AICAR activates AMPK and alters PIP 2 association with the epithelial sodium channel ENaC to inhibit Na + transport in H441 lung epithelial cells

Changes in amiloride‐sensitive epithelial Na + channel (ENaC) activity ( NP o ) in the lung lead to pathologies associated with dysregulation of lung fluid balance. UTP activation of purinergic receptors and hydrolysis of PIP 2 via activation of phospholipase C (PLC) or AICAR activation of AMP‐activated protein kinase (AMPK) inhibited amiloride‐sensitive Na + transport across human H441 epithelial cell monolayers. Neither treatment altered α, β or γ ENaC subunit abundance ( N ) in the apical membrane indicating that the mechanism of inhibition was via a change in channel open state probability ( P o ). We found that UTP depleted PIP 2 abundance in the apical membrane whilst activation of AMPK prevented the binding of β and γ ENaC subunits to PIP 2. The association of PIP 2 with the ENaC subunits is required to maintain channel activity via P o . Thus, these data show for the first time that AICAR activation of AMPK inhibits Na + transport via a mechanism that perturbs the PIP 2 –ENaC channel interaction to alter P o . In addition, we show that dissociation of PIP 2 from ENaC together with activation of AMPK further reduced Na + transport by a secondary effect that correlated with ENaC subunit internalization. Thus, when PIP 2 –ENaC subunit interactions were compromised, ENaC protein retrieval was initiated, indicating that AMPK can modulate ENaC P o and N .