Minimally modified LDL upregulates endothelin type A receptors in rat coronary arterial smooth muscle cells.

Minimally modified low-density lipoprotein (mmLDL) is a risk factor for cardiovascular disease. The present study investigated the effects of mmLDL on the expression of endothelin type A (ET(A)) receptors in coronary arteries. Rat coronary arteries were organ-cultured for 24 h. The contractile responses were recorded using a myographic system. ET(A) receptor mRNA and protein expressions were determined using real-time PCR and western blotting, respectively. The results showed that organ-culturing in the presence of mmLDL enhanced the arterial contractility mediated by the ET(A) receptor in a concentration-dependent and time-dependent manner. Culturing with mmLDL (10  μ g/mL) for 24 h shifted the concentration-contractile curves toward the left significantly with increased E(max) of 228% ± 20% from control of 100% ± 10% and significantly increased ET(A) receptor mRNA and protein levels. Inhibition of the protein kinase C, extracellular signal-related kinases 1 and 2 (ERK1/2), or NF- κ B activities significantly attenuated the effects of mmLDL. The c-Jun N-terminal kinase inhibitor or the p38 pathway inhibitor, however, had no such effects. The results indicate that mmLDL upregulates the ETA receptors in rat coronary arterial smooth muscle cells mainly via activating protein kinase C, ERK1/2, and the downstream transcriptional factor, NF- κ B.