Mesenteric and hepatic vascular reactivity in Donryu rats with and without a cholesterol-supplemented diet

P2Y1 receptor activation elicits its partition out of membrane rafts and its rapid internalization from human blood vessels: implications for receptor signaling

The nucleotide P2Y(1) receptor (P2Y(1)R) is expressed in both the endothelial and vascular smooth muscle cells; however, its plasma membrane microregionalization and internalization in human tissues remain unknown. We report on the role of membrane rafts in P2Y(1)R signaling by using sodium carbonate or OptiPrep sucrose density gradients, Western blot analysis, reduction of tissue cholesterol content, and vasomotor assays of endothelium-denuded human chorionic arteries. In tissue extracts prepared either in sodium carbonate or OptiPrep, approximately 20 to 30% of the total P2Y(1)R mass consistently partitioned into raft fractions and correlated with vasomotor activity. Vessel treatment with methyl beta-cyclodextrin reduced the raft partitioning of the P2Y(1)R and obliterated the P2Y(1)R-mediated contractions but not the vasomotor responses elicited by either serotonin or KCl. Perfusion of chorionic artery segments with 100 nM 2-methylthio ADP or 10 nM [[(1R,2R,3S,4R,5S)-4-[6-amino-2-(methylthio)-9H-purin-9-yl] 2,3dihydroxybicyclo[3.1.0]hex-1-yl]methyl] diphosphoric acid mono ester trisodium salt (MRS 2365), a selective P2Y(1)R agonist, not only displaced within 4 min the P2Y(1)R localization out of membrane rafts but also induced its subsequent internalization. 2'-Deoxy-N(6)-methyladenosine 3',5'-bisphosphate tetrasodium salt (MRS 2179), a specific P2Y(1)R antagonist, did not cause a similar displacement but blocked the agonist-induced exit from rafts. Neither adenosine nor uridine triphosphate displaced the P2Y(1)R from the membrane raft, further evidencing the pharmacodynamics of the receptor-ligand interaction. Vascular reactivity assays showed fading of the ligand-induced vasoconstrictions, a finding that correlated with the P2Y(1)R exit from raft domains and internalization. These results demonstrate in intact human vascular smooth muscle the association of the P2Y(1)R to membrane rafts, highlighting the role of this microdomain in P2Y(1)R signaling.

Decreased constitutive nitric oxide synthase, but increased inducible nitric oxide synthase and endothelin-1 immunoreactivity in aortic endothelial cells of donryu rats on a cholesterol-enriched diet

The Donryu rat is resistant to a high cholesterol diet in that typical atheromatous lesions do not develop. Using electron microscopic immunocytochemical techniques, the effects of a CCT diet (4% cholesterol with 1% cholic acid and 0.5% thiouracil) on the distributions of neuronal, macrophage, and endothelial specific nitric oxide synthase (NOS I, NOS II, and NOS III) and endothelin-1 (ET-1) immunoreactivity were examined in the thoracic aortic intima. Atheromatous lesions were absent, but immunocytochemistry showed 1. 4+/-0.52% and 4.0+/-0.9% endothelial cells (EC) with positive staining for NOS I and NOS III, respectively, compared with 16.3+/-2. 5% and 88.6+/-2.48% in control Donryu rats. The CCT-supplemented diet induced expression of NOS II immunoreactivity in thoracic aortic intimal cells. EC, subendothelial macrophages, and smooth muscle cells (SMC) also showed high NOS II-positive staining. The percentage of NOS II-immunoreactive EC was 43+/-1.8%. In control groups, no NOS II immunoreactive cells were observed. The percentage of ET-1 immunopositive cells was also significantly increased by 9. 2+/-0.66% and 64.2+/-1.4% in control and CCT-fed groups, respectively. It is concluded that the administration of a high cholesterol diet in Donryu rats produces endothelial dysfunction associated with changes in the balance of the different isoforms of NOS and ET-1. Therefore, the increase in inducible NOS and ET-1 immunoreactivity seen during the cholesterol-enriched diet appears to be a compensatory reaction of aortic wall cells to the high cholesterol supplementation.