RESUMO
Proliferation of vascular smooth muscle cells is known to be regulated by autocrine and paracrine stimuli, including extracellular matrix, reactive oxygen species, lipids, and biomechanical forces. The effect of many pharmacological agents to which smooth muscle cells may be exposed, however, is widely unexplored. Ketamine, an intravenous anaesthetic and a phencyclidine derivative, regulates diverse intracellular signalling pathways in smooth muscle cells, several of which are known to affect cell proliferation. The effect of ketamine on proliferative response of smooth muscle cells, however, is not determined. We tested the hypothesis that ketamine may regulate proliferation of smooth muscle cells, and investigated the effects of pharmacological doses of ketamine on their proliferative capacity by measuring DNA synthesis and activation of mitogen-activated protein (MAP) kinase signalling pathway in human aortic smooth muscle cells. DNA synthesis, as determined by incorporation of 3H-thymidine into DNA, was enhanced by 73% (P < 0.0001) and 130% (P < 0.0001) with 10 and 100 microm ketamine, respectively. Ketamine-induced DNA synthesis was dependent on de novo protein synthesis, as it was abolished by an inhibitor of protein synthesis, cycloheximide. A synthetic inhibitor of MAP kinase pathway, PD98059, decreased 50% (P < 0.0001) of ketamine-induced DNA synthesis, suggesting that the activation of MAP kinase pathway was partially responsible for ketamine-induced effects. Consistently, in-gel kinase assay and in vitro kinase assay of cell lysates showed ketamine-induced MAP kinase activation and expression of ERK2 (extracellular signal-regulated kinase) in smooth muscle cells. This effect of ketamine was not dependent on de novo protein synthesis. Immunofluorescent light microscopy showed ketamine-induced nuclear accumulation of c-fos, a downstream effect of MAP kinase activation, in smooth muscle cells. In conclusion, these data support the hypothesis of the study and demonstrate that ketamine, by stimulating DNA synthesis in human aortic smooth muscle cells, may have an impact on proliferative capacity of these cells. The present results also demonstrate that ketamine induces the activation of MAP kinase pathway and nuclear accumulation of transcription factor c-fos in smooth muscle cells. They further demonstrate that the activation of MAP kinases is partially responsible for ketamine-induced DNA synthesis in human aortic smooth muscle cells. Together, these findings suggest that ketamine may play a role as a pharmacological regulator of mechanisms involved in proliferation of smooth muscle cells.
