PATTERNS OF CALCIUM DISTRIBUTION BY BIOCHEMICAL SERUM COMPARTMENTS IN VITRO MODELING OF MINERAL STRESS IN THE CONTEXT OF ENDOTHELIAL DYSFUNCTION
Authors: Shishkova Daria K. , Markova Victoria E. , Markova Yulia O. , Torgunakova Evgeniya A. , Kondratiev Egor A. , Dyleva Yulia A. , Kutikhin Anton G. 
Published: July 2024

Highlights

When modeling mineral stress, a closed biochemical system shows the following calcium distribution ratio among biochemical compartments: freely circulating ions (Ca2+) – 50%, bound to albumin (CPM) - 20%, bound to and phosphorus (CPC) - 30%.

The ratio of ionized to protein- or phosphorus-bound calcium was 1:1 and corresponded to the physiological ratio of ionized to bound calcium in circulating blood, indicating the physiological relevance of the simulations performed.

Even under supraphysiological mineral stress, natural mineral depots (CPM and HRC) maintain the calcium-binding capacity of the biochemical system at the physiological level (50%), and the ratio of the relative calcium capacity of the CPM and HRC under conditions of supraphysiological mineral stress indicates the priority role of the HRC as a buffer system limiting the uncontrolled increase in ionized calcium in case of disturbance of the mineral balance of the blood.

 

Abstract

Aim. To conduct a comparative analysis of calcium content in various biochemical compartments: 1) ionized (freely circulating, unbound) calcium; 2) calcium-albumin CPM (protein-bound calcium); 3) calcium phosphorus complexes (CPC).

Methods. In order to prepare a biochemical system for the parallel synthesis of CPM and CPC, supraphysiological mineral stress was modeled by supersaturating a NaCl saline solution containing a physiological concentration of albumin with calcium (CaCl2) and phosphorus (Na2HPO4) ions. Separation of calcium-containing biochemical compartments was carried out by ultracentrifugation (to isolate CPM) and ultrafiltration (to separate CPM and the pool of free ions). Calcium concentration was measured using a colorimetric method based on the reaction of orthocresolphthalein complexone with calcium ions in an alkaline medium.

Results. When modeling mineral stress, a closed biochemical system was obtained in which calcium ions were freely distributed in three states: circulating in free form (Ca2+) or being part of the CPM (colloidal primary depot) or PSC (corpuscular secondary depot). The distribution of calcium in the form of freely circulating ions (Ca2+) and when bound to albumin (CPM) and phosphorus (CPC) was 50%: 20%: 30% (5: 2: 3), respectively. The ratio of ionized to protein- or phosphorus-bound calcium was 1:1 and corresponded to the physiological ratio of ionized to bound calcium in circulating blood, indicating the physiological relevance of the simulations performed. The formation of HRC absorbed 10 to 20% of the total albumin.

Conclusion. Even under supraphysiological mineral stress, natural mineral depots (CPM and HRC) maintain the calcium-binding capacity of the biochemical system at the physiological level (50%), and the ratio of the relative calcium capacity of the CPM and HRC under conditions of supraphysiological mineral stress indicates the priority role of the HRC as a buffer system limiting the uncontrolled increase in ionized calcium in case of disturbance of the mineral balance of the blood.