CALCIUM AND PHOSPHORUS IN THE BLOOD AND SKELETON OF THE ELASMOBRANCHII1

Abstract

Elasmobranchii, males as well as females, young and old, normally possessed high concentrations of calcium, 9.0 ± 3.8 meq./L in the serum. The level of calcium in the serum was independent of variations in the blood PCO2, total CO2, HC0₃⁻, pH, total ionic strength, individual major electrolytes, total phosphate, inorganic phosphate, phospholipid, citric acid, urea, or alkaline phosphatasc activity. The protein in the blood was relatively low in concentration, 4.8 ± 1.8 meq./L, had the chemical, electrophoretic, and ultracentrifugal properties of globulin, and showed the capacity to bind 4 mM of calcium per 100 gm. Approximately 75% of the calcium (7.5 ± 1 meq./L) was ultrafilterablc; approximately 85% (6.2 ± 1.5 meq./L) of the calcium in the ultrafiltrate was physiologically active calcium ion as measured by perfusion of the heart of the shark; approximately 93% (7.0 ± 1.5 meq./L) was ionized as measured by the murexide method. The level of inorganic phosphorus was approximately 2.0 ± 0.8 meq./L; only 80%, presumably due to serum protein binding of phosphate, was ultrafilterable. The product of the ionized calcium and diffusible inorganic phosphate was twice that found in serum of bony vertebrates. The physical and chemical factors responsible for the high degree of supersaturation with respect to calcium phosphate in ultrafiltrates of serum require further investigation. Slices of cartilage from rachitic rats incubated in ultrafiltrates produced dense calcification. The calcium deposits in the cartilages of the elasmobranch consisted of an apatite mineral, having a Ca/P molar ratio of 1.52.