Cystic Fibrosis

[xjacob]

Does anyone know the basics of the mechanism for CF?
I know that with CF, you have a mutation in the CFTR channel, i.e. the one that is responsible for secretion of Cl in glands. Thus you don't secrete Na either, no water goes into the lumen and secretions are viscous. But I really don't see why would your sweat be "salty," i.e. high in NaCl. Aren't sweat glands just another type of exocrine glands? Am I missing something (well, obviously I must be...). Thanks in advance for any help.

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[chintu]

I think you've got the right idea but wrong mechanism. Look at Robbins figure pg491: With CFTR mutation in sweat glands you have decreased reabsorption of Cl- and Na+ so you have salty sweat. In the airway you have a decreased secretion and an increased reaborption of Na+ which leads to increased reabsorption of water so you have a dry inspissated mucus secretion.

 

[stochastic]

chintu is exactly right

I have always thought of it as if God just took the CFTR in the apical membrane of airway and pancreatic secretory cells and spun it 180 degrees when it was put in the sweat glands.

 

[xjacob]

Thanks a lot!!
The Robbins picture was a real help, too. I still think it is really unlikely for a channel to be flipped in one tissue vs. another (Robbins doesn't seem to mention anything in that sense, he just mentions the "net" function of CFTR) and I vaguely recall recall something about another Cl channel that interacts w/ CFTR. Or maybe the channel simply conduct both ways, and it's only the Cl gradient that determines the current. However, I think I will look that up AFTER the boards. In the meantime, the flipped channel model works PERFECT for me. THANKS!!