NITRIC-OXIDE RESPONSE TO SHEAR-STRESS BY HUMAN BONE CELL-CULTURES IS ENDOTHELIAL NITRIC-OXIDE SYNTHASE DEPENDENT

Bone cells, in particular osteocytes, are extremely sensitive to shear stress, a phenomenon that may be related to mechanical adaptation of bone. In this study we examined whether human primary bone cells produ ce NO in response to fluid shear stress and established by RT/PCR whic h NOS isoforms were expressed before and after application of shear st ress. One hour pulsating fluid flow (PFF; 0.7 +/- 0.02 Pa, 5 Hz) cause d a rapid (within 5 min) 2 to 4-fold increase in NO production. NO rel ease was only transiently increased during the first 15 min of exposur e to PFF, and remained at control levels during a 1-24 hr postincubati on period, In both control and PFF-treated cells, mRNA was easily dete cted for ecNOS, but not nNOS, and only minimal amounts iNOS were found , mRNA levels for ecNOS increased 2-fold at 1 hr after 1 hr PFF treatm ent. These results suggest that the rapid production of NO by human bo ne cells in response to fluid flow results from activation of ecNOS. P FF also leads to an increase in ecNOS mRNA which is likely related to the shear stress responsive element in the promoter of ecNOS. (C) 1998 Academic Press.