CFTR Protein...

[BlackNDecker]

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I am having trouble conceptualizing the sweat test. Respiratory and Digestive problems are because the CFTR(CFTCR whichever way you learned it) doesn't pump Cl- out with the associated H2O, resulting in thick mucus secretions. However, the problem with the sweat is that the Cl- can't be absorbed? Is this because the CFTR channel is reversed in epithelial cells? Is it because the the pump shuttles Cl- both directions?

Also, Na+ is excreted in the respiratory/pancreatic secretions for electric neutrality...So is it the Na+ that carries the H2O for hydration of the mucus? Or is the Cl- as important for H2O transfer as the Na+?

Thanks...

 

[BlackNDecker]

When we sweat, ions(Cl, Na, K) are absorbed into the basilar portion of the sweat gland. The composition of the sweat is then adjusted in the ductal portion of the sweat gland before being secreted onto the surface of the skin.

At slow flow rates(light sweating), alternative modes of Cl- transfer are operating(natural leakiness of the membrane, other Cl channels, etc.)....so the Cl and the Na(for electrical neutrality) along with the water (for Osmotic equilibrium) are adjusted appropriately within the ductal cells of the sweat gland before the secretion ends up on the skin.

But at High flow rates, the rate of flow is too much for the alternative transport processes to compensate for the lack of CFTR function, and the sweat composition can't be adjusted...Cl, Na, etc. end up on the epithelial surface.

Sound right? Feel free to critique, correct, ridicule, etc....