title: The degree of resistance of erythrocyte membrane cytoskeletal proteins to supra-physiologic concentrations of calcium: an in vitro study.
abstract: Calcium is a key regulator of cell dynamics. Dysregulation of its cytosolic concentration is implicated in the pathophysiology of several diseases. This study aimed to assess the effects of calcium on the network of membrane cytoskeletal proteins. Erythrocyte membranes were obtained from eight healthy donors and incubated with 250 µM and 1.25 mM calcium solutions. Membrane cytoskeletal proteins were quantified using SDS-PAGE at baseline and after 3 and 5 days of incubation. Supra-physiologic concentrations of calcium (1.25 mM) induced a significant proteolysis in membrane cytoskeletal proteins, compared with magnesium (p < 0.001). Actin exhibited the highest sensitivity to calcium-induced proteolysis (6.8 ± 0.3 vs. 5.3 ± 0.6, p < 0.001), while spectrin (39.9 ± 1.0 vs. 40.3 ± 2.0, p = 0.393) and band-6 (6.3 ± 0.3 vs. 6.8 ± 0.8, p = 0.191) were more resistant to proteolysis after incubation with calcium in the range of endoplasmic reticulum concentrations (250 µM). Aggregation of membrane cytoskeletal proteins was determined after centrifugation and was significantly higher after incubation with calcium ions compared with control, EDTA and magnesium solutions (p < 0.001). In a supra-physiologic range of 1.25-10 mM of calcium ions, there was a nearly perfect linear relationship between calcium concentration and aggregation of erythrocyte membrane cytoskeletal proteins (R(2) = 0.971, p < 0.001). Our observation suggests a strong interaction between calcium ions and membrane cytoskeletal network. Cumulative effects of disrupted calcium homeostasis on cytoskeletal proteins need to be further investigated at extended periods of time in disease states.
authors.affiliation: Department of Laboratory Medicine, Mirza Kouchak Khan Women's Hospital, Tehran University of Medical Sciences, Tehran, Iran, eb_mostafavi@yahoo.com.
authors.forename: Ebrahim
authors.initials: E
authors.lastname: Mostafavi
authors.forename: Arash Aghajani
authors.initials: AA
authors.lastname: Nargesi
authors.forename: Zaniar
authors.initials: Z
authors.lastname: Ghazizadeh
authors.forename: Mehrdad
authors.initials: M
authors.lastname: Larry
authors.forename: Roya Horabad
authors.initials: RH
authors.lastname: Farahani
authors.forename: Afsaneh
authors.initials: A
authors.lastname: Morteza
authors.forename: Alireza
authors.initials: A
authors.lastname: Esteghamati
authors.forename: Claude
authors.initials: C
authors.lastname: Vigneron
authors.forename: Manouchehr
authors.initials: M
authors.lastname: Nakhjavani
mesh_terms: D000199:Actins / Q000378:metabolism*; D001457:Anion Exchange Protein 1, Erythrocyte / Q000378:metabolism*; D002118:Calcium / Q000494:pharmacology*; D003598:Cytoskeletal Proteins / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D004910:Erythrocyte Membrane / Q000187:drug effects / Q000378:metabolism*; D006801:Humans; D066298:In Vitro Techniques; D013049:Spectrin / Q000378:metabolism*
chemical_list: D000199:Actins; D001457:Anion Exchange Protein 1, Erythrocyte; D003598:Cytoskeletal Proteins; C454201:SLC4A1 protein, human; D013049:Spectrin; D002118:Calcium