A revised CFTR gating scheme showing hypothetical conformational transitions that take place during an opening burst. C1, closed state with two separated NBDs; C2, partial NBD dimeric closed state; O1, prehydrolytic open state; O1′, post-hydrolytic open state with a full NBD dimer; X, the newly identified state with a partially separated NBD dimer; X′, one ATP bound to the vacant ABP2 in state X. *, the ATP-independent, short-lived flickery closed events that are discounted in data analysis and interpretation (see Discussion for details). The red box encompasses the reentry pathway that may occur within each opening burst.