Evidence for differences in cultured left ventricular fibroblast populations isolated from spontaneously hypertensive and Wistar-Kyoto rats

To compare fibroblast populations derived from spontaneously hypertensive rats (SHRLJ) and normotensive Wistar-Kyoto rats (WKYLJ) for angiotensin II receptor binding, gene expression of the AT1 receptor and angiotensinogen, hormone responsiveness and phenotypic changes.

Fibroblasts were isolated by either collagenase B or collagenase P and grown to confluency in the presence of 10% fetal bovine 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 AT1 receptor and angiotensinogen messenger RNA (mRNA) were determined by liquid hybridization. Phenotypic changes in fibroblast populations were analysed by visualization of lipid-containing vacuoles (oil red O stain) or of alpha-smooth muscle actin-containing fibres (immunostain).

SHRLJ collagenase-B cells grew more slowly and had nearly twofold fewer angiotensin II receptors than WKYLJ cells as measured by both radioligand binding and AT1 mRNA content (SHRLJ 1.34 +/- 0.05 versus WKYLJ 5.94 +/- 0.41 pg mRNA per microgram total RNA) but contained significantly more angiotensinogen mRNA (SHRLJ 147 +/- 12 versus WKYLJ 98 +/- 8 fg mRNA per microgram total RNA). Collagenase-P cells from the two strains exhibited similar binding and growth properties. Collagenase-B fibroblasts 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 myofibroblast cell type, especially in collagenase-P SHRLJ cells.

Our results indicate that subsets of fibroblasts that differ in growth rate, angiotensin II receptor binding, AT1 and angiotensinogen mRNA levels, structure and steroid responsiveness may be isolated from the left ventricle. The potential importance of these altered phenotypes to cardiac remodelling and hypertrophy warrants further examination.