Short-term stretch translocates the alpha-1-subunit of the Na pump to plasma membrane

Short-term (2 30 min) cyclic stretch activates the Na pump in cultured aortic smooth muscle cells (ASMCs). This effect of stretch involves the phosphotidylinositol 3-kinase (PI 3-kinase) participation. Presently, we investigated whether this stimulation is the result of translocation of Na(+),K(+)-ATPase from endosomes to the plasma membrane. ASMCs were stretched 20% for 5 min using the Flexercell Strain Unit. The plasma membrane and endosome fractions were isolated and Western blotted to localize the Na(+),K(+)-ATPase alpha-1-subunit protein. Membrane marker enzyme, 5' nucleotidase activity, and the early and recycling endosome markers Rab4 and Rab11 were used to verify the enrichment of these fractions. Stretch increased Na(+),K(+)-ATPase alpha-1 expression in plasma membrane fractions and decreased it in endosomes. PI 3-kinase inhibitors LY294002 and wortmannin blocked the stretch-induced translocation of the Na(+),K(+)-ATPase alpha-1-subunit. Rab4 and Rab11 were enriched in the endosomal fraction, whereas 5' nucleotidase activity was enriched in the plasma membrane fraction. We conclude that stimulation of the Na pump activity by shortterm cyclic stretch is the result, at least in part, of transport of the alpha-subunit of the enzyme from endosomes to the plasma membrane.