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CFTR
| Question | Answer |
|---|---|
| Verkman & Galietta 2009 | Review: Absence of specific blockers has hampered research. High throughput is producing some channel modulators and inhibitors (generally drugs for other uses). CaCC (TMEM16A) inhibitors were promising but fell through, only recently identified TMEM16A |
| Barrett & Keely 2000 | Review: Nutrient transporters tend to be obligate water conductors. Paracellin is involved in cation selectivity of paracellular transport. Adenosine activates CFTR through cAMP, neutrophils release adenosine precursor in some diseases. |
| Zhang et al 2010 | CFTR activated by small amounts of stretch, 61% of cells responded to stretch. PKA and PKC blockers had no effect, indicating there isnt a 2nd messenger system. Effects still see in Ca free soln. Current also seen in tissue, blockable with CFTR inhibitor |
| Simon et al 1999 | Shows paracellin is important in selectivity of paracellular cation transport. May be a channel. Mutations cause Mg2+ wasting |
| George et al 2009 | Review: treatment. Nebulised antibiotics, mannitol. Biofilms are the danger, grow slowly but can be 1000x more resistant. CF sputum can contain 10+ P.aeru colonies each with different resistance. Benzamil is an ENaC blocker potentiating aminoglycosides |
| Famesol | Quorum sensing molecule w possible use as a trojan horse, may be a particular vulnerability of biofilms. |
| Clarke & Harline 1996 | Shows cAMP regulates chloride secretion as well as absorption of both sodium and chloride. Also found that CFTR was responsible for most if not all effects of cAMP on Na/Cl homeostasis |
| Egan et al 1992 | Possible regulation of outward rectifier Cl channels (ORCC) by CFTR. CFTR reintroduced to rescue defective outward rectification, had these effects in addition to the obvious effects of adding CFTR channels |
| Boucher et al 1986 | CF airways have abnormally high sodium reabsorption. Beta agonists stim cAMP and cause increased Cl secretion in normal airways, in CF they simply increase Na absorption (reducing ASL). Used short cicuit current, isolated Na contribution using amiloride |
| Stutts et al 1995 | Cells expressing ENaC without CFTR showed increased sodium absorption in response to forskolin. By contrast, addition of CFTR prevented this increase, causing a decrease instead. May be due to ATP release through CFTR (similar to ORCC regulation) |
| Kunzelmann et al 1997 | Shows direct protein-protein interaction between CFTR and ENaC. Intracellular CFTR fragment containing NBD1 and R domain was sufficient to restore regulation. Colocalisation may be to increase ATP concn at ENaC or simple direct action through protein link |
| Fulmer et al 1995 | Showed that of two intracellular mutation both allowed Cl conductance but the more severe disease was linked with an inability to regulate ORCC. Same mutation that failed ENaC regulation in Kunzelman 97, role in ATP extrusion or attachment to scaffold? |
| Schweibert et al 1995 | Same group as Fulmer. Trapping of extracellular ATP by hexokinase prevented the CFTR-ORCC interaction. Study also shows conclusively that CFTR causes ATP efflux. |
| Bradbury 1999 (only author) | Review: Discusses a possible role for CFTR in vesicle trafficking, may be that CFTR acts as an intracellular channel protein before reaching the membrane. Important as mucus is excreted by exocytosis. |
| Lu et al 2006 | CFTR interacts with ROMK, mediating response to intracell ATP and glibenclamide. Reqd for glibenclamide block of ROMK, like SUR proteins. Interaction may be via a scaffolidng protein. Glibenclamide strange as it has previously been used to block CFTR |
| Loussouarn et al 1996 | Shows that cells transfected with CFTR gain a cAMP stimulated K+ current which may be ROMK. Used whole cell patch clamping. Interferon also reduces the K+ current in line with CFTR gene reduction. |
| Mall et al 2004 | Transgenic mice with increased Na absorption (by increased ENaC) show reduced survival, due to mucus plugs rather than infection foci. Better mouse model than CFTR dysfunction |
| Garcia et al 2009 | HCO3 secretion is required for mucin secretion, basal levels the same but on PGE/5HT stimulation HCO3 free preps produced less. Adding luminal HCO3 didnt help. No ENaC dependent sodium absorption in the biliary tree (so these symptoms must be CFTR). |
| Sugita et al 1998 | Evidence suggesting ATP is extruded by a closely associated but separate pore which relies on CFTR entirely. Found multiple Cl channels associated with 1 or 2 ATP channels, if same protein numbers would be equal. Channels were pharmacologically distinct. |
| Poulsen et al 1994 | CFTR also conducts HCO3. Forskolin dependent pH change didnt occur in HCO3-free + CO2-free solution. HCO3 permeability 1/4 of Cl-. pH will be lower in CF epithelial lumen. F508 mutants have poor HCO3 conductance. |
| Caputo et al 2008 | Identifies the CaCC channel as TMEM16A. IL4 was known to regulate CaCC so they looked for genes regulated by IL4. siRNA screen of putative targets to disrupt CaCC. Exploited halide sensitivity of YFP to assay I- influx. |
| Murek et al 2010 | Review: Covers intestinal chloride secretion although criticised by Lucas 2010 for taking too much of the in vitro data for granted and relying heavily on short-circuit currents |
| Gyomorey et al 2000 | ClC2 protein appears to be present in intestine, CFTR KO mice show a conductance that exhibits the properties expected for ClC. Uses Ussing chambers and short-circuit currents. Odd distribution, close to tight junctions. |
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Jonmassie
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