Expression of functional angiotensin-converting enzyme and AT(1) receptorsin cultured human cardiac fibroblasts

Background-Angiotensin II (Ang II) has been implicated in the development o f cardiac fibrosis. The aims of the present study were to examine expressio n and activity of ACE and of angiotensin receptors in human cardiac fibrobl asts cultured from dilated cardiomyopathic and ischemic hearts. The effects of Ang II on fibroblasts were also investigated. Methods and Results-Human cardiac fibroblasts were cultured from ventricula r and atrial myocardium and characterized immunohistochemically. Expression of ACE and the angiotensin AT(1) receptor was demonstrated in cardiac fibr oblasts by reverse transcriptase-polymerase chain reaction and radioligand binding. Functional ACE activity, measured by radiolabeled substrate conver sion assay, was detected in both ventricular (V-max . K-m(-1) . mg(-1), 0.0 31 +/- 0.010; n=13) and atrial (0.034+/-0.012; n=6) fibroblasts. Fibroblast ACE activity was increased after 48 hours of treatment with basic fibrobla st growth factor, dexamethasone, and phorbol ester. Ang II did not affect D NA synthesis but stimulated [H-3]proline incorporation in cardiac fibroblas ts (20.0+/-4.0% increase above control by 10 mu mol/L; P<0.05, n=7), which was abolished by losartan 10 mu mol/L but not PD123319 1 mu mol/L. Ang II a lso stimulated a rise in intracellular calcium (basal, 56+/-1 nmol/L; Ang I I, 355+/-24 nmol/L) via the AT(1) receptor, as shown by complete inhibition with losartan. Conclusions-We have demonstrated expression and activity of ACE and AT(1) r eceptor in cultured human cardiac fibroblasts. In addition, cardiac fibrobl asts respond to Ang II with AT(1) receptor-mediated collagen synthesis. The presence of local ACE and AT(1) receptors in human fibroblasts suggests th eir involvement in the development of cardiac fibrosis.