Ursodeoxycholate mobilizes intracellular Ca2+ and activates phosphorylase a in isolated hepatocytes.
In isolated hamster hepatocytes, ursodeoxycholic acid (UDCA) mobilized intracellular free calcium ([Ca2+]i) and activated phosphorylase a with a half-maximally effective concentration of 188 and 9 microM, respectively. Addition of ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA) did not affect the maximum [Ca2+]i mobilized by UDCA; however, [Ca2+]i returned to basal levels in 4-5 min compared with > 10 min in the absence of EGTA. Both UDCA and vasopressin activated phosphorylase a to the same extent in the presence and absence of extracellular Ca2+, and the effect of both agents was abolished when the cells were depleted in Ca2+. Vasopressin (100 nM) did not further mobilize [Ca2+]i or activate phosphorylase a when combined with 500 microM UDCA. However, unlike vasopressin, UDCA did not stimulate inositol 1,4,5-trisphosphate (IP3) formation. In contrast to taurine-conjugated UDCA (TUDCA), concentration < or = 500 microM of glycine-conjugated UDCA (GUDCA) did not affect either [Ca2+]i or phosphorylase a. Lithocholic acid and taurolithocholic acid (TLCA) displayed the highest affinity for Ca2+. In addition, TLCA, chenodeoxycholic acid, and NaF stimulated Ca2+ efflux at concentrations as low as 100 microM, 200 microM, and 5 mM, respectively. Conversely, UDCA, TUDCA, and GUDCA presented the lowest affinity for Ca2+ and had no effect on Ca2+ efflux. The 28% increase in Ca2+ release induced by TLCA alone was further augmented to approximately 60% when TLCA was combined with UDCA, TUDCA, or GUDCA. However, Ca2+ efflux induced by NaF was not further increased by UDCA and its conjugates.(ABSTRACT TRUNCATED AT 250 WORDS)
Bouscarel
B
B
Department of Medicine, George Washington University Medical Center, Washington, District of Columbia 20037.
Fromm
H
H
Nussbaum
R
R
D000634:Aminoquinolines; D000818:Animals; D001647:Bile Acids and Salts / Q000378:metabolism / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002469:Cell Separation; D002614:Chelating Agents; D006224:Cricetinae; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation / Q000187:drug effects; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D007425:Intracellular Membranes / Q000378:metabolism*; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D008099:Liver / Q000166:cytology / Q000378:metabolism*; D008297:Male; D010762:Phosphorylase a / Q000378:metabolism*; D006005:Phosphorylases / Q000378:metabolism; D014580:Ursodeoxycholic Acid / Q000494:pharmacology*; D014667:Vasopressins / Q000494:pharmacology
D000634:Aminoquinolines; D001647:Bile Acids and Salts; D002614:Chelating Agents; D014667:Vasopressins; D014580:Ursodeoxycholic Acid; C035738:Quin2-acetoxymethyl ester; D015544:Inositol 1,4,5-Trisphosphate; D007770:L-Lactate Dehydrogenase; D010762:Phosphorylase a; D006005:Phosphorylases; D002118:Calcium