CYCLIC STRAIN UP-REGULATES NITRIC-OXIDE SYNTHASE IN CULTURED BOVINE AORTIC ENDOTHELIAL-CELLS

In vivo, endothelial cells (EC) are subjected to hemodynamic forces wh ich may influence the production of nitric oxide. This study was desig ned to examine the effect of cyclic strain on the expression of endoth elial nitric oxide synthase (eNOS) in cultured bovine aortic EC. EC we re grown on flexible membranes which were subjected to deformation at 60 cycles/min with -5 or -20 kPa of vacuum. This results in an average strain of 6 and 10%, respectively, which is transmitted to the attach ed cells, Northern blot analysis of total cytosolic RNA demonstrated a n increase in eNOS gene expression with both strain regimens but the i ncrease with 10% average strain was greater than that at 6%. Nuclear r unoff transcription assays confirmed the induction of eNOS transcripts . Western blot analysis showed an increase in eNOS level after 24 h of cyclic 10% average strain compared with controls or 6% average strain . Immunohistochemical staining of EC for eNOS was increased in the hig h strain periphery (7-24% strain) of membranes deformed with -20 kPa v acuum. These results demonstrate that cyclic strain upregulates the ex pression of eNOS transcripts and protein levels in bovine aortic EC th us emphasizing the importance of hemodynamic forces in the regulation of eNOS in vivo.