Age-related changes in composition and Ca2+-binding capacity of canine cortical bone extracts.
The variable of age was used to study macromolecules in bone that may mediate in part the in vivo readily exchangeable calcium-binding capacity (VCa2+D). Organic components were extracted from nonmineralized bone with 4 M guanidine-HCl and from both nonmineralized and mineralized bone with 0.1 M EDTA. The composition of pup bone extracts demonstrated an enrichment in protein, hexuronate, sialic acid, organic phosphorus, and bound sulfate when compared with other age groups. In vitro calcium-binding studies identified low-affinity (Kd congruent to 10(-3) M) sites in both types of extracts; high-affinity sites (Kd congruent to 10(-5) M) were only evident in EDTA extracts of bone. Readily exchangeable calcium-binding capacity in vivo was found to decrease from pup (40.7 mM) to adolescent (11.1 mM) to the mature/old groups (2.6/1.2 mM); however, a large difference in low-affinity site number was only observed between pup and adolescent bone extracts. The overall organic composition of EDTA and guanidine-HCl extracts generally reflected the composition of total bone, which dropped dramatically on a dry weight basis from pup to adolescent groups. A similar pattern was observed with the number of low-affinity binding sites measured in vitro. In vitro binding data indicate that nonmineralized matrix of pup bone, extractable by 4 M guanidine-HCl, possesses enough capacity to accommodate approximately 40% of the readily exchangeable pool. As age progresses, other components of the blood-bone exchange process, such as vascularity, may reduce the readily exchangeable calcium pool size below the amount of low-affinity sites measured in vitro.
D000375:Aging; D000818:Animals; D001665:Binding Sites; D001842:Bone and Bones / Q000032:analysis / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D002810:Chondroitinases and Chondroitin Lyases / Q000378:metabolism; D004285:Dogs; D004492:Edetic Acid; D005260:Female; D019791:Guanidine; D006146:Guanidines; D008297:Male; D008970:Molecular Weight; D012016:Reference Values; D013395:Sucrose / Q000032:analysis
D006146:Guanidines; D013395:Sucrose; D004492:Edetic Acid; D002810:Chondroitinases and Chondroitin Lyases; D019791:Guanidine; D002118:Calcium