BILE-ACIDS MOBILIZE INTERNAL CA-2+ INDEPENDENTLY OF EXTERNAL CA-2+ IN RAT HEPATOCYTES

In the present study, we investigated the possible role of external Ca2+ in the rise of the cytosolic Ca+ concentration induced by the monohydroxy bile acid taurolithocholate in isolated rat liver cells. The results showed that: (a) the bile acid promotes the same dose‐dependent increase in the cytosolic Ca+ concentration (half‐maximal effect at 23 μM) in hepatocytes incubated in the presence of 1.2 mM Ca2+ or 6 μM Ca2+; (b) taurolithocholate is able to activate the Ca2+‐dependent glycogen phosphorylase a by 6.3‐fold and 6.0‐fold in high and low Ca2+ media, respectively; (c) [14C]taurolithocholate influx is not affected by external Ca2+, and 45Ca2+ influx is not altered by taurolithocholate. These results establish that the effects of taurolithocholate on cell Ca2+ do not require extracellular Ca2+ and are consistent with the view that monohydroxy bile acids primarily release Ca2+ from the endoplasmic reticulum in the liver. Copyright © 1990, Wiley Blackwell. All rights reserved