Cyclic AMP and cell swelling stimulate hepatic Na ؉ /TC cotransport and Ntcp translocation via the phosphoinositide 3-kinase signaling pathway. To determine the downstream target of the phosphoinositide 3-kinase action, we examined the role of protein kinase B (PKB)/Akt using SB203580 in hepatocytes as well as by transfection with a dominant negative (DN-PKB) or a constitutively active (CA-PKB) form of PKB in HuH-Ntcp cells. Both cAMP and cell swelling stimulated p38 mitogen-activated protein

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... AP) kinase as well as PKB activity. Although 100 M SB203580 inhibited cell swelling-and 8-chlorophenylthio-cAMP-induced activation of both p38 MAP kinase and PKB, 1 M SB203580 inhibited activation of p38 MAP kinase, but not of PKB, in hepatocytes. 100 M, but not 1 M SB203580, inhibited cell swelling-and cAMP-induced increases in taurocholate (TC) uptake and Ntcp translocation in hepatocytes. TC uptake in HuH-Ntcp cells was more than 90% dependent on extracellular Na ؉ . Cyclic AMP and cell swelling increased TC uptake by 50 -100% and PKB activity 2-4-fold in HuH-Ntcp cells transfected with the empty vector and failed to increase PKB activity, TC uptake, and Ntcp translocation in DN-PKB-transfected HuH-Ntcp cells. Transfection with CA-PKB increased PKB activity, TC uptake, and Ntcp translocation in HuH-Ntcp cells compared with cells transfected with the empty vector. In contrast, transfection with DN-PKB did not affect basal PKB activity, TC uptake, or Ntcp translocation. Taken together, these results strongly suggest that cell swelling and cAMP-mediated stimulation of hepatic Na ؉ /TC cotransport and Ntcp translocation requires activation of PKB and is mediated at least in part via a phosphoinositide 3-kinase/PKB-signaling pathway.