Figure 10.
Modulation of CFTR gating by MgAMP-PNP. (A) A continuous recording shows that MgAMP-PNP locks open CFTR shortly after ATP removal (relaxation time constant, τ = 47.5 ± 7.3 s; n = 5). This effect was nearly completely abolished by mixing 2 mM MgAMP-PNP with 5 mM ADP. After a long nucleotide washout, 2 or 10 mM MgAMP-PNP induced short openings (ensemble current relaxation, τ = 1.61 s; n = 5). (B) WT channels were exposed to 2 mM MgAMP-PNP plus 10 mM (left) or 2 mM ATP (right) after PKA activation. Parameters yielded by double-exponential fit are Fslow = 51 ± 4.3%, τfast = 0.57 ± 0.17, and τslow = 40.2 ± 4.9 s (n = 5; 2 mM MgAMP-PNP plus 10 mM ATP) and Fslow = 73 ± 3%, τfast = 0.45 ± 0.06, and τslow = 45.7 ± 7.1 s (n = 6; 2 mM MgAMP-PNP plus 2 mM ATP). (C) Y1219G channels opened by ATP plus PKA were locked open by 2 mM MgAMP-PNP plus 2 mM ATP. The bi-exponential current decay gives Fslow = 71 ± 4%, τfast = 0.45 ± 0.03, and τslow = 36.7 ± 4.1 s (n = 6). Arrows in B and C indicate the beginning of the slow component.