After Damage of Large Bile Ducts by Gamma-Aminobutyric Acid Small Ducts Replenish the Biliary Tree by Amplification of Calcium-Dependent Signaling and de Novo Acquisition of Large Cholangiocyte Phenotypes

摘要

Large cholangiocytes secrete bicarbonate in response to secretin and proliferate after bile duct ligation by activation of cyclic adenosine 3′, 5′-monophosphate signaling. The Ca²⁺-dependent adenylyl cyclase 8 (AC8, expressed by large cholangiocytes) regulates secretin-induced choleresis. Ca²⁺-dependent protein kinase C (PKC) regulates small cholangiocyte function. Because γ-aminobutyric acid (GABA) affects cell functions by activation of both Ca²⁺ signaling and inhibition of AC, we sought to develop an >in vivo model characterized by large cholangiocyte damage and proliferation of small ducts. Bile duct ligation rats were treated with GABA for one week, and we evaluated: GABAA, GABAB, and GABAC receptor expression; intrahepatic bile duct mass (IBDM) and the percentage of apoptotic cholangiocytes; secretin-stimulated choleresis; and extracellular signal-regulated kinase1/2 (ERK1/2) phosphorylation and activation of Ca^2+-dependent PKC isoforms and AC8 expression. We found that both small and large cholangiocytes expressed GABA receptors. GABA: (i) induced apoptosis of large cholangiocytes and reduced large IBDM; (ii) decreased secretin-stimulated choleresis; and (iii) reduced ERK1/2 phosphorylation and AC8 expression in large cholangiocytes. Small cholangiocytes: (i) proliferated leading to increased IBDM; (ii) displayed activation of PKCβII; and (iii) >de novo expressed secretin receptor, cystic fibrosis transmembrane regulator, Cl⁻/HCO3⁻ anion exchanger 2 and AC8, and responded to secretin. Therefore, in pathologies of large ducts, small ducts replenish the biliary epithelium by amplification of Ca²⁺-dependent signaling and acquisition of large cholangiocyte phenotypes.