ANGIOTENSIN-CONVERTING ENZYME AND KININASE-II-LIKE ACTIVITIES IN CULTURED VALVULAR INTERSTITIAL-CELLS OF THE RAT-HEART

Objective: The function of angiotensin converting enzyme (ACE) at cell sites of high collagen turnover, such as heart valves, is uncertain. The aim of this study was to assess ACE and kininase-II-like activitie s and collagen turnover in cultured valvular interstitial cells of the adult rat heart. Methods: The valvular interstitial cell phenotype wa s determined by immunolabelling (rhodamine phalloidin, desmin, and Gri ffonia simplicifolia lectin), and the presence of ACE mRNA and protein was confirmed by reverse transcriptase-polymerase chain reaction anal ysis, ACE monoclonal antibody and in vitro autoradiography, respective ly. ACE and kininase-II-like activities in valvular interstitial cells were analysed by high performance liquid chromatography. Angiotensin II (AT,) and bradykinin receptors in valvular interstitial cell membra nes were examined by western immunoblotting and binding assay. Type I collagen and collagenase in valvular interstitial cell culture media w ere determined by ELISA and zymography, respectively. Type I collagen mRNA expression in cultured valvular interstitial cells was determined by northern blot analysis and in situ hybridisation. Results: In inta ct valvular interstitial cells or their cell membrane we found: (1) ac tin microfilaments, but not desmin or lectin labelling; (2) ACE mRNA e xpression and binding activity; (3) conversion of angiotensin I to ang iotensin II, which was completely inhibited by 50 mu M lisinopril, whi le kininase-II-like activity exceeded ACE activity and was not inhibit ed by lisinopril; (4) AT, and bradykinin receptors in valvular interst itial cell membrane preparations; (5) type I collagen mRNA expression and collagenase activity; and (6) angiotensin II. induced increase in type I collagen synthesis and mRNA expression. Conclusions: Cultured v alvular interstitial cells represent a nonendothelial, non-smooth-musc le cell type that expresses mRNA for ACE and type I collagen. ACE and kininase-II-like activities in valvular interstitial cells may be invo lved in the regulation of peptides that influence collagen turnover. A ngiotensin II stimulates type I collagen synthesis and mRNA expression in these cells.