Calcium sensing receptor activation by a calcimimetic suggests a link between cooperativity and intracellular calcium oscillations

Susanne Miedlich, Lucio Gama, Gerda E. Breitwieser

Research output: Contribution to journalArticlepeer-review

42 Scopus citations


Activation of the calcium sensing receptor (CaR) by small increments in extracellular calcium (Ca2+e) induces intracellular calcium (Ca2+i) oscillations that are dependent on thapsigargin-sensitive intracellular calcium stores. Phenylalkylamines such as NPS R-568 are allosteric modulators (calcimimetics) that activate CaR by increasing the apparent affinity of the receptor for calcium. We determined, by fluorescence imaging with fura-2, whether the calcimimetic NPS R-568 could activate Ca2+i oscillations in HEK-293 cells expressing human CaR. NPS R-568 was more potent than Ca2+e at eliciting Ca2+i oscillations, particularly at low [Ca2+]e (as low as 0.1 mM). The oscillation frequencies elicited by NPS R-568 varied over a 2-fold range from peak to peak intervals of 60-70 to 30-45 s, depending upon the concentrations of both Ca2+e and NPS R-568. Finally, NPS R-568 induced sustained (>15 min after drug removal) Ca2+i oscillations, suggesting slow release of the drug from its binding site. We exploited the potency of NPS R-568 for eliciting Ca2+i oscillations for structural studies. Truncation of the CaR carboxyl terminus from 1077 to 886 amino acids had no effect on the ability of Ca2+ or NPS R-568 to induce Ca2+i oscillations, but further truncation (to 868 amino acids) eliminated both highly cooperative Ca2+-dependent activation and regular Ca2+i oscillations. Alanine scanning within the amino acid sequence from Arg873 to His879 reveals a linkage between the cooperativity for Ca2+-dependent activation and establishment and maintenance of intracellular Ca2+ oscillations. The amino acid residues critical to both functions of CaR may contribute to interactions with either G proteins or between CaR monomers within the functional dimer.

Original languageEnglish (US)
Pages (from-to)49691-49699
Number of pages9
JournalJournal of Biological Chemistry
Issue number51
StatePublished - Dec 20 2002
Externally publishedYes

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology


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