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Pflugers Arch. 2018 Nov 5. doi: 10.1007/s00424-018-2231-z. [Epub ahead of print]

Physiological regulation of phosphate by vitamin D, parathyroid hormone (PTH) and phosphate (Pi).

Author information

1
Centre for Nephrology, University College London (UCL), Royal Free Campus, Rowland Hill Street, London, NW3 2PF, UK.
2
Centre for Nephrology, University College London (UCL), Royal Free Campus, Rowland Hill Street, London, NW3 2PF, UK. robert.unwin@ucl.ac.uk.
3
AstraZeneca IMED ECD CVRM R&D, Gothenburg, Sweden. robert.unwin@ucl.ac.uk.

Abstract

Inorganic phosphate (Pi) is an abundant element in the body and is essential for a wide variety of key biological processes. It plays an essential role in cellular energy metabolism and cell signalling, e.g. adenosine and guanosine triphosphates (ATP, GTP), and in the composition of phospholipid membranes and bone, and is an integral part of DNA and RNA. It is an important buffer in blood and urine and contributes to normal acid-base balance. Given its widespread role in almost every molecular and cellular function, changes in serum Pi levels and balance can have important and untoward effects. Pi homoeostasis is maintained by a counterbalance between dietary Pi absorption by the gut, mobilisation from bone and renal excretion. Approximately 85% of total body Pi is present in bone and only 1% is present as free Pi in extracellular fluids. In humans, extracellular concentrations of inorganic Pi vary between 0.8 and 1.2 mM, and in plasma or serum Pi exists in both its monovalent and divalent forms (H2PO4- and HPO42-). In the intestine, approximately 30% of Pi absorption is vitamin D regulated and dependent. To help maintain Pi balance, reabsorption of filtered Pi along the renal proximal tubule (PT) is via the NaPi-IIa and NaPi-IIc Na+-coupled Pi cotransporters, with a smaller contribution from the PiT-2 transporters. Endocrine factors, including, vitamin D and parathyroid hormone (PTH), as well as newer factors such as fibroblast growth factor (FGF)-23 and its coreceptor α-klotho, are intimately involved in the control of Pi homeostasis. A tight regulation of Pi is critical, since hyperphosphataemia is associated with increased cardiovascular morbidity in chronic kidney disease (CKD) and hypophosphataemia with rickets and growth retardation. This short review considers the control of Pi balance by vitamin D, PTH and Pi itself, with an emphasis on the insights gained from human genetic disorders and genetically modified mouse models.

KEYWORDS:

Epithelial transport; Homeostasis; Kidney physiology; Phosphate; Proximal tubule; Renal

PMID:
30393837
DOI:
10.1007/s00424-018-2231-z

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