In the case of epithelia from CF patients with CFTR channel gating mutations, add 20 μM forskolin or 100 μM CPT-cAMP in order to maximize CFTR activation, and subsequently add a potentiator compound on apical side (e.g., 50 μM genistein or 1 μM ivacaftor) to further stimulate channel opening. The gene discussed is CFTR; the disease is cystic fibrosis.