CFTR is an essential mediator of salt and water transport across lung and gut epithelia. Defects in the synthesis or regulation of this chloride channel cause several human disorders including cystic fibrosis (CF), male infertility and diarrhea. The development of drugs to treat these CFTR-related disorders is at an early stage. The most common CF mutant is deltaF508-CFTR, which is inefficiently delivered to the cell surface. This mutant may also exhibit defective channel gating when it reaches the cell surface, but the extent of this defect and the underlying mechanisms are unknown. We have identified a new class of CFTR channel opener that potently activates wild type and deltaF508-CFTR channels. Our identification of these compounds was based on our discovery that a commonly used blocker of the CFTR pore behaves as a mixed agonist toward channels that have low activity (e.g., poorly phosphorylated or oxidized channels). Based on this observation, we identified a derivative of this pore blocker that behaves as a pure CFTR agonist. This compound potently (EC50 < 1 mu/M) and specifically stimulates CFTR channel opening in excised membrane patches and CFTR-mediated chloride currents in intact epithelial monolayers. This opener dramatically stimulates the activities of membrane-resident deltaF508-CFTR channels under conditions when the wild type channel is nearly fully active; thus, the deltaF508 mutation appears to substantially disrupt channel gating. We propose 3 specific aims: (1) to define the mechanism by which these compounds stimulate CFTR channel opening; (2) to determine the extent to which the deltaF508 mutation affects CFTR channel gating and the underlying mechanism for this inhibitory effect; and (3) to exploit the chemistry of these compounds to develop more potent CFTR channel openers and identify naturally occurring CFTR agonists. The results of this project should help clarify the normal mechanisms that control CFTR gating, define the effect of the most common CF mutation on CFTR gating, and possibly lead to the development of new CF drugs.
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