Regulation of taurocholate and ursodeoxycholate uptake in hamster hepatocytes by Ca(2+)-mobilizing agents.
In isolated hamster hepatocytes, the Ca2+ ionophore A-23187 immediately decreased the uptake rate of taurocholic acid (TCA) by 60-70%, whereas it slowly inhibited that of ursodeoxycholic acid (UDCA) by a maximum of 35-45%, with an inhibition constant (Ki) of 0.36 and 1.93 microM, respectively. In contrast to ionomycin, which mimicked the effect of A-23187, vasopressin inhibited the bile acid uptake rate by 40 and 45%, respectively, only after a 5- to 10-min preincubation. The Na(+)-dependent bile acid transport was exclusively inhibited by these agents, and this inhibition was independent of extracellular Ca2+. However, intracellular Ca2+ depletion with ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid or chelation with 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid resulted in 40-50% inhibition of the uptake rate of both bile acids. The exogenous protein kinase C activator, phorbol 12-myristate 13-acetate (PMA), but not the nonactive 4 alpha-phorbol, significantly inhibited TCA uptake rate. Although both A-23187 and ionomycin immediately increased and decreased the cellular Na+ and K+ concentration, respectively, neither vasopressin nor PMA had a significant effect on the cellular concentration of these cations, even after a 10-min incubation. Furthermore, the effect of A-23187 and ionomycin on TCA uptake and Na+ flux, respectively, disappeared after a 40-min preincubation, and additional ionophore remained without effect. However, after a 40-min incubation with A-23187, PMA was still able to inhibit TCA uptake. Therefore, A-23187 and ionomycin transiently inhibited Na(+)-dependent uptake of both TCA and UDCA, in part because of transient alteration of the cellular Na+ and K+ concentration. Vasopressin and PMA inhibited Na(+)-dependent bile acid uptake, at least in part, through protein kinase C activation.
Bouscarel
B
B
Department of Medicine, George Washington University Medical Center, Washington, District of Columbia 20037, USA.
Reza
S
S
Dougherty
L A
LA
Fromm
H
H
Nussbaum
R
R
D000818:Animals; D000001:Calcimycin / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D006224:Cricetinae; D003840:Deoxycholic Acid / Q000378:metabolism*; D015759:Ionomycin / Q000494:pharmacology; D007476:Ionophores / Q000494:pharmacology*; D008099:Liver / Q000378:metabolism*; D008647:Mesocricetus; D012964:Sodium / Q000378:metabolism; D013656:Taurocholic Acid / Q000378:metabolism*; D014667:Vasopressins / Q000494:pharmacology
D007476:Ionophores; D003840:Deoxycholic Acid; D014667:Vasopressins; D000001:Calcimycin; D015759:Ionomycin; D013656:Taurocholic Acid; D012964:Sodium; D002118:Calcium