title: Regulation of Na+,K+-ATPase alpha-subunit expression by mechanical strain in aortic smooth muscle cells.
abstract: We have previously demonstrated that vascular sodium pump activity is stimulated in several rat models of hypertension. In addition, others have reported an upregulation of mRNA for the Na+,K+-ATPase alpha1-subunit in hypertension. To test the effect of sustained, cyclic, stretch-relaxation stimuli on the expression of alpha1- and alpha2-subunits of Na+,K+-ATPase in vascular smooth muscle cells, we used the Flexercell strain unit to stretch rat aortic smooth muscle cells for several days on a collagen-coated silicone elastomer substratum. Six-second cycles of stretch-relaxation were applied to obtain 10% average surface elongation (22% maximum) for 4 days. Control cells were not stretched but were grown on a similar surface. The effect of Gd3+, a blocker of stretch-activated channels, was also investigated. At the end of 4 days, protein expression of alpha1- and alpha2-subunits was determined by Western blot analysis. Intensity of the bands for alpha1- and alpha2-subunits was quantified with the use of a computerized image analyzer. In the stretched cells, both the alpha1- and the alpha2-subunit protein-band intensities were significantly increased compared with those of the non-stretched cells. Treatment with 50 micromol/L Gd3+ during the application of stretch prevented the upregulation of alpha2-expression but not that of alpha1-expression. Sodium pump activity, the functional counterpart of Na+,K+-ATPase, was inhibited as a result of stretch; Gd3+ had no effect on this variable. Our results suggest that in vascular smooth muscle, stretch may be a signal for the upregulation of both the alpha1- and alpha2-isoforms. However, a differential response of the two isoforms to the blocker of stretch-activated channels implies involvement of different mechanisms. This alteration in protein expression is not reflected in the function of the enzyme.
authors.affiliation: Department of Pharmacology, Louisiana State University Medical Center, New Orleans 70112, USA.
authors.forename: E
authors.initials: E
authors.lastname: Songu-Mize
authors.forename: X
authors.initials: X
authors.lastname: Liu
authors.forename: J E
authors.initials: JE
authors.lastname: Stones
authors.forename: L J
authors.initials: LJ
authors.lastname: Hymel
mesh_terms: D000818:Animals; D001011:Aorta / Q000201:enzymology* / Q000473:pathology; D008297:Male; D009131:Muscle, Smooth, Vascular / Q000201:enzymology* / Q000473:pathology; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D017207:Rats, Sprague-Dawley; D000254:Sodium-Potassium-Exchanging ATPase / Q000096:biosynthesis*; D013314:Stress, Mechanical; D015854:Up-Regulation
chemical_list: D012333:RNA, Messenger; D000254:Sodium-Potassium-Exchanging ATPase