Pharmacological inhibition of acetylcholine-regulated potassium current (I(K,ACh)) prevents atrial arrhythmogenic changes in a rat model of repetitive obstructive respiratory events

BACKGROUND: In obstructive sleep apnea (OSA), intermittent hypoxemia and intrathoracic pressure fluctuations may increase atrial fibrillation (AF) susceptibility by cholinergic activation. OBJECTIVE: To investigate short-term atrial electrophysiological consequences of obstructive respiratory events, simulated by intermittent negative upper airway pressure (INAP), and the role of atrial acetylcholine-regulated potassium current (I(K,ACh)) activated by the M(2) receptor. METHODS: In sedated (2% isoflurane), spontaneously breathing rats, INAP was applied noninvasively by a negative pressure device for 1 minute, followed by a resting period of 4 minutes. INAP was applied repeatedly throughout 70 minutes, followed by a 2-hour recovery period. Atrial effective refractory period (AERP) and AF inducibility were determined throughout the protocol. To study INAP-induced I(K,ACh) activation, protein levels of protein kinase C (PKC(Ɛ)) were determined in membrane and cytosolic fractions of left atrial (LA) tissue by Western blotting. Moreover, an I(K,ACh) inhibitor (XAF-1407: 1 mg/kg) and a muscarinic receptor inhibitor (atropine: 1 μg/kg) were investigated. RESULTS: In vehicle-treated rats, repetitive INAP shortened AERP (37 ± 3 ms vs baseline 44 ± 3 ms; P = .001) and increased LA membrane PKC(Ɛ) content relative to cytosolic levels. Upon INAP recovery, ratio of PKC(Ɛ) membrane to cytosol content normalized and INAP-induced AERP shortening reversed. Both XAF-1407 and atropine increased baseline AERP (control vs XAF-1407: 61 ± 4 ms; P > .001 and control vs atropine: 58 ± 3 ms; P = .011) and abolished INAP-associated AERP shortening. CONCLUSION: Short-term simulated OSA is associated with a progressive, but transient, AERP shortening and a PKC(Ɛ) translocation to LA membrane. Pharmacological I(K,ACh) and muscarinic receptor inhibition prevented transient INAP-induced AERP shortening, suggesting an involvement of I(K,ACh) in the transient arrhythmogenic AF substrate in OSA.