Non-diffusible serum-calcium at various calcium, phosphate and hydrogen ion concentrations

Abstract

When CaCl2 was added to normal dog''s serum in vitro the relation between the newly-formed non-diffusible Ca and non-diffusible inorganic PO4 expressed as Ca/P was consistently higher than Ca/P in such compounds as CaHPO4 and Ca3(PO4)2, indicating that Ca was combined with some substance other than PO4[long dash] presumably protein[long dash]and that these 2 combinations occurred simultaneously as the Ca content of the serum was gradually increased. When Ca was added to serum in the presence of excess PO4 this ratio was 1.9, equivalent to Ca/P in Ca3(PO4)2. Apparently no direct combination between Ca and protein took place under this condition. A change in pH from 8 to 7 caused an increase in the diffusible Ca of normal serum of approx. 7% of the total Ca. In serum with Ca added this increase was greater (15%) explainable by the fact that under such conditions a considerable part of the non-diffusible Ca is Ca3(PO4)2 which breaks down over this pH range, freeing Ca to the diffusible form. With Ca added to serum in the presence of excess PO4 the increase was still greater[long dash] approx. 32%[long dash]as in this case much the greater part of the non-diffusible Ca is in the form of Ca3(PO4)2.