Calcium transport from blood into the bile in normal and regenerating rat liver

We have studied calcium movement from blood into the bile by injecting 45Ca2+ intravenously and measuring the radioactivity appearing in the bile. 45Ca2+ started to appear in the bile at 3 min and maximum values were observed at 5 min after its administration. The amount of calcium secreted into the bile was proportional to the blood calcium concentration indicating that the main pathway involved in calcium movement behaved as a non-saturable system. We have also studied the 45Ca2+ circulation from blood into the bile in rats subjected to a partial hepatectomy. Thereafter, the calcium transported into the bile per gram of liver increased by about 50 per cent. Since bile flow behaved in a similar way, the biliar calcium concentration remained unmodified after hepatectomy. Determination of the activities of the Ca2+ transporting systems in isolated plasma membrane fractions from regenerating livers showed no modification in these activities suggesting that the elevation in calcium movement observed after hepatectomy is not due to an increase in the circulation of Ca2+ through the transhepatocyte pathway, an observation compatible with the absence of saturation in the transport.