Long-term terbutaline exposure stimulates α₁-Na⁺-K⁺-ATPase expression at posttranscriptional level in rat fetal distal lung epithelial cells

Abstract

Transepithelial Na(+) transport through epithelial Na(+) channels (ENaC) on the apical membrane and Na(+)-K(+)-ATPase activity on the basolateral membrane of distal lung epithelial cells are critical for alveolar fluid clearance. Acute exposure to beta-adrenergic agonists stimulates lung fluid clearance by increasing Na(+) transport. We investigated the effects of chronic exposure to the beta(2)-adrenergic agonist terbutaline on the transepithelial Na(+) transport in rat fetal distal lung epithelia (FDLE). FDLE monolayers exposed to 10(-4) M terbutaline for 48 h had significantly increased propanolol-blockable transepithelial total and amiloride-sensitive short-circuit current (I(sc)); however, when these chronically exposed monolayers were acutely exposed to additional beta-agonists and intracellular cAMP upregulators, there was no further increase in I(sc). Monolayers exposed to terbutaline for >48 h had I(sc) similar to control cells. Ouabain-sensitive Na(+)-K(+)-ATPase activity was increased in 48-h terbutaline-exposed FDLE whose apical membranes were permeabilized with nystatin. In contrast, terbutaline did not increase amiloride-sensitive apical membrane I(sc) in FDLE whose basolateral membranes were permeabilized with nystatin. Terbutaline treatment did not affect alpha-, beta-, or gamma-ENaC mRNA or alpha-ENaC protein steady-state levels, but increased total cellular levels and rate of synthesis of alpha(1)-Na(+)-K(+)-ATPase protein in FDLE in the absence of any change in alpha(1)-Na(+)-K(+)-ATPase mRNA. Total cellular beta(1)-Na(+)-K(+)-ATPase mRNA and protein levels were not affected by terbutaline. These data suggest that FDLE have different responses from adult type II epithelial cells when chronically exposed to terbutaline, and their increased transepithelial Na(+) transport occurs via a posttranscriptional increase in alpha(1)-Na(+)-K(+)-ATPase expression.

Lipopolysaccharide Inhibits Alpha Epithelial Sodium Channel Expression via MiR-124-5p in Alveolar Type 2 Epithelial Cells

“…en, the membranes were incubated with primary antibody: α-ENaC antibody (PA1-920A, ermo Fisher) and β-actin (sc-47778, Santa Cruz Biotechnology) at 1 : 2000 in TBSTcontaining 5% BSA at 4°C overnight. e specific band between 70 and 100 kDa for α-ENaC protein could be seen, according to the manufacturer's manual and previous studies [18]. Following washing three times with TBST, membranes were incubated with HRP conjugated goat-anti-rabbit or goat-anti-mouse secondary antibody at 1 : 2000 at room temperature for 1 h and then washed for 10 min with TBST three times.…”

Lipoxin A4Activates Alveolar Epithelial Sodium Channel, Na,K-ATPase, and Increases Alveolar Fluid Clearance

“…This solute transport drives osmotic water transport, and accordingly alveolar fluid clearance (AFC) (2). Na 1 ions enter alveolar type II (ATII) epithelial cells at the apical surface, primarily through amiloride-sensitive sodium channels, such as the epithelial sodium channel (ENaC), and are pumped out on the basolateral surface by Na,K-ATPase (3,4).…”

Sodium Transport and Alveolar Fluid Clearance in Acute Lung Injury

“…PKA augments the number of HSCs, increases NSC activity, and upregulates Na + , K + -ATPase and CFTR [73,79]. However, FDLEs exposed to the β2-adrenergic agonist terbutaline have increased Na + transport via a post-transcriptional increase in α1-Na + , K + -ATPase protein expression, without significant effects on β1-Na + , K + -ATPase and ENaC [25], suggesting that β2-adrenergic agonists play different roles in ion transport in adult and foetal distal lung epithelium. Furthermore, prolonged treatment with terbutaline impairs β 2AR signalling in the alveolar epithelia and whole lungs [32].…”

“…The β-subunit is necessary for the stability and trafficking of this combination [23]. The α 1-, α2-, β1-isoform of Na + , K + -ATPase (α1-, α2-, β1-Na + , K + -ATPase) has been discovered in lung epithelial cells [25]. Additionally, α1-Na + , K + -ATPase has been reported to be expressed by AT II cells, α1and α2-Na + , K + -ATPase can be found on AT I cells [26].…”