Cardiac hypertrophy is a major adaptational mechanism in stresses such as pressure overload and neurohumoral stimulation.As powerful vasoconstrictor peptides in cardiovascular system,especially the vascular endothelium,smooth muscle cells and cardiocyte,ETs play important physiological roles in the regulation of normal cardiovascular function.Excessive generation of ETs in local cardiac muscle has been linked to myocardial hypertrophy.Endothelin-1(ET-1) in cardiac muscle exerts its actions in the development of myocardial hypertrophy through binding to specific receptors and interacting with other vasoactive substance of local tissues.ET-1 can induce the hypertrophy for cardiocytes and the proliferation for cardiac fibroblasts by ETA.ETB receptors are implicated both in initiating and maintaining myocardial hypertrophy.As a new target of drug,ET receptors have become the research focus,and great progress has been made on the development of the ET antagonists.

In the present study, the specifically knockdown models of P-gp or MRP2 were constructed by using a series of chemically synthesized small interfering RNA (siRNA) in vitro. The expression of P-gp and MRP2 was measured by real-time PCR and Western blot, and the function was evaluated by applying P-gp and MRP2 substrate, rhodamine and methotrexate. The results showed that MRP2 siRNA-3 or P-gp siRNA-2 significantly decreased the mRNA expression of MRP2 or P-gp, the inhibition ratio was 68% or 84%; MRP2 siRNA-3 or P-gp siRNA-2 at a dose of 80 nmol x L(-1) significantly reduced the protein expression of MRP2 or P-gp at 48 h after treatment, the inhibition ratio was 62% or 70%. Meanwhile, other transporters were not influenced by siRNA. When pretreatment with MRP2 siRNA-3 or P-gp siRNA-2, the efflux of methotrexate or rhodamine decreased significantly and the intra-cellular concentration increased. The results suggested that chemically synthesized siRNA could significantly inhibit the expression and function of MRP2 and P-gp, and the model of RNAi in vitro could be used to evaluate the role of efflux transporters in transportation of drugs.