Gastrin inhibits cholangiocyte growth in bile duct-ligated rats by interaction with cholecystokinin-B/gastrin receptors via D-myo-inositol 1,4,5-triphosphate-, Ca2+-, and protein kinase C alpha-dependent mechanisms

We studied the role of gastrin in regulating cholangiocyte proliferation in duced by bile duct ligation (BDL), In purified cholangiocytes, we evaluated (1) for the presence of cholecystokinin-B (CCK-B)/gastrin receptors, (2) t he effect of gastrin on D-myo-Inositol 1,4,5-triphosphate (IP3) levels, and (3) the effect of gastrin on DNA synthesis and adenosine 3',5'-monophospha te (cAMP) levels in the absence or presence of CCK-A (L-364,718) and CCK-B/ gastrin (L-365,260) receptor inhibitors, 1,2-bis (2-aminophenoxy)ethane-N,N ,N',N'-tetraacetic acid tetrakis(acetxymethyl ester) (BAPTA/AM; an intracel lular Ca2+ chelator), and 2 protein kinase C (PKC) inhibitors, 1-(5-Isoquin olinylsulfonyl)-2-methylpiperazine (H7) and staurosporin, To evaluate if ga strin effects on cholangiocyte proliferation are mediated by the isoform PK C alpha, we evaluated (1) for the presence of PKC alpha in cholangiocytes a nd (2) the effect of gastrin on the PKC alpha protein expression in a trito n-soluble (containing cytoplasm + membrane) and a triton-insoluble (contain ing cytoskeleton) fraction. To evaluate the effects of gastrin in vivo, imm ediately following BDL, gastrin or bovine serum albumin (BSA) was infused b y minipumps for 7 days to rats and we measured cholangiocyte growth and cAM P levels. We found CCK-B/gastrin receptors on cholangiocytes. Gastrin incre ased IP3 levels. Gastrin inhibited DNA synthesis and cAMP synthesis in chol angiocytes. Gastrin effects on cholangiocyte functions were blocked by L-36 5,260, BAPTA/AM, 117, and staurosporin but not by L-364-718, Gastrin induce d translocation of PKC alpha from cholangiocyte cytoskeleton to membrane. I n vivo, gastrin decreased cholangiocyte growth and cAMP synthesis compared with controls. We concluded that gastrin inhibits cholangiocyte growth in B DL rats by interacting with CCK-B/gastrin receptors through a signal transd uction pathway involving IP3, Ca2+, and PKC alpha.