Abstract P125: Long-term Exposure Of Angiotensin II Enhanced Vascular Contraction Via Activation Of Protein Kinase C Beta

Protein kinase C (PKC) β is linked to lymphoma and diabetes complications including diabetic retinopathy, nephropathy and neuropathy. Also, recent studies revealed that PKCβ activation also accelerates atherosclerotic plaque formation in diabetes. These findings strongly indicate that PKCβ is a potential target for the treatment of diabetic vascular complications. Although PKCβ is associated with diabetic vascular dysfunction, role of PKCβ in hypertension remains unclear. Since hypertension is one of most important risk factor for vascular diseases including atherosclerosis, we here examined whether PKCβ is involved in angiotensin II-induced vascular dysfunction. Treatment with angiotensin II (100 nM) for 30 min strongly increased phosphorylation at the PKCβ activation site at S660 in aorta from Wistar rat (n=4). Treatment of rat aorta with angiotensin II (100 nM) for 24 hr increased contractile responses to serotonin (5-HT, Maximum contraction, control vs. Angiotensin II, 92.2±20.0 vs 142.1±20.5%, P<0.05, n=6) or endothelin-1 (ET-1, 157.4±30.6 vs 214.1±24.3%, P<0.05, n=8). In contrast, angiotensin II did not affect vascular contractile response to noradrenaline (n=4). The enhanced contraction induced by angiotensin II was blocked by CGP53353 (1 μM), a PKCβ inhibitor (5-HT, Angiotensin II vs. CGP53353+Angiotensin II,197.8±27.8 vs. 167.4±17.6%, P<0.05, n=4-5). Pretreatment with LY333531 (1 μM), another PKCβ inhibitor, also prevented angiotensin II-induced vascular dysfunction (P<0.05, n=3-4). Next, we generated PKCβ knockout rat using rGONAD. Consistent with the results using PKCβ inhibitors, angiotensin II-induced enhanced contractile responses to 5-HT (122.6±15.6 vs 111.0±16.3%, n=4) and ET-1 (137.9±39.9 vs 139.2±30.1%, n=4) were dismissed in PKCβ knockout rat. We also confirmed that phorbol12-myristate13-acetate (0.05-5 μg/ml), a PKC activator, enhanced vascular contractile responses to 5-HT and ET-1 in dose-dependent manner (P<0.05, n=4). We conclude that long exposure of angiotensin II (24 hr) causes increase in vascular contractile responses to 5-HT and ET-1 and the augmented contraction are due to activation of PKCβ. Our result suggests that PKCβ might be associated with angiotensin II-related vascular dysfunction.