title: Calcium binding to plasma membranes from normal and SV40 transformed hamster lymphocytes.
abstract: The calcium binding properties of isolated plasma membranes from normal and SV40 transformed hamster lymphocytes were compared over the Ca2+ concentration range of 10(-5)M to 5 x 10(-3)M and at physiological ionic strength. At all Ca2+ concentrations, normal membranes bound more Ca2+ than tumor membranes; at blood Ca2+ levels (1-2 mM) plasma membranes of normal cells bind twice as much as membranes from tumor cells. Normal plasma membranes demonstrated positive cooperative Ca2+ binding whereas tumor membranes displayed non-interacting Ca2+ binding sites. Ca2+ binding to both membranes was insensitive to Mg2+ (0.1 to 2.5 mM). A pH shift from 7 to 6 resulted in a 70% decrease of normal membrane-bound Ca2+ compared to a 40% decrease observed with tumor membranes. Extracellular surface Ca2+ binding to intact cells was also studied after a 72-hour equilibration of cells with 45 Ca2+ and with ethyleneglycol-bis-(beta-amino-ethyl ether) N,N'-tetraacetate chelation as marker for surface Ca2+. Tumor cell surface Ca2+ binding was only 10% of that observed with quiescent lymphocytes. Normal lymphocytes stimulated to divide with phytohemagglutinin also showed a decreased level of surface Ca2+ (50%). However, plasma membranes isolated from non-dividing and phytohemagglutinin-stimulated lymphocytes exhibited equivalent Ca2+ binding.
mesh_terms: D000818:Animals; D002118:Calcium / Q000097:blood*; D002462:Cell Membrane / Q000378:metabolism; D002472:Cell Transformation, Viral; D006224:Cricetinae; D006863:Hydrogen-Ion Concentration; D008213:Lymphocyte Activation; D008214:Lymphocytes / Q000378:metabolism*; D008647:Mesocricetus; D013539:Simian virus 40
chemical_list: D002118:Calcium