Objective:

The cystic fibrosis transmembrane conductance regulator (CFTR) is a Cl^- channel which is localized in the apical membrane of various epithelial cells. In pulmonary epithelial cells CFTR is exposed to different physical forces that are reasoned by breathing such as strain and shear force (SF). The present study questioned whether or not these stimuli affect CFTR-mediated currents in order to reveal if CFTR is a mechanosensitive ion channel.

Methods:

Activity of heterologously expressed human CFTR (hCFTR) was measured by the two-electrode-voltage-clamp technique. CFTR-mediated currents were elicited by application of 5 µM forskolin and 100 µM IBMX (F/I) and the F/I-induced current (I_F/I) was measured. Strain which results in distension of the oocyte membrane, was induced by injection of an intracellular analogous solution or osmotic swelling. SF (1.3 dyn/cm) was generated by a fluid stream.

Results:

In control experiments, CFTR was activated by two-time application of F/I. The second I_F/I was significantly reduced by 74±1% compared to the first I_F/I. Injection of 55.2 nl increased I_F/I by 170±4%. Increasing the injection volume to 110.4 nl and 147.2 nl further augmented the I_F/I up to 475±5%. Similar results were observed by hypotonic-induced cell swelling. In contrast, hypertonic cell shrinkage had no effect on I_F/I. With different experimental procedures no effect of SF on I_F/I was detected.

Conclusions:

These data indicate that CFTR-activity is increased by strain. Furthermore, SF is not the adequate stimulus for CFTR activation in Xenopus oocytes. Mechanosensitive gating of CFTR reveals new relevance for pulmonary epithelial physiology.