TRANSPORT OF SMALL MOLECULES ACROSS CELL MEMBRANES: WATER CHANNELS AND UREA TRANSPORTERS

2002 ◽  
Vol 26 (3) ◽  
pp. 146-157 ◽  
Author(s):  
Barbara E. Goodman

How do small hydrophilic nonelectrolytes cross cell membranes? Which pathways are most important for small lipid insoluble molecules to cross cell membranes? These are questions that have been basic to membrane transport physiology for decades. More importantly, these are questions whose answers have changed significantly within the last 10 years. This review discusses the evidence that pathways other than the lipid bilayer itself exist for the transport across cell membranes of specific small hydrophilic nonelectrolytes. The description begins with briefly analyzing the relevance of well accepted basic mathematical models for transport for understanding the permeability of representative physiologically important molecules across actual cell membranes. Particular emphasis is placed on describing recently discovered proteins that facilitate the transport of some of the smallest physiologically important lipid-insoluble molecules, water, and urea. Evidence also exists for transport proteins that selectively enhance the transmembrane transport of other small lipid-insoluble molecules. Do nonselective pores for small molecules exist in cell membranes?

1996 ◽  
Vol 270 (1) ◽  
pp. C12-C30 ◽  
Author(s):  
A. S. Verkman ◽  
A. N. van Hoek ◽  
T. Ma ◽  
A. Frigeri ◽  
W. R. Skach ◽  
...  

This review summarizes recent progress in water-transporting mechanisms across cell membranes. Modern biophysical concepts of water transport and new measurement strategies are evaluated. A family of water-transporting proteins (water channels, aquaporins) has been identified, consisting of small hydrophobic proteins expressed widely in epithelial and nonepithelial tissues. The functional properties, genetics, and cellular distributions of these proteins are summarized. The majority of molecular-level information about water-transporting mechanisms comes from studies on CHIP28, a 28-kDa glycoprotein that forms tetramers in membranes; each monomer contains six putative helical domains surrounding a central aqueous pathway and functions independently as a water-selective channel. Only mutations in the vasopressin-sensitive water channel have been shown to cause human disease (non-X-linked congenital nephrogenic diabetes insipidus); the physiological significance of other water channels remains unproven. One mercurial-insensitive water channel has been identified, which has the unique feature of multiple overlapping transcriptional units. Systems for expression of water channel proteins are described, including Xenopus oocytes, mammalian and insect cells, and bacteria. Further work should be directed at elucidation of the role of water channels in normal physiology and disease, molecular analysis of regulatory mechanisms, and water channel structure determination at atomic resolution.


1991 ◽  
Vol 6 (3) ◽  
pp. 233-237 ◽  
Author(s):  
Hans Kiefer ◽  
Barbara Klee ◽  
Edgar John ◽  
York-Dieter Stierhof ◽  
Fritz Jähnig

2013 ◽  
Vol 53 (supplement1-2) ◽  
pp. S248
Author(s):  
Naoki Soga ◽  
Rikiya Watanabe ◽  
Shinya Ohdate ◽  
Hiroyuki Noji

2017 ◽  
pp. 597-640 ◽  
Author(s):  
Bruce Alberts ◽  
Alexander Johnson ◽  
Julian Lewis ◽  
David Morgan ◽  
Martin Raff ◽  
...  

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