cAMP increases liver Na+-taurocholate cotransport by translocating transporter to plasma membranes

Am J Physiol. 1997 Oct;273(4):G842-8. doi: 10.1152/ajpgi.1997.273.4.G842.

Abstract

Adenosine 3',5'-cyclic monophosphate (cAMP), acting via protein kinase A, increases transport maximum of Na+-taurocholate cotransport within 15 min in hepatocytes (S. Grüne, L. R. Engelking, and M. S. Anwer. J. Biol. Chem. 268: 17734-17741, 1993); the mechanism of this short-term stimulation was investigated. Cycloheximide inhibited neither basal nor cAMP-induced increases in taurocholate uptake in rat hepatocytes, indicating that cAMP does not stimulate transporter synthesis. Studies in plasma membrane vesicles showed that taurocholate uptake was not stimulated by the catalytic subunit of protein kinase A but was higher when hepatocytes were pretreated with cAMP. Immunoblot studies with anti-fusion protein antibodies to the cloned Na+-taurocholate cotransport polypeptide (Ntcp) showed that pretreatment of hepatocytes with cAMP increased Ntcp content in plasma membranes but not in homogenates. Ntcp was detected in microsomes, endosomes, and Golgi fractions, and cAMP pretreatment resulted in a decrease only in endosomal Ntcp content. It is proposed that cAMP increases transport maximum of Na+-taurocholate cotransport, at least in part, by translocating Ntcp from endosomes to plasma membranes.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Biological Transport
  • Bucladesine / pharmacology
  • Carrier Proteins / metabolism*
  • Cell Membrane / metabolism
  • Cells, Cultured
  • Cyclic AMP / pharmacology*
  • Cyclic AMP-Dependent Protein Kinases / metabolism
  • Cycloheximide / pharmacology
  • Endosomes / metabolism
  • Kinetics
  • Liver / drug effects
  • Liver / metabolism*
  • Male
  • Microsomes, Liver / metabolism
  • Organic Anion Transporters, Sodium-Dependent*
  • Rats
  • Rats, Wistar
  • Subcellular Fractions / metabolism
  • Symporters*
  • Taurocholic Acid / metabolism

Substances

  • Carrier Proteins
  • Organic Anion Transporters, Sodium-Dependent
  • Symporters
  • sodium-bile acid cotransporter
  • Taurocholic Acid
  • Bucladesine
  • Cycloheximide
  • Cyclic AMP
  • Cyclic AMP-Dependent Protein Kinases