Transport and distribution of 45Ca2 + in the perfused rat liver and the influence of adjuvant-induced arthritis

Abstract

The purpose of the present work was to investigate Ca2+ 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 45Ca2+ 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 45Ca2+ outflow profiles corresponds to a model that assumes rapid distribution of 45Ca2+ 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 Ca2+ 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 Ca2+ concentration in the hormone-sensitive cellular pool. Furthermore, reduced rates of Ca2+ 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 Ca2+-ATPase (SERCA2) protein. All these observations mean that in livers from arthritic rats more time is required to replenish the hormone sensitive Ca2+ stores.