Transport and distribution of (45)Ca(2+) in the perfused rat liver and the influence of adjuvant-induced arthritis

Abstract

The purpose of the present work was to investigate Ca(2+) transport and distribution under the conditions of the intact rat liver in health and disease (adjuvant-induced arthritis). The multiple-indicator dilution technique was used with the simultaneous injection of (45)Ca(2+) and indicators into the portal vein under defined conditions and analysis of the outflow profiles by means of a space-distributed variable transit time model. The best description of the (45)Ca(2+) outflow profiles corresponds to a model that assumes rapid distribution of (45)Ca(2+) between the vascular space and the cell surface and a slower transfer into the hepatocytes. In kinetic terms two distinct cellular pools were distinguishable, the cytosol and the endoplasmic reticulum. The concentration of Ca(2+) in the cytosol was much lower than in the vascular space and in the endoplasmic reticulum. The most prominent modification observed in the livers of arthritic rats was the increased Ca(2+) concentration in the hormone-sensitive cellular pool. Furthermore, reduced rates of Ca(2+) influx and efflux between the hormone-sensitive cellular pool and the cytosolic space were also detected in combination with a significantly reduced expression of the sarco-endoplasmic reticulum Ca(2+)-ATPase (SERCA2) protein. All these observations mean that in livers from arthritic rats more time is required to replenish the hormone sensitive Ca(2+) stores.