Abstract
BackgroundThe identification of strategies to improve mutant CFTR function remains a key priority in the development of new treatments for cystic fibrosis (CF). Previous studies demonstrated that the K+ channel opener 1-ethyl-2-benzimidazolone (1-EBIO) potentiates CFTR-mediated Cl− secretion in cultured cells and mouse colon. However, the effects of 1-EBIO on wild-type and mutant CFTR function in native human colonic tissues remain unknown.MethodsWe studied the effects of 1-EBIO on CFTR-mediated Cl− secretion in rectal biopsies from 47 CF patients carrying a wide spectrum of CFTR mutations and 57 age-matched controls. Rectal tissues were mounted in perfused micro-Ussing chambers and the effects of 1-EBIO were compared in control tissues, CF tissues expressing residual CFTR function and CF tissues with no detectable Cl− secretion.ResultsStudies in control tissues demonstrate that 1-EBIO activated CFTR-mediated Cl− secretion in the absence of cAMP-mediated stimulation and potentiated cAMP-induced Cl− secretion by 39.2±6.7% (P<0.001) via activation of basolateral Ca2+-activated and clotrimazole-sensitive KCNN4 K+ channels. In CF specimens, 1-EBIO potentiated cAMP-induced Cl− secretion in tissues with residual CFTR function by 44.4±11.5% (P<0.001), but had no effect on tissues lacking CFTR-mediated Cl−conductance.ConclusionsWe conclude that 1-EBIO potentiates Cl−secretion in native CF tissues expressing CFTR mutants with residual Cl− channel function by activation of basolateral KCNN4 K+ channels that increase the driving force for luminal Cl− exit. This mechanism may augment effects of CFTR correctors and potentiators that increase the number and/or activity of mutant CFTR channels at the cell surface and suggests KCNN4 as a therapeutic target for CF.
Highlights
The early onset multiorgan disease cystic fibrosis (CF) is caused by more than 1,800 mutations in the CFTR gene and remains the most common fatal monogenetic disease in Caucasian populations [1,2]
The CFTR gene encodes a cAMP-regulated Cl2 channel that localizes to the luminal membrane of epithelial cells, where it plays an important role in transepithelial ion and fluid transport
The notion that 1EBIO acted as a CFTR Cl2 channel opener in the absence of cAMP-mediated activation was supported by the observations i) that 1-EBIO-induced Cl2 secretory responses were inhibited by the CFTR inhibitor CFTRinh-172, and ii) that 1-EBIO failed to induce Cl2 secretion in rectal epithelia from CF patients carrying
Summary
We studied the effects of 1-EBIO on CFTR-mediated Cl2 secretion in rectal biopsies from 47 CF patients carrying a wide spectrum of CFTR mutations and 57 age-matched controls. Rectal tissues were mounted in perfused micro-Ussing chambers and the effects of 1-EBIO were compared in control tissues, CF tissues expressing residual CFTR function and CF tissues with no detectable Cl2 secretion
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