Pathophysiological Changes in Extracellular pH Regulate Calcium-Sensing Receptor Activity in HEK-293 and Isolated Parathyroid Cells

Wanda D McCormick, Donald T Ward

    Research output: Contribution to conferencePoster

    Abstract

    INTRODUCTION AND AIMS:Mammalian extracellular calcium (Ca2+o) concentration is maintained by parathyroid hormone (PTH) secretion under the control of the calcium-sensing receptor (CaR). Elevated PTH secretion is a complication of chronic renal failure (CRF) as indeed is metabolic acidosis. Interestingly, acidosis is associated with increased PTH secretion in humans and dogs (1) while in CaR stably-transfected human embryonic kidney (CaR-HEK) cells, large changes in extracellular pH (pHo) alter CaR agonist sensitivity (2). To examine whether smaller, pathophysiological changes in pHo also cause significant changes in CaR activity, and not only in heterologous but also endogenous expression systems, the effect of 0.2 unit pHo changes were tested on intracellular Ca2+ (Ca2+i) mobilisation in CaR-HEK and isolated bovine parathyroid cells.METHODS:Bovine superior parathyroid glands were digested with collagenase and viable parathyroid cells collected using a self-forming Percoll gradient. [Ca2+]i and pHi were measured by epifluorescence microscopy using Fura2 and BCECF respectively.RESULTS:CaR-HEK cells were stimulated with 2.5mM Ca2+o (pH 7.4) to elicit CaR-induced Ca2+i mobilisation and then switched to the same buffer at either pH 7.2 (acidosis)or 7.6 (alkalosis) resulting in rapidly attenuated (-59??7%; N=7; P=0.012) or elevated (+31??9; N=8; P=0.011) responses respectively. Both pHo-induced effects were found to be rapidly reversible upon return to the pH 7.4 buffer. Similarly, where extracellular signal-regulated kinase (ERK) phosphorylation was used as an alternative readout of CaR activity, acidosis attenuated the activation of ERK (induced by 3.5mM Ca2+o) by 56??11% (N=9; P
    Original languageEnglish
    Publication statusPublished - 23 May 2009
    EventWorld Congress of Nephrology 2009 - Milan, Italy
    Duration: 22 May 200926 May 2009

    Conference

    ConferenceWorld Congress of Nephrology 2009
    CityMilan, Italy
    Period22/05/0926/05/09

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