The effect of bile salts and calcium on isolated rat liver mitochondria

Intact mitochondria were incubated with and without calcium in solutions of chenodeoxycholate, ursodeoxycholate, or their conjugates. Glutamate dehydr ogenase, protein and phospholipid release were measured. Alterations in mem brane and organelle structure were investigated by electron paramagnetic re sonance spectroscopy. Chenodeoxycholate enhanced enzyme liberation, solubil ized protein and phospholipid, and increased protein spin label mobility an d the polarity of the hydrophobic membrane interior, whereas ursodeoxychola te and its conjugates did not damage mitochondria. Preincubation with ursod eoxycholate or its conjugate tauroursodeoxycholate for 20 min partially pre vented damage by chenodeoxycholate. Extended preincubation even with 1 mM u rsodeoxycholate could no longer prevent structural damage. Calcium (from 0. 01 mM upward) augmented the damaging effect of chenodeoxycholate (0.15-0.5 mM). The combined action of 0.01 mM calcium and 0.15 mM chenodeoxycholate w as reversed by ursodeoxycholate only, not by its conjugates tauroursodeoxyc holate and glycoursodeoxycholate. In conclusion, ursodeoxycholate partially prevents chenodeoxycholate-induced glutamate dehydrogenase release from li ver cell mitochondria by membrane stabilization. This holds for shorter tim es and at concentrations below 0.5 mM only, indicating that the different c onstitution of protein-rich mitochondrial membranes does not allow optimal stabilization such as has been seen in phospholipid- and cholesterol-rich h epatocyte cell membranes, investigated previously. (C) 1999 Elsevier Scienc e B.V. All rights reserved.