ANGIOTENSIN II-STIMULATED PHOSPHOLIPASE-C RESPONSES OF 2 VASCULAR SMOOTH MUSCLE-DERIVED CELL-LINES ROLE OF CYCLIC-GMP

Vascular smooth muscle cells of the spontaneously hypertensive rat (SH R) are known to show increased responsiveness to angiotensin II (Ang I I) compared with cells of normotensive control Wistar-Kyoto rats (WKY) . We investigated the hy hypothesis that differential levels of cGMP l ead to the different responsiveness of the cells, using vascular smoot h muscle cells in culture. cGMP levels in extracts of SHR-derived cell s were lower than those of WKY-derived cells. This was true for both u nstimulated cells and cells treated with equal concentrations of eithe r sodium nitroprusside or S-nitroso-N-acetylpenicillamine. Stimulation of cells with Ang II did not affect levels of cGMP but increased leve ls of inositol 1,4,5-trisphosphate (IP3) and Ca2+ which were greater i n SHR- than in WKY-derived cells. When SHR and WKY cells were preincub ated with different concentrations of S-nitroso-N-acetylpenicillamine to generate similar cGMP levels in each cell type, the subsequent IP3 response to Ang II was the same in the two cell types. To reduce any i nfluence of cGMP on responses, we permeabilized the cells with alpha-t oxin. Stimulation of alpha-toxin-permeabilized cells with high Ca2+ re vealed an IP3 response in SHR- but not WKY-derived cells. Similarly, p ermeabilized SHR cells responded to Ang II but WKY cells did not. Howe ver, GTP and GTP gamma S elevated IP3 in both cell types. Taken togeth er, these results indicate that the low response of WKY cells can be a ccounted for by the inhibitory influence of cGMP. However, when this i nhibition is removed by permeabilization, further differences between the cells are revealed that will contribute to the elevated SHR respon se.