title: Pathophysiologic Changes in Extracellular pH Modulate Parathyroid Calcium-Sensing Receptor Activity and Secretion via a Histidine-Independent Mechanism.
abstract: The calcium-sensing receptor (CaR) modulates renal calcium reabsorption and parathyroid hormone (PTH) secretion and is involved in the etiology of secondary hyperparathyroidism in CKD. Supraphysiologic changes in extracellular pH (pHo) modulate CaR responsiveness in HEK-293 (CaR-HEK) cells. Therefore, because acidosis and alkalosis are associated with altered PTH secretion in vivo, we examined whether pathophysiologic changes in pHo can significantly alter CaR responsiveness in both heterologous and endogenous expression systems and whether this affects PTH secretion. In both CaR-HEK and isolated bovine parathyroid cells, decreasing pHo from 7.4 to 7.2 rapidly inhibited CaR-induced intracellular calcium (Ca(2+)i) mobilization, whereas raising pHo to 7.6 potentiated responsiveness to extracellular calcium (Ca(2+)o). Similar pHo effects were observed for Ca(2+)o-induced extracellular signal-regulated kinase phosphorylation and actin polymerization and for L-Phe-induced Ca(2+)i mobilization. Intracellular pH was unaffected by acute 0.4-unit pHo changes, and the presence of physiologic albumin concentrations failed to attenuate the pHo-mediated effects. None of the individual point mutations created at histidine or cysteine residues in the extracellular domain of CaR attenuated pHo sensitivity. Finally, pathophysiologic pHo elevation reversibly suppressed PTH secretion from perifused human parathyroid cells, and acidosis transiently increased PTH secretion. Therefore, pathophysiologic pHo changes can modulate CaR responsiveness in HEK-293 and parathyroid cells independently of extracellular histidine residues. Specifically, pathophysiologic acidification inhibits CaR activity, thus permitting PTH secretion, whereas alkalinization potentiates CaR activity to suppress PTH secretion. These findings suggest that acid-base disturbances may affect the CaR-mediated control of parathyroid function and calcium metabolism in vivo.
authors.affiliation: Faculty of Life Sciences, The University of Manchester, Manchester, United Kingdom;
authors.forename: Katherine L
authors.initials: KL
authors.lastname: Campion
authors.affiliation: Faculty of Life Sciences, The University of Manchester, Manchester, United Kingdom; Animal Welfare, Moulton College, Northamptonshire, United Kingdom;
authors.forename: Wanda D
authors.initials: WD
authors.lastname: McCormick
authors.affiliation: Faculty of Life Sciences, The University of Manchester, Manchester, United Kingdom;
authors.forename: Jim
authors.initials: J
authors.lastname: Warwicker
authors.affiliation: Faculty of Life Sciences, The University of Manchester, Manchester, United Kingdom; Department of Biochemistry, Faculty of Biotechnology and Biomolecular Sciences, Universiti Putra Malaysia, Selangor, Malaysia; and.
authors.forename: Mohd Ezuan Bin
authors.initials: ME
authors.lastname: Khayat
authors.affiliation: Faculty of Life Sciences, The University of Manchester, Manchester, United Kingdom;
authors.forename: Rebecca
authors.initials: R
authors.lastname: Atkinson-Dell
authors.affiliation: Faculty of Life Sciences, The University of Manchester, Manchester, United Kingdom;
authors.forename: Martin C
authors.initials: MC
authors.lastname: Steward
authors.affiliation: School of Molecular Bioscience, University of Sydney, New South Wales, Australia.
authors.forename: Leigh W
authors.initials: LW
authors.lastname: Delbridge
authors.affiliation: School of Molecular Bioscience, University of Sydney, New South Wales, Australia.
authors.forename: Hee-Chang
authors.initials: HC
authors.lastname: Mun
authors.affiliation: School of Molecular Bioscience, University of Sydney, New South Wales, Australia.
authors.forename: Arthur D
authors.initials: AD
authors.lastname: Conigrave
authors.affiliation: Faculty of Life Sciences, The University of Manchester, Manchester, United Kingdom; d.ward@manchester.ac.uk.
authors.forename: Donald T
authors.initials: DT
authors.lastname: Ward
mesh_terms: D000138:Acidosis / Q000378:metabolism; D000471:Alkalosis / Q000378:metabolism; D000818:Animals; D002417:Cattle; D003545:Cysteine / Q000235:genetics / Q000378:metabolism; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism*; D057809:HEK293 Cells; D006639:Histidine / Q000235:genetics / Q000378:metabolism; D006801:Humans; D006863:Hydrogen-Ion Concentration; D010280:Parathyroid Glands / Q000378:metabolism*; D010281:Parathyroid Hormone / Q000378:metabolism*; D010766:Phosphorylation; D044169:Receptors, Calcium-Sensing / Q000378:metabolism*
chemical_list: D010281:Parathyroid Hormone; D044169:Receptors, Calcium-Sensing; D006639:Histidine; D048049:Extracellular Signal-Regulated MAP Kinases; D003545:Cysteine
keywords: acidosis.; calcium-sensing receptor; hyperparathyroidism; mineral metabolism; parathyroid hormone