serum Pi and renal Pi transport were increased compared with WT. The decrease of serum Ca concentration was associated with increased serum parathyroid hormone levels. Variations in serum Pi in Pit-1 Tg rats were negatively correlated with serum fibroblast growth factor-23, whereas 1,25-dihydroxyvitamin D(3) was not affected by Pit-1 overexpression. In conclusion, transgenic Pit-1 overexpression in rats affected bone and calcium phosphate metabolism. It also decreased alkaline phosphatase activity in osteoblasts without influencing bone matrix mineralization as well as skeletal development.
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Affiliation(s)
- Atsushi Suzuki
- Division of Endocrinology and Metabolism, Department of Internal Medicine, Fujita Health University, 1-98 Dengakugakubo, Kutsukake-cho, Toyoake, Aichi, 470-1192, Japan.
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Xie Z, Li H, Liu L, Kahn BB, Najjar SM, Shah W. Metabolic regulation of Na(+)/P(i)-cotransporter-1 gene expression in H4IIE cells. Am J Physiol Endocrinol Metab 2000; 278:E648-55. [PMID: 10751198 DOI: 10.1152/ajpendo.2000.278.4.e648] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We showed that the rat Na(+)/P(i) cotransporter-1 (RNaPi-1) gene was regulated by insulin and glucose in rat hepatocytes. The aim of this work was to elucidate signaling pathways of insulin-mediated metabolic regulation of the RNaPi-1 gene in H4IIE cells. Insulin increased RNaPi-1 mRNA abundance in the presence of glucose and decreased RNaPi-1 mRNA in the absence of glucose, clearly establishing an involvement of metabolic signals for insulin-induced upregulation of the RNaPi-1 gene. Pyruvate and insulin increased RNaPi-1 expression but downregulated L-pyruvate kinase, indicating the existence of gene-specific metabolic signals. Although fructose, glycerol, and lactate could support insulin-induced upregulation of the RNaPi-1 gene, compounds entering metabolism beyond pyruvate oxidation, such as acetate and citrate, could not, suggesting that RNaPi-1-specific metabolic signals are generated at or above pyruvate oxidation. Wortmannin, LY-294002, and rapamycin abolished the insulin effect on the RNaPi-1 gene, whereas expression of dominant negative Asn(17) Ras and mitogen-activating protein kinase (MAPK) kinase (MEK) inhibitor PD-98059 exhibited no effect. Thus we herein propose that metabolic regulation of RNaPi-1 expression by insulin is mediated through the phosphatidylinositol 3-kinase/p70 ribosomal S6 kinase pathways, but not the Ras/MAPK pathway.
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Affiliation(s)
- Z Xie
- Department of Pharmacology, Medical College of Ohio, Toledo, Ohio 43614-5804, USA.
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7
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Furman S, Lichtstein D, Ilani A. Sodium-dependent transport of phosphate in neuronal and related cells. BIOCHIMICA ET BIOPHYSICA ACTA 1997; 1325:34-40. [PMID: 9106481 DOI: 10.1016/s0005-2736(96)00238-6] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Sodium-dependent phosphate entry into neuronal cells was demonstrated in synaptic plasma membrane vesicles and synaptosomes prepared from rat brains, in PC12 cells and in primary culture of pituitary cells. The extent of the sodium-dependent phosphate transport in the synaptic plasma membrane preparation, at [Na]out = 110 mM and [P(i)]out = 0.1 mM, varied between 0.28 to 1.02 nmol phosphate/mg membrane protein/min. In pituitary cells the value was only about 0.05 nmol P(i)/mg protein/min. In PC12 cells the activity increased from 0.0085 to 0.26 nmol P(i)/mg protein/min in the transit from undifferentiated to differentiated cells. The dependence of phosphate on sodium concentrations fits a model in which two sodium ions are required to transfer the phosphate into the cells with a K[Na]0.5 of 43 mM. The K(m) for the phosphate transport in the synaptic plasma membrane preparations was between 0.1 and 0.45 mM. It is concluded that sodium-driven active transport of phosphate is a ubiquitous activity in various types of neuronal cells.
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Affiliation(s)
- S Furman
- Department of Physiology, The Hebrew University-Hadassah Medical School, Jerusalem, Israel
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Li H, Ren P, Onwochei M, Ruch RJ, Xie Z. Regulation of rat Na+/Pi cotransporter-1 gene expression: the roles of glucose and insulin. THE AMERICAN JOURNAL OF PHYSIOLOGY 1996; 271:E1021-8. [PMID: 8997221 DOI: 10.1152/ajpendo.1996.271.6.e1021] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Cytosolic inorganic phosphate (P(i)) is important for glucose metabolism. It plays a role in homeostatic regulation of glucose by insulin and glucagon. Recently, we isolated two cDNA clones for rat Na+/P(i) cotransporter-1 (rNaPi-1) and demonstrated that they are expressed primarily in the rat liver and kidney. We now report that the expression of rNaPi-1 in these tissues is regulated by fasting and streptozotocin-induced diabetes. Using rat hepatocytes in primary culture, we also demonstrate that glucose and insulin upregulate rNaPi-1 expression, whereas glucagon and elevated intracellular adenosine 3',5'-cyclic monophosphate levels downregulate its expression. Because 2-deoxyglucose exhibits no effect on rNaPi-1 gene expression, we suggest that some metabolite accumulated during glucose metabolism may be responsible for the effects of glucose and insulin on rNaPi-1 gene expression. Our data also reveal that other known Na+/P(i) cotransporter genes, NaPi-2 and Ram-1 (a receptor for amphotropic murine retrovirus), are not regulated by insulin and glucose. It is therefore proposed that various subtypes of Na+/P(i) cotransporters are differentially regulated and that each subtype may be involved in a specific cellular function, rNaPi-1 may be responsible for Pi uptake by liver and kidney for glucose metabolism, whereas NaPi-2 may play a key role in P(i) reabsorption in the kidney.
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Affiliation(s)
- H Li
- Department of Pharmacology, Medical College of Ohio, Toledo 43699-0008, USA
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Younus MJ, Jouhal K, Butterworth PJ. Inhibition by cyclic AMP and phorbol esters of sodium-dependent uptake of phosphate by rat hepatocytes. BIOCHIMICA ET BIOPHYSICA ACTA 1994; 1190:444-8. [PMID: 8142448 DOI: 10.1016/0005-2736(94)90106-6] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Na(+)-dependent phosphate uptake by rat hepatocytes in primary culture is inhibited in a time-dependent fashion by cyclic AMP and by the myristate, acetate ester of phorbol. After incubation for 15 min at 37 degrees C with 10(-7) M dibutyryl cAMP, the Vmax of transport is decreased from 0.52 to 0.23 nmol Pi/min per mg protein but the Km value of approximately 1 mM is hardly affected by the treatment. Thus, physiological control of Pi uptake by liver cells probably involves protein phosphorylation(s) catalysed by protein kinases. Protein kinase C may be important but the relatively high concentration of phorbol ester needed to cause inhibition of transport is not convincing evidence for protein kinase C involvent. In the presence of fructose, the rate of Pi uptake is decreased by 50%. This effect is probably secondary to a depletion of cellular ATP.
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Affiliation(s)
- M J Younus
- Department of Biochemistry, King's College, London, UK
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Younus MJ, Butterworth PJ. Sodium-dependent transport of phosphate by rat liver plasma membrane vesicles. BIOCHIMICA ET BIOPHYSICA ACTA 1993; 1143:158-62. [PMID: 8318517 DOI: 10.1016/0005-2728(93)90138-6] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Plasma membrane fractions were prepared from homogenates of rat liver by density gradient centrifugation and then used for the formation of right-side-out vesicles. Uptake of Pi into the vesicles is rapid when an inwardly directed sodium gradient is present and an overshoot of uptake occurs indicative of accumulation against a Pi concentration gradient. Initial Pi uptake rate in the presence of a K+ gradient is approx half that seen with Na+, but uptake in the presence of a choline chloride gradient is very slow. An overshoot does not occur with either K+ or choline gradients. The Km(Pi) for the Na-dependent component of Pi uptake is approx. 1 mM and Vmax at 20 degrees C is 0.8 nmol/min per mg protein. The relationship between initial uptake rate and Na+ concentration is sigmoid, with a Hill coefficient of 2.6. It is concluded that the cotransporter resembles that of kidney and intestine in possessing at least two interacting sites for Na+ and that in intact cells the Na+ gradient maintained by the sodium pump ATPase provides the energy for accumulation of Pi against the unfavourable membrane potential.
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Affiliation(s)
- M J Younus
- Department of Biochemistry, King's College, London, UK
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