Aim: To investigate the effects of the osmolarity on the NO synthase (NOS) activity in endothelial cells and explore their mechanism.
Methods: The endothelial cells were exposed to hypotonic (205 mOsm) or hypertonic (410 mOsm) in culture medium. Griess assay was used to measure NOS activity in cells. The inducible NOS (iNOS) and endothelial NOS (eNOS) gene expression were detected by Northern blot method.
Results: After exposed to hypotonic or hypertonic medium NOS activity of eEND cells increased significantly compared with that of endothelial cells cultured in isotonic medium (305 mOsm). The increases induced by non isotonic changed in time-dependent model. The effect of hypotonic on NOS activity was more significant than that of hypertonic. Dexamethasone had no effect on the increases of NOS activity induced by non-isotonic osmolarity. Cycloheximide suppressed NOS activity via inhibiting protein synthesis but in cycloheximide treated cells, but hypotonic or hypertonic still caused significant increase in NOS activity over the control. The results of Northern blot analysis showed that hypotonic and hypertonic induced the increase of eNOS gene expression, but had no effect on iNOS gene.
Conclusion: Hypotonic and hypertonic specifically increased eNOS activity in endothelial cells, in which the increase of eNOS gene expression may play an important role.