Key words Cl
Springer Online Journal Archives 1860-2000
Abstract 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 (ΔF508 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.
Type of Medium: