Ca(2+) sensing receptor activation by CaCl(2) increases [Ca2+]i resulting in enhanced spatial interactions with calbindin-D28k protein.
The extracellular calcium ion concentration, [Ca2+]o, sensing receptor CaR is a G-protein coupled membrane receptor and it is involved in regulating cell proliferation, differentiation, secretion, and apoptosis. Calbindin-D28k is a high affinity calcium-binding protein that plays important roles in modulating the intracellular calcium ion concentration, [Ca2+]i, and thus influences signal transduction. The role of CaR in sensing and responding to [Ca2+]o and spatial interactions of CaR with calbindin-D28k in a distal tubule-like renal cell line are described. Fura-2 loaded Madin Darby bovine kidney (MDBK) cells were exposed to increasing concentrations of CaCl2 and the [Ca2+]i was determined by ratio fluorescence microscopy. The step-wise addition of CaCl2 caused continual increase in [Ca2+]i. The thapsigargin induced increase in [Ca2+]i observed in basal medium was eliminated by pretreatment of MDBK cells with 10 mM CaCl2 thereby suggesting the involvement of endoplasmic reticulum Ca2+ stores in increasing the [Ca2+]i. CaR was localized in the plasma membrane by using confocal microscopy. The confocal microscopy data also showed CaR and calbindin-D28k were co-localized when cells were exposed to 40 mM CaCl2. We postulate that sensing and responses to increasing [Ca2+]o that occur through CaR, increase the [Ca2+]i causing the translocation of Ca2+-bound calbindin-D28k towards CaR.
Parkash
Jai
J
Department of Anatomy, Joan C Edwards School of Medicine, Marshall University, Huntington, WV 25704, USA. parkash@marshall.edu
Chaudhry
Muhammad A
MA
Rhoten
William B
WB
D000818:Animals; D064092:Calbindin 1; D064026:Calbindins; D002118:Calcium / Q000378:metabolism*; D002122:Calcium Chloride / Q000378:metabolism*; D004721:Endoplasmic Reticulum / Q000378:metabolism; D006801:Humans; D018613:Microscopy, Confocal; D011485:Protein Binding; D044169:Receptors, Calcium-Sensing / Q000378:metabolism; D064030:S100 Calcium Binding Protein G / Q000378:metabolism*
C576498:CALB1 protein, human; D064092:Calbindin 1; D064026:Calbindins; D044169:Receptors, Calcium-Sensing; D064030:S100 Calcium Binding Protein G; D002122:Calcium Chloride; D002118:Calcium