As seen in adult CF knockout rats (Tuggle et al., 2014), G452X knockin rats exhibit the unique electrophysiological phenotype with constitutively active baseline CFTR current in ex vivo tracheal sections, prior to cAMP stimulation (Figure 3 and Supplementary Figure 1), as opposed to the neonatal rats where pre-activation is not apparent (McCormick et al., 2018). The gene discussed is CFTR; the disease is cystic fibrosis.