Myosin-Va restrains the trafficking of Na⁺/K⁺-ATPase-containing vesicles in alveolar epithelial cells

Stimulation of Na⁺/K⁺-ATPase activity in alveolar epithelial cells by cAMP involves its recruitment from intracellular compartments to the plasma membrane. Here, we studied the role of the actin molecular motor myosin-V in this process. We provide evidence that, in alveolar epithelial cells, cAMP promotes Na⁺/K⁺-ATPase recruitment to the plasma membrane by increasing the average speed of Na⁺/K⁺-ATPase- containing vesicles moving to the cell periphery. We found that three isoforms of myosin-V are expressed in alveolar epithelial cells; however, only myosin-Va and Vc colocalized with the Na⁺/K⁺-ATPase in intracellular membrane fractions. Overexpression of dominant-negative myosin-Va or knockdown with specific shRNA increased the average speed and distance traveled by the Na⁺/K⁺-ATPase-containing vesicles, as well as the Na⁺/K⁺-ATPase activity and protein abundance at the plasma membrane to similar levels as those observed with cAMP stimulation. These data show that myosin-Va has a role in restraining Na⁺/K⁺-ATPase-containing vesicles within intracellular pools and that this restrain is released after stimulation by cAMP allowing the recruitment of the Na⁺/K⁺-ATPase to the plasma membrane and thus increased activity.