Growth response of human coronary smooth muscle cells to angiotensin II and influence of angiotensin AT₁ receptor blockade

Background: The renin-angiotensin system has been implicated in the development of vascular wall thickening in cardiovascular disease, through the growth-promoting actions of the vasoconstrictive agent, angiotensin II, on vascular smooth muscle cells.

Objective: To investigate the effect of angiotensin II on growth of human coronary artery smooth muscle cells (cSMCs) in culture, and to identify the angiotensin receptor(s) mediating such a response.  Human cSMCs were isolated from coronary arteries of recipient hearts obtained during transplantation, and characterized by immunohistochemistry. The effect of angiotensin II on protein synthesis by cSMCs was measured by [³H]leucine incorporation and protein concentration assays. Human cSMC proliferation was assessed by [³H]thymidine incorporation assay and cell count. Reverse transcriptase polymerase chain reaction (RT-PCR) was used to detect angiotensin receptor expression. Transient increases in intracellular calcium concentration in cSMCs in response to angiotensin II stimulation were visualized under fura-2 fluorescence microscopy. 

Results:  Angiotensin II (1 nmol/l-10 μmol/l) stimulated protein synthesis in cSMCs (maximum 24 ± 2% increase in incorporation of [³H]leucine over 48 h; n = 4, P < 0.01). An increase in cellular protein content was also measured. However, angiotensin II had no effect on proliferation of quiescent cSMCs. The increased protein synthesis was completely inhibited by pretreatment with the angiotensin AT₁ receptor antagonist, losartan, but not the AT₂ receptor antagonist, PD123319. Expression of the angiotensin AT₁ receptor subtype was detected in cSMCs by RT-PCR, Angiotensin II stimulation of cells triggered transient increases in intracellular calcium concentration, which were abolished by losartan, but were insensitive to PD123319 and pertussis toxin.

Conclusions: The results of this study in human coronary VSMCs indicate that angiotensin II and the AT₁ receptor may be involved in the development of coronary artery disease in man.