CELL-GROWTH AND NA-K-CL COTRANSPORT RESPONSES OF VASCULAR SMOOTH-MUSCLE CELLS OF MILAN RATS

The present study examines the role of serum growth factors in the proliferative response and Na-K-Cl cotransport activity of vascular smooth muscle cells from Milan normotensive (MNS) and hypertensive (MHS) rats. Cells from thoracic aorta of both strains were cultured in 10% serum medium and made quiescent by 72 hours in 0.3% serum medium. MHS cells grown with 10% serum had a shorter population doubling time than MNS cells between passages 8 and 12 (13.8+/-1.7 versus 20.1+/-1.6 hours, P<.0l, n=4). MHS cells also exhibited a higher response of thymidine incorporation into nucleic acid to serum, epidermal, and platelet-derived growth factor BB. In MHS cells epidermal (100 ng/mL) and platelet (50 ng/mL) growth factors increased thymidine incorporation 2- and 10-fold, respectively. In MNS cells epidermal factor did not induce a significant response, and that of platelet factor was twofold lower than in MHS cells. Binding curves revealed a higher number of receptors for platelet than epidermal growth factor in both strains and a similar number of both receptors in MHS and MNS cells. Quantitative immunoblots of these receptor proteins confirmed the observation that the greater proliferation of MHS cells could not be related to a higher number of growth factor receptors. Cotransport activity (bumetanide-sensitive Rb-86 influx in nanomoles per milligram protein per 5 minutes) was found to be significantly higher in MHS cells (16+/-3, n=18) than MNS cells (8+/-3, n=15) at confluence as well as in the log phase of serum-stimulated growth. No differences were found between strains with cells in the quiescent state. However, platelet growth factor (50 ng/mL) markedly stimulated cotransport in quiescent MHS cells, whereas epidermal growth factor was without effect. In conclusion, MHS cells exhibited enhanced serum- and platelet factor-stimulated proliferation rates and cotransport activity compared with MNS cells. These results suggest that platelet factor BB plays an important role in the proliferation of hypertensive vascular cells.