Effect of cyclic stretch on alpha-subunit mRNA expression of Na+-K+-ATPase in aortic smooth muscle cells

We previously demonstrated that protein expression of both alpha(1)- and alpha(2)-catalytic subunits of the Na+-K+-ATPase is elevated after a 2- to 4-day chronic cyclic stretch regimen in cultured aortic smooth muscle cells (ASMC). In the present study, we investigated whether cyclic stretch affects mRNA expression of the alpha-isoforms of the Na+-K+-ATPase. Using a stretch apparatus, rat ASMC were cyclically stretched 10 or 20% of their length for 1, 3, or 6 h. alpha-Isoform mRNA levels were measured using Northern analysis. A 3-h 10% stretch had no significant affect on mRNA expression for either isoform, but a 20% stretch increased mRNA of both isoforms approximately twofold. Whereas a 6-h 20% stretch increased alpha(1) mRNA by 3.3-fold, alpha(2) was not affected any further. Actinomycin D blocked the stretch-induced stimulation of mRNA expression of both alpha-subunits. In conclusion, cyclic stretch stimulates the mRNA expression of both alpha(1)- and alpha(2)-subunits of Na+-K+-ATPase. The sensitivity of the two genes to the degree and duration of stretch is different. The stretch-induced increase of mRNA may be a result of increased transcription.