Mechanical stretching of alveolar epithelial cells increases Na⁺-K⁺- ATPase activity

Alveolar epithelial cells effect edema clearance by transporting Na⁺ and liquid out of the air spaces. Active Na⁺ transport by the basolaterally located Na⁺-K⁺-ATPase is an important contributor to lung edema clearance. Because alveoli undergo cyclic stretch in vivo, we investigated the role of cyclic stretch in the regulation of Na⁺-K⁺-ATPase activity in alveolar epithelial cells. Using the Flexercell Strain Unit, we exposed a cell line of murine lung epithelial cells (MLE-12) to cyclic stretch (30 cycles/min). After 15 min of stretch (10% mean strain), there was no change in Na⁺-K⁺- ATPase activity, as assessed by ⁸⁶Rb⁺ uptake. By 30 min and after 60 min, Na⁺-K⁺-ATPase activity was significantly increased. When cells were treated with amiloride to block amiloride-sensitive Na⁺ entry into cells or when cells were treated with gadolinium to block stretch-activated, nonselective cation channels, there was no stimulation of Na⁺-K⁺-ATPase activity by cyclic stretch. Conversely, cells exposed to Nystatin, which increases Na⁺ entry into cells, demonstrated increased Na⁺K⁺ATPase activity. The changes in Na⁺-K⁺-ATPase activity were paralleled by increased Na⁺-K⁺-ATPase protein in the basolateral membrane of MLE-12 cells. Thus, in MLE-12 cells, short-term cyclic stretch stimulates Na⁺-K⁺-ATPase activity, most likely by increasing intracellular Na⁺ and by recruitment of Na⁺-K⁺-ATPase subunits from intracellular pools to the basolateral membrane.