Development of Automated Patch Clamp Technique to Investigate CFTR Chloride Channel Function

International audienceThe chloride (Cl-) channel cystic fibrosis transmembrane conductance regulator (CFTR) is defective in cystic fibrosis (CF), and mutation of its encoding gene leads to various defects such as retention of the misfolded protein in the endoplasmic reticulum, reduced stability at the plasma membrane, abnormal channel gating with low open probability, and thermal instability, which leads to inactivation of the channel at physiological temperature. Pharmacotherapy is one major therapeutic approach in the CF field and needs sensible and fast tools to identify promising compounds. The high throughput screening assays available are often fast and sensible techniques but with lack of specificity. Few works used automated patch clamp (APC) for CFTR recording, and none have compared conventional and planar techniques and demonstrated their capabilities for different types of experiments. In this study, we evaluated the use of planar parallel APC technique for pharmacological search of CFTR-trafficking correctors and CFTR function modulators. Using optimized conditions, we recorded both wt- and corrected F508del-CFTR Cl- currents with automated whole-cell patch clamp and compared the data to results obtained with conventional manual whole-cell patch clamp. We found no significant difference in patch clamp parameters such as cell capacitance and series resistance between automated and manual patch clamp. Also, the results showed good similarities of CFTR currents recording between the two methods. We showed that similar stimulation protocols could be used in both manual and automatic techniques allowing precise control of temperature, classic I/V relationship, and monitoring of current stability in time. In conclusion, parallel patch-clamp recording allows rapid and efficient investigation of CFTR currents with a variety of tests available and could be considered as new tool for medium throughput screening in CF pharmacotherapy

Expression and function of cystic fibrosis transmembrane conductance regulator in rat intrapulmonary arteries.

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Benzo(c)quinolizinium drugs inhibit degradation of Delta F508-CFTR cytoplasmic domain

Proteins comprising the first nucleotide-binding- and R-domains of wild-type and ?F508 cystic fibrosis transmembrane conductance regulator (CFTR) have been synthesised by in vitro transcription/translation. The kinetics and extent of degradation of wild-type and ?F508 cytoplasmic domain proteins in rabbit reticulocyte lysates, in which proteasome activity was inhibited, were similar, with a half-life of approximately 4 h. The results show for the first time, that the benzo(c)quinolizinium compounds, MPB-07 and MPB-91, selectively inhibit degradation of the ?F508 cytoplasmic domain protein. Studies using protease inhibitors demonstrated that both ?F508 and wild-type proteins are substrates for cysteine proteases. The studies provide evidence that benzo(c)quinolizinium compounds protect a proteolytic cleavage site by direct binding to the first cytoplasmic domain of ?F508-CFTR and this is a likely mechanism for increasing ?F508-CFTR trafficking in intact cells

Rescue of functional delF508-CFTR channels in cystic fibrosis epithelial cells by the alpha-glucosidase inhibitor miglustat.

In the disease cystic fibrosis (CF), the most common mutation delF508 results in endoplasmic reticulum retention of misfolded CF gene proteins (CFTR). We show that the alpha-1,2-glucosidase inhibitor miglustat (N-butyldeoxynojirimycin, NB-DNJ) prevents delF508-CFTR/calnexin interaction and restores cAMP-activated chloride current in epithelial CF cells. Moreover, miglustat rescues a mature and functional delF508-CFTR in the intestinal crypts of ileal mucosa from delF508 mice. Since miglustat is an orally active orphan drug (Zavesca) prescribed for the treatment of Gaucher disease, our findings provide the basis for future clinical evaluation of miglustat in CF patients