RESUMO
AIM: Angiotensin-converting enzyme (ACE) inhibitors like ramiprilat bind to ACE expressed on the cell surface of endothelial cells and induce cell-specific signalling including the activation of activator protein (AP)-1. The present study addressed the question whether ramiprilat exerts a similar effect on adult ventricular cardiomyocytes, i.e. activates the AP-1 or modifies contractile performance. It was further aimed to decide whether such effects depend on bradykinin receptors or whether they are directly mediated via ACE. METHODS: Adult rat ventricular cardiomyocytes were isolated and cultured. mRNA expression of ACE was investigated by RT-PCR, AP-1 activation by gel mobility shift assays, and cardiac contractile performance by electrical pacing of isolated cells and analysis of cell shortening via a line-camera. RESULTS: Cardiomyocytes stably express ACE. Ramiprilat increased maximal contraction velocity and shortened the time-to-peak of contraction. In contrast to effects evoked by bradykinin, such effects caused by ramiprilat were not attenuated by HOE 140, a bradykinin-receptor antagonist. These effects were also not attenuated in the presence of l-nitro-arginine, used to mimic bradykinin-dependent signalling. In cardiomyocytes, bradykinin but not ramiprilat activated AP-1. Ramiprilat activates AP-1 in endothelial cells that are known to respond to ramiprilat in this way. CONCLUSION: Ramiprilat exerts direct, bradykinin-receptor independent effects on cardiomyocytes that improve cellular function without a corresponding effect on AP-1 activation or induction of AP-1 dependent effects. This newly described effect of ramiprilat may contribute to the protective effects seen by application of ACE inhibitors.
