Respiratory dysfunction progresses with age in Kcna1-null mice, a model of sudden unexpected death in epilepsy

Objective: Increased breathing rate, apnea, and respiratory failure are associated with sudden unexpected death in epilepsy (SUDEP). We recently demonstrated the progressive nature of epilepsy and mortality in Kcna1^−/− mice, a model of temporal lobe epilepsy and SUDEP. Here we tested the hypothesis that respiratory dysfunction progresses with age in Kcna1^−/− mice, thereby increasing risk of respiratory failure and sudden death (SD). Methods: Respiratory parameters were determined in conscious mice at baseline and following increasing doses of methacholine (MCh) using noninvasive airway mechanics (NAM) systems. Kcna1^+/+, Kcna1^+/−, and Kcna1^−/− littermates were assessed during 3 age ranges when up to ~30%, ~55%, and ~90% of Kcna1^−/− mice have succumbed to SUDEP: postnatal day (P) 32-36, P40-46, and P48-56, respectively. Saturated arterial O₂ (SaO₂) was determined with pulse oximetry. Lung and brain tissues were isolated and Kcna1 gene and protein expression were evaluated by reverse transcriptase quantitative polymerase chain reaction (RT-qPCR) and Western blot techniques. Airway smooth muscle responsiveness was assessed in isolated trachea exposed to MCh. Results: Kcna1^−/− mice experienced an increase in basal respiratory drive, chronic oxygen desaturation, frequent apnea-hypopnea (A-H), an atypical breathing sequence of A-H-tachypnea-A-H, increased tidal volume, and hyperventilation induced by MCh. The MCh-provoked hyperventilation was dramatically attenuated with age. Of interest, only Kcna1^−/− mice developed seizures following exposure to MCh. Seizures were provoked by lower concentrations of MCh as Kcna1^−/− mice approached SD. MCh-induced seizures experienced by a subset of younger Kcna1^−/− mice triggered death. Respiratory parameters of these younger Kcna1^−/− mice resembled older near-SD Kcna1^−/− mice. Kcna1 gene and protein were not expressed in Kcna1^+/+ and Kcna1^+/− lungs, and MCh-mediated airway smooth muscle contractions exhibited similar half-maximal effective concentration(EC₅₀) in isolated Kcna1^+/+ and Kcna1^−/− trachea. Significance: The Kcna1^−/− model of SUDEP exhibits progressive respiratory dysfunction, which suggests a potential increased susceptibility for respiratory failure during severe seizures that may result in sudden death.