by Eva K. Roth, Stephanie Hirtz, Julia Duerr, Daniel Wenning, Irmgard Eichler, Hans H. Seydewitz, Margarida D. Amaral, Marcus A. Mall
The 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. Methods
We 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. Results
Studies 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. Conclusions
We 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.