ROLE OF AQUAPORIN WATER CHANNELS IN BILE SECRETION

Abstract
Water is the major component of biological fluids. However, the molecular mechanisms underlying its transport through the cellular membranes remained unclear until the first water-selective protein channel was identified. These channels, named aquaporins (AQP), conform a family of integral membrane proteins broadly distributed among living organisms and facilitate the water movement across biological membranes. Hepatocytes, the cells that form the canalicular bile secretion, express three members of the AQP family: AQP0, AQP8 y AQP9. AQP 0 and 9 are constitutively localized in intracellular vesicles and basolateral membranes, respectively. On the other hand, AQP8 is predominantly located in intracellular vesicles but redistributes to the canalicular membrane upon stimulation with the hormone glucagon or its second messenger, cAMP. This redistribution leads to an increased hepatocyte membrane water permeability and induces bile secretion, suggesting a central role of AQP in bile formation. Hepatocyte AQP8 expression was found to be downregulated in the experimental model of extrahepatic obstructive cholestasis, suggesting that AQP are also involved in the mechanisms of bile secretory dysfunction.

Key words
Aquaporins, bile secretion, vesicle trafficking, water transport, glucagon

Bibliografía del artículo

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