BACKGROUND: Aluminum (Al3+) has diverse biological effects mediated through activation of a putative extracellular cation-sensing receptor. A recently identified calcium-sensing receptor (CaSR), which has been identified in target tissues for Al3+, may transduce some of the biological effects of Al3+. METHODS: To test this possibility, we transfected human embryonic kidney 293 (HEK 293) cells with a cDNA encoding the rat CaSR and evaluated CaSR expression by Western blot analysis and function by measurement of intracellular calcium ([Ca2+]i) levels and inositol monophosphate (IP1) generation following stimulation with Al3+ and a panel of CaSR agonists. RESULTS: The CaSR protein was detected by immunoblot analysis in cells transfected with the CaSR cDNA but not in nontransfected HEK 293 cells. In addition, [Ca2+]i levels and IP1 generation were enhanced in a dose-dependent fashion by additions of the CaSR agonists calcium (Ca2+), magnesium (Mg2+), gadolinium (Gd3+), and neomycin only in cells transfected with CaSR. To determine if Al3+ activated CaSR, we stimulated cells transfected with rat CaSR with 10 microM to 1 mM concentrations of Al3+. Concentrations of Al3+ in the range of 10 microM to 100 microM had no effect on [Ca2+]i levels or IP1 generation. In contrast, 1 mM Al3+ induced small but significant increases in both parameters. Whereas Gd3+ antagonized calcium-mediated activation of CaSR, pretreatment with Al3+ failed to block subsequent activation of rat CaSR by Ca2+, suggesting a distinct mechanism of Al3+ action. CONCLUSION: Al3+ is not a potent agonist for CaSR. Because Al3+ affects a variety of target tissues at micromolar concentrations, it seems unlikely that CaSR mediates these cellular actions of Al3+.
BACKGROUND:Aluminum (Al3+) has diverse biological effects mediated through activation of a putative extracellular cation-sensing receptor. A recently identified calcium-sensing receptor (CaSR), which has been identified in target tissues for Al3+, may transduce some of the biological effects of Al3+. METHODS: To test this possibility, we transfected humanembryonic kidney 293 (HEK 293) cells with a cDNA encoding the ratCaSR and evaluated CaSR expression by Western blot analysis and function by measurement of intracellular calcium ([Ca2+]i) levels and inositol monophosphate (IP1) generation following stimulation with Al3+ and a panel of CaSR agonists. RESULTS: The CaSR protein was detected by immunoblot analysis in cells transfected with the CaSR cDNA but not in nontransfected HEK 293 cells. In addition, [Ca2+]i levels and IP1 generation were enhanced in a dose-dependent fashion by additions of the CaSR agonists calcium (Ca2+), magnesium (Mg2+), gadolinium (Gd3+), and neomycin only in cells transfected with CaSR. To determine if Al3+ activated CaSR, we stimulated cells transfected with ratCaSR with 10 microM to 1 mM concentrations of Al3+. Concentrations of Al3+ in the range of 10 microM to 100 microM had no effect on [Ca2+]i levels or IP1 generation. In contrast, 1 mM Al3+ induced small but significant increases in both parameters. Whereas Gd3+ antagonized calcium-mediated activation of CaSR, pretreatment with Al3+ failed to block subsequent activation of ratCaSR by Ca2+, suggesting a distinct mechanism of Al3+ action. CONCLUSION:Al3+ is not a potent agonist for CaSR. Because Al3+ affects a variety of target tissues at micromolar concentrations, it seems unlikely that CaSR mediates these cellular actions of Al3+.
Authors: Min Pi; Pieter Faber; George Ekema; P David Jackson; Anthony Ting; Nancy Wang; Michelle Fontilla-Poole; Robert W Mays; Kurt R Brunden; John J Harrington; L Darryl Quarles Journal: J Biol Chem Date: 2005-09-30 Impact factor: 5.157