Airway epithelial cells beating mutations of the cystic fibrosis (CF) transmembrane conductance regulator (CFTR) possess an increased Na ÷ conductance along with their well described defect of cAMP dependent CI-conductance. Currently it is not clear, how this occurs, and whether it is due to a CFTR control of epithelial Na ÷ conductances which might be defective in CF patients. In the present study, we have tried to identify possible interactions between both CFTR and the epithelial Na ÷ conductance by overexpressing respective cRNAs in Xenopus oocytes. The expression of aH three (~, [~, ~) subunits of the rat epithelial Na ÷ channel (rENaC) and wild type (wt) CFTR resulted in the expected amiloride sensitive Na ÷ and IBMX (1 mmol/l) activated CI-currents, respectively. The amiloride sensitive Na ÷ conductance was, however, inhibited when the wt-CFTR CI-conductance was activated by phosphodiesterase inhibition (IBMX). In contrast, IBMX had no such effect in AF508 and Na ÷ channels coexpressing oocytes. These results suggest that wt-CFTR, but not AF508-CFTR, is a cAMP dependent downregulator of epithelial Na + channels. This may explain the higher Na ÷ conductance observed in airway epithelial cells of CF patients.

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After decades of unsuccessful efforts in inhibiting KRAS, promising clinical data targeting the mutation subtype G12C emerge. Since little is known about outcome with standard treatment of patients with G12C mutated non-small cell lung cancer (NSCLC), we analyzed a large, representative, real-world cohort from Germany. Patients and methods: A total of 1039 patients with advanced KRAS-mutant or-wildtype NSCLC without druggable alterations have been recruited in the prospective, observational registry CRISP from 12/2015 to 06/2019

Oocytes from Xenopus laevis activate a Ca2+ dependent Cl- conductance when exposed to the Ca2+ ionophore ionomycin. This Ca2+ activated Cl- conductance (CaCC) is strongly outwardly rectifying and has a halide conductivity ratio (GI- / GCl-) of about 4.4. This is in contrast to the cystic fibrosis transmembrane conductance regulator (CFTR)-Cl- conductance, which produces more linear I/V curves with a GI- / GCl- ratio of about 0.52. Ionomycin enhanced CaCC (DeltaG) in water injected and CFTR expressing ooyctes in the absence of 3-isobutyl-1-methylxanthine (IBMX, 1 mmol/l) by (microS) 23 +/- 1.9 (n=9) and 23.6 +/- 2.3 (n=11). Stimulation by IBMX did not change CaCC in water injected oocytes. CaCC was inhibited in CFTR-expressing ooyctes after stimulation with IBMX or a membrane permeable form of cAMP and was only 5.1 +/- 0.48 microS (n=18) and 6. 9 +/- 0.6 (n=3), respectively. Inhibition of CaCC was correlated to the amount of CFTR-current activated by IBMX. DeltaF508-CFTR which demonstrates only a small residual function in activating a cAMP dependent Cl- channel in oocytes inhibited CaCC to a lesser degree (DeltaG=12.1 +/- 1.1 microS; n=7). Changes of CFTR and CaCC-Cl- whole cell conductances were also measured when extracellular Cl- was replaced by I-. The results confirmed the reduced activation of CaCC in the presence of activated CFTR. No evidence was found for inhibition of CFTR-currents by increase of intracellular Ca2+. Moreover, intracellular cAMP was not changed by ionomycin and stimulation by IBMX did not change the ionomycin induced Ca2+ increase in Xenopus oocytes. Taken together, these results suggest that activation of CFTR-Cl- currents is paralleled by an inhibition of Ca2+ activated Cl- currents in ooyctes of Xenopus laevis. These results provide another example for CFTR-dependent regulation of membrane conductances other than cAMP-dependent Cl- conductance. They might explain previous findings in epithelial tissues of CF-knockout mice.

Cystic fibrosis transmembrane conductance regulator (CFTR) functions as a Cl- channel in a large variety of cells expressing this protein. Recently evidence has accumulated that it also regulates other ion channels. A coordinated increase in Cl- and K+ conductances is necessary in many Cl--secreting epithelia. This has, for example, recently been demonstrated for the colonic crypt, for which a new type of K+ channel and a specific inhibitor of this channel, the chromanol 293B, have been described. In the present study we have examined whether the cAMP-evoked activation of CFTR, overexpressed in Xenopus oocytes, in addition to its known activation of a Cl- conductance, also upregulates endogenous K+ channels. It is shown that CFTR-cRNA-injected but not water-injected oocytes possess a cAMP-activated Cl- conductance. Of the cAMP-induced whole-cell current increase, 15-25% was due to a 293B-, Ba2+and TEA+-inhibitable K+ conductance. The cRNA of the mutated CFTR (DeltaF508 CFTR) had no such effect. We conclude that cAMP activated CFTR and an endogenous IsK-type and 293B-sensitive K+ conductance. Similar events, occurring, for example, in the colonic crypt possessing CFTR and 293B-sensitive K+ channels, might explain the coordinated cAMP-mediated increase in Cl- and K+ conductances.