The major goal of this research project is to elucidate the cellular mechanisms by which phosphate (Pi) is reabsorbed from the lumen of proximal tubules across the brush border membrane (BBM). The investigations are based on the general hypothesis that: (A). Na+-gradient-dependent uptake of Pi at luminal BBM is of higher capacity in early proximal convoluted tubules (PCT) and is determined mainly by dietary phosphorus (P) intake, whereas in late proximal straight segments - pars recta (PR) it is of lower capacity and is regulated mainly by hormonal stimuli; (B). that long-term """"""""adaptive"""""""" stimuli regulate Pi transport across BBM by changing rate or mode of biogenesis of the Na-Pi cotransporter (Na-Pi-COT) of BBM, whereas short-term """"""""rapid"""""""" stimuli act by the changing balance between Na-Pi-COT within BBM and Na-P-COT in cytoplasmic depot vesicles - recycling of Na-Pi-COT. Specific objectives of the planned research include: 1). To isolate the BBM vesicles (BBMV) containing Na+-Pi-COT specifically from early proximal segments (PCT) and from the late proximal segments (PR). 2). To determine intramembranous localization of Na-Pi-COT within BBM, and the major biochemical components involved in its function and regulation. 3). To elucidate the biogenesis of the Na-Pi-COT in BBM from PCT and PR. To determine incorporation of amino acid and monosaccharide precursors into Na-P-COT of BBM; these studies will be conducted on renal preparations in vitro and in vivo. 4). To determine the cellular mechanism of action of a) long-term adaptive stimuli (dietary Pi intake, glucocorticoids, thyroxine) and b) rapid modulatory stimuli (PTH, calcitonin, acute Pi load) on biogenesis and recycling of Na-Pi-COT. We will examine whether long-term stimuli modify the rate of synthesis or the mode of post-translational modification of Na-Pi-COT, whereas, rapid stimuli modulate the balance between active Na-Pi-COT inserted into BBM and nonfunctional Na-Pi-COT located in cytoplasmic vesicles (membrane recycling). These regulatory mechanisms will be examined separately in BBM from PCT and BBM from PR. 5). To determine the biochemical nature, intramembranous BBM localization, and axial nephron localization of the Na-Pi-COT defect occurring in the murine model of X-linked hypophosphatemic rickets (""""""""Hyp-mice"""""""").

Agency
National Institute of Health (NIH)
Institute
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Type
Method to Extend Research in Time (MERIT) Award (R37)
Project #
5R37DK030759-09
Application #
3483584
Study Section
General Medicine B Study Section (GMB)
Project Start
1982-04-01
Project End
1991-03-31
Budget Start
1990-04-01
Budget End
1991-03-31
Support Year
9
Fiscal Year
1990
Total Cost
Indirect Cost
Name
Mayo Clinic, Rochester
Department
Type
DUNS #
City
Rochester
State
MN
Country
United States
Zip Code
55905
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Caride, A J; Chini, E N; Penniston, J T et al. (1999) Selective decrease of mRNAs encoding plasma membrane calcium pump isoforms 2 and 3 in rat kidney. Kidney Int 56:1818-25
de Toledo, F G; Thompson, M A; Bolliger, C et al. (1999) gamma-L-glutamyl-L-DOPA inhibits Na(+)-phosphate cotransport across renal brush border membranes and increases renal excretion of phosphate. Kidney Int 55:1832-42
Caride, A J; Chini, E N; Homma, S et al. (1998) mRNAs coding for the calcium-sensing receptor along the rat nephron: effect of a low-phosphate diet. Kidney Blood Press Res 21:305-9
Chini, E N; de Toledo, F G; Thompson, M A et al. (1997) Effect of estrogen upon cyclic ADP ribose metabolism: beta-estradiol stimulates ADP ribosyl cyclase in rat uterus. Proc Natl Acad Sci U S A 94:5872-6
de Toledo, F G; Beers, K W; Berndt, T J et al. (1997) Opposite paracrine effects of 5-HT and dopamine on Na(+)-Pi cotransport in opossum kidney cells. Kidney Int 52:152-6
de Toledo, F G; Cheng, J; Dousa, T P (1997) Retinoic acid and triiodothyronine stimulate ADP-ribosyl cyclase activity in rat vascular smooth muscle cells. Biochem Biophys Res Commun 238:847-50
Beers, K W; Thompson, M A; Chini, E N et al. (1996) beta-Estradiol inhibits Na+-P(i) cotransport across renal brush border membranes from ovarectomized rats. Biochem Biophys Res Commun 221:442-5
Beers, K W; Chini, E N; Lee, H C et al. (1995) Metabolism of cyclic ADP-ribose in opossum kidney renal epithelial cells. Am J Physiol 268:C741-6

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