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Biophys J. 2013 Jan 8;104(1):85-95. doi: 10.1016/j.bpj.2012.11.3818. Epub 2013 Jan 8.

Human AQP1 is a constitutively open channel that closes by a membrane-tension-mediated mechanism.

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1
Laboratorio de Biomembranas, Departamento de Ciencias Fisiológicas, Facultad de Medicina, Universidad de Buenos Aires, Buenos Aires, Argentina. mozu@fmed.uba.ar

Abstract

This work presents experimental results combined with model-dependent predictions regarding the osmotic-permeability regulation of human aquaporin 1 (hAQP1) expressed in Xenopus oocyte membranes. Membrane elastic properties were studied under fully controlled conditions to obtain a function that relates internal volume and pressure. This function was used to design a model in which osmotic permeability could be studied as a pressure-dependent variable. The model states that hAQP1 closes with membrane-tension increments. It is important to emphasize that the only parameter of the model is the initial osmotic permeability coefficient, which was obtained by model-dependent fitting. The model was contrasted with experimental records from emptied-out Xenopus laevis oocytes expressing hAQP1. Simulated results reproduce and predict volume changes in high-water-permeability membranes under hypoosmotic gradients of different magnitude, as well as under consecutive hypo- and hyperosmotic conditions. In all cases, the simulated permeability coefficients are similar to experimental values. Predicted pressure, volume, and permeability changes indicate that hAQP1 water channels can transit from a high-water-permeability state to a closed state. This behavior is reversible and occurs in a cooperative manner among monomers. We conclude that hAQP1 is a constitutively open channel that closes mediated by membrane-tension increments.

PMID:
23332061
PMCID:
PMC3540253
DOI:
10.1016/j.bpj.2012.11.3818
[Indexed for MEDLINE]
Free PMC Article
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