Inorganic phosphate (Pi) filtered by the kidney is reabsorbed primarily in the proximal tubule. The initial and possibly rate-limiting step in this process is Na-dependent transport of Pi across the luminal brush border membrane (BBM) of the proximal tubule. The capacity of the BBM for Pi transport is altered in response to changes in the dietary Pi intake and to various hormones and drugs. While other factors may contribute to the regulation of renal Pi reabsorption, a specific deficiency in the adaptive mechanism of the Pi transport system in the BBM has serious consequences for Pi homeostasis. The long-term objective of the current proposal is to understand the cellular regulation of Na-dependent Pi transport across the renal BBM. Treatment of rats with nicotinamide leads to an increase in the NAD level in the proximal tubule and, accompanying this change, there is specific inhibition of Na-dependent Pi transport across the BBM and an increase in urinary Pi excretion.
The specific aim of this proposal is to investigate whether NAD is used for ADP-ribosylation of the cytosolic surface of the BBM, by what mechanism, whether this process causes specific inhibition of Na-dependent Pi transport across the BBM, and whether there are enzyme-catalysed reactions for reversal of ADP-ribosylation. The studies which will address these questions will be carried out largely in vitro using isolated BBM preparations. The BBM will be ADP-ribosylated with either NAD or ADP-ribose and Pi transport will be assessed as uptake of radiolabelled Pi in the presence of a transmembrane sodium gradient. Uptake of other solutes, such as glucose and amino acids, will be monitored to establish the specificity of any changes in Pi transport. Reversal of ADP-ribosylation will be studied using BBM ribosylated with radiolabelled NAD. The BBM will be incubated with various cell fractions and the radiolabelled material which is released will be measured and identified.

Agency
National Institute of Health (NIH)
Institute
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Type
Research Project (R01)
Project #
5R01DK032148-05
Application #
3230601
Study Section
General Medicine B Study Section (GMB)
Project Start
1982-09-01
Project End
1989-06-30
Budget Start
1987-07-01
Budget End
1988-06-30
Support Year
5
Fiscal Year
1987
Total Cost
Indirect Cost
Name
Indiana University-Purdue University at Indianapolis
Department
Type
Schools of Medicine
DUNS #
005436803
City
Indianapolis
State
IN
Country
United States
Zip Code
46202
Andreoli, S P; Mallett, C P; McAteer, J A et al. (1998) Epidermal growth factor accelerates recovery of LLC-PK1 cells following oxidant injury. In Vitro Cell Dev Biol Anim 34:824-30
Chen, J G; Hinesley, R; Kempson, S A (1997) Dual action of colchicine on hypertonic activation of system A amino acid transport in vascular smooth muscle cells. Life Sci 61:29-37
Chen, J G; Coe, M; McAteer, J A et al. (1996) Hypertonic activation and recovery of system A amino acid transport in renal MDCK cells. Am J Physiol 270:F419-24
Kempson, S A (1996) Peptide hormone action on renal phosphate handling. Kidney Int 49:1005-9
Levi, M; Kempson, S A; Lotscher, M et al. (1996) Molecular regulation of renal phosphate transport. J Membr Biol 154:1-9
Chen, J G; Strawbridge, A B; Kempson, S A (1995) Microtubule disruption stimulates system A transport in cultured vascular smooth muscle cells. Am J Physiol 268:C1512-9
Chen, J G; Kempson, S A (1995) Osmoregulation of neutral amino acid transport. Proc Soc Exp Biol Med 210:1-6
Kempson, S A; Lotscher, M; Kaissling, B et al. (1995) Parathyroid hormone action on phosphate transporter mRNA and protein in rat renal proximal tubules. Am J Physiol 268:F784-91
Paraiso, M S; McAteer, J A; Kempson, S A (1995) Parathyroid hormone inhibits plasma membrane Pi transport without changing endocytic activity in opossum kidney cells. Biochim Biophys Acta 1266:143-7
Werner, A; Kempson, S A; Biber, J et al. (1994) Increase of Na/Pi-cotransport encoding mRNA in response to low Pi diet in rat kidney cortex. J Biol Chem 269:6637-9

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