Induction of cholestasis in the perfused rat liver by 2-aminoethyl diphenylborate, an inhibitor of the hepatocyte plasma membrane Ca2+ channels.
OBJECTIVE
An increase in the cytoplasmic free Ca2+ concentration in hepatocytes as a result of the release of Ca2+ from intracellular stores and Ca2+ inflow from the extracellular space is a necessary part of the mechanism by which bile acids are moved along the bile cannaliculus by contraction of the cannaliculus. 2-Aminoethyl diphenylborate (2-APB) is a recently discovered inhibitor of store-operated plasma membrane Ca2+ channels in hepatocytes. The aim of the present study was to test the ability of 2-APB to inhibit bile flow.


METHODS
Bile flow was measured in the isolated perfused rat liver using cannulation of the common bile duct. Measurements were carried out in the presence or absence of 2-APB in either the presence of taurocholic acid (to enhance basal bile flow) or in the absence of taurocholic acid and in the presence of the hormones vasopressin and glucagon, which are known to stimulate bile flow.


RESULTS
In livers perfused in the presence of taurocholic acid, 2-APB reversibly inhibited bile flow with a slow time of onset. The time of onset of inhibition was reduced by prior addition of the endoplasmic reticulum (Ca(2+) + Mg2+)adenosine triphosphatase inhibitor, 2,5-di-t-butylhydroquinone. In livers perfused in the absence of taurocholate, 2-APB had little effect on the basal rate of bile flow, but inhibited the ability of vasopressin and glucagon to stimulate bile flow.


CONCLUSIONS
It is concluded that an inhibitor of hepatocyte plasma membrane Ca2+ channels can induce cholestasis. The results provide evidence that suggests that, over a period of time, the normal function of hepatocyte store-operated Ca2+ channels is required to maintain bile flow. Future strategies directed at the regulation of bile flow might include pharmacological or other interventions that modulate Ca2+ inflow to hepatocytes.
Gregory
Roland B
RB
Department of Medical Biochemistry, School of Medicine, Faculty of Health Sciences, Flinders University, Adelaide, South Australia, Australia.
Hughes
Rachael
R
Barritt
Gregory J
GJ
D000818:Animals; D001646:Bile / Q000187:drug effects* / Q000502:physiology; D001896:Boron Compounds / Q000009:adverse effects*; D002121:Calcium Channel Blockers / Q000009:adverse effects*; D015220:Calcium Channels / Q000187:drug effects; D000252:Calcium-Transporting ATPases / Q000187:drug effects; D002779:Cholestasis / Q000139:chemically induced* / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005934:Glucagon / Q000494:pharmacology; D022781:Hepatocytes / Q000378:metabolism*; D006873:Hydroquinones / Q000494:pharmacology; D008099:Liver / Q000378:metabolism; D036361:Peptide Hormones / Q000494:pharmacology; D051381:Rats; D013656:Taurocholic Acid / Q000494:pharmacology; D014667:Vasopressins / Q000494:pharmacology
D001896:Boron Compounds; D002121:Calcium Channel Blockers; D015220:Calcium Channels; D004791:Enzyme Inhibitors; D006873:Hydroquinones; D036361:Peptide Hormones; D014667:Vasopressins; C019359:2,5-di-tert-butylhydroquinone; D013656:Taurocholic Acid; D005934:Glucagon; C109986:2-aminoethoxydiphenyl borate; D000252:Calcium-Transporting ATPases