INVESTIGADORES
LAROCCA Maria Cecilia
artículos
Título:
Glucagon induces the plasma membrane insertion of functional aquaporin-8 water channels in isolated rat hepatocytes
Autor/es:
GRADILONE, S.A.; GARCIA, F; HUEBERT, R.C.; TIETZ, P.S.; LAROCCA, M.C.; KIERBEL, A.; CARRERAS, F.I.; LARUSSO, N.F.; MARINELLI, R.A.
Revista:
HEPATOLOGY (BALTIMORE, MD.)
Editorial:
AASLD
Referencias:
Año: 2003 vol. 37 p. 1435 - 1441
ISSN:
0270-9139
Resumen:
Although glucagon is known to stimulate the cyclic adenosine monophosphate (cAMP)-mediated
hepatocyte bile secretion, the precise mechanisms accounting for this choleretic effect are
unknown.Werecently reported that hepatocytes express the water channel aquaporin-8 (AQP8),
which is located primarily in intracellular vesicles, and its relocalization to plasma membranes
can be induced with dibutyryl cAMP. In this study, we tested the hypothesis that glucagon
induces the trafficking of AQP8 to the hepatocyte plasma membrane and thus increases membrane
water permeability. Immunoblotting analysis in subcellular fractions from isolated rat
hepatocytes indicated that glucagon caused a significant, dose-dependent increase in the amount
of AQP8 in plasma membranes (e.g., 102% with 1 mol/L glucagon) and a simultaneous
decrease in intracellular membranes (e.g., 38% with 1mol/L glucagon). Confocal immunofluorescence
microscopy in cultured hepatocytes confirmed the glucagon-induced redistribution of
AQP8 from intracellular vesicles to plasma membrane. Polarized hepatocyte couplets showed
that this redistribution was specifically to the canalicular domain. Glucagon also significantly
increased hepatocyte membrane water permeability by about 70%, which was inhibited by the
water channel blocker dimethyl sulfoxide (DMSO). The inhibitors of protein kinase A, H-89, and
PKI, as well as the microtubule blocker colchicine, prevented the glucagon effect on both AQP8
redistribution to hepatocyte surface and cell membrane water permeability. In conclusion, our data
suggest that glucagon induces the protein kinase A and microtubule-dependent translocation of
AQP8 water channels to the hepatocyte canalicular plasma membrane, which in turn leads to an
increase in membrane water permeability. These findings provide evidence supporting the molecular
mechanisms of glucagon-induced hepatocyte bile secretion. (HEPATOLOGY 2003;37:1435-1441.)(HEPATOLOGY 2003;37:1435-1441.)
e.g., 38% with 1
e.g., 102% with 1 mol/L glucagon) and a simultaneous
decrease in intracellular membranes (e.g., 38% with 1mol/L glucagon). Confocal immunofluorescence
microscopy in cultured hepatocytes confirmed the glucagon-induced redistribution of
AQP8 from intracellular vesicles to plasma membrane. Polarized hepatocyte couplets showed
that this redistribution was specifically to the canalicular domain. Glucagon also significantly
increased hepatocyte membrane water permeability by about 70%, which was inhibited by the
water channel blocker dimethyl sulfoxide (DMSO). The inhibitors of protein kinase A, H-89, and
PKI, as well as the microtubule blocker colchicine, prevented the glucagon effect on both AQP8
redistribution to hepatocyte surface and cell membrane water permeability. In conclusion, our data
suggest that glucagon induces the protein kinase A and microtubule-dependent translocation of
AQP8 water channels to the hepatocyte canalicular plasma membrane, which in turn leads to an
increase in membrane water permeability. These findings provide evidence supporting the molecular
mechanisms of glucagon-induced hepatocyte bile secretion. (HEPATOLOGY 2003;37:1435-1441.)(HEPATOLOGY 2003;37:1435-1441.)
e.g., 38% with 1mol/L glucagon). Confocal immunofluorescence
microscopy in cultured hepatocytes confirmed the glucagon-induced redistribution of
AQP8 from intracellular vesicles to plasma membrane. Polarized hepatocyte couplets showed
that this redistribution was specifically to the canalicular domain. Glucagon also significantly
increased hepatocyte membrane water permeability by about 70%, which was inhibited by the
water channel blocker dimethyl sulfoxide (DMSO). The inhibitors of protein kinase A, H-89, and
PKI, as well as the microtubule blocker colchicine, prevented the glucagon effect on both AQP8
redistribution to hepatocyte surface and cell membrane water permeability. In conclusion, our data
suggest that glucagon induces the protein kinase A and microtubule-dependent translocation of
AQP8 water channels to the hepatocyte canalicular plasma membrane, which in turn leads to an
increase in membrane water permeability. These findings provide evidence supporting the molecular
mechanisms of glucagon-induced hepatocyte bile secretion. (HEPATOLOGY 2003;37:1435-1441.)(HEPATOLOGY 2003;37:1435-1441.)