EVIDENCE FOR DIFFERENCES IN CULTURED LEFT-VENTRICULAR FIBROBLAST POPULATIONS ISOLATED FROM SPONTANEOUSLY HYPERTENSIVE AND WISTAR-KYOTO RATS

Objective: To compare fibroblast populations derived from spontaneousl y hypertensive rats (SHR(LJ)) and normotensive Wistar-Kyoto rats (WKYL J) for angiotensin II receptor binding, gene expression of the AT(1) r eceptor and angiotensinogen, hormone responsiveness and phenotypic cha nges. Methods: Fibroblasts were isolated by either collagenase B or co llagenase P and grown to confluency in the presence of 10% fetal bovin e serum. Angiotensin II receptor binding was assessed under both serum and serum-free conditions. Hormonal treatment of cells was conducted in a serum-free background. The concentrations of AT(1) receptor and a ngiotensinogen messenger RNA (mRNA) were determined by liquid hybridiz ation. Phenotypic changes in fibroblast populations were analysed by v isualization of lipid-containing vacuoles (oil red O stain) or of alph a-smooth muscle actin-containing fibres (immunostain). Results: SHR(LJ ) collagenase-B cells grew more slowly and had nearly twofold fewer an giotensin II receptors than WKYLJ cells as measured by both radioligan d binding and AT(1) mRNA content (SHR(LJ) 1.34 +/- 0.05 versus WKYLJ 5 .94 +/- 0.41 pg mRNA per mu g total RNA) but contained significantly m ore angiotensinogen mRNA (SHR(LJ) 147 +/- 12 versus WKYLJ 98 +/- 8 fg mRNA per mu g total RNA). Collagenase-P cells from the two strains exh ibited similar binding and growth properties. Collagenase-B fibroblast s also exhibited greater responses to exogenous steroids, including a greater shift towards an adipocyte phenotype, than collagenase-P cells . Exogenous angiotensin II promoted transformation towards a myofibrob last cell type, especially in collagenase-P SHR(LJ) cells. Conclusion: Our results indicate that subsets of fibroblasts that differ in growt h rate, angiotensin II receptor binding, AT(1) and angiotensinogen mRN A levels, structure and steroid responsiveness may be isolated from th e left ventricle. The potential importance of these altered phenotypes to cardiac remodelling and hypertrophy warrants further examination.