Opposing Roles of Endothelial and Smooth Muscle Phosphatidylinositol 3-Kinase in Vasoconstriction: Effects of Rho-Kinase and Hypertension

Abstract

Phosphatidylinositol 3-kinase (PI3K) can activate endothelial nitric oxide synthase (eNOS), leading to production of the vasodilator NO. In contrast, vascular smooth muscle (VSM) PI3K may partially mediate vascular contraction, particularly during hypertension. We tested whether endothelial and VSM PI3K may have opposing functional roles in regulating vascular contraction. Secondly, we tested whether the procontractile protein rho-kinase can suppress endothelial PI3K/eNOS activity in intact arteries, thus contributing to vasoconstriction by G protein-coupled receptor (GPCR) agonists. We studied contractile responses to the GPCR agonist phenylephrine, and the receptor-independent vasoconstrictor KCl, in aortic rings from Sprague-Dawley rats. In endothelium-intact rings, the PI3K inhibitor wortmannin (0.1 M) markedly augmented responses to phenylephrine (P Ͻ 0.05) by ϳ50% but not to KCl. However, in endothelium-denuded or N G -nitro-L-arginine methyl ester (L-NAME) (100 M)-treated rings, wortmannin reduced responses to phenylephrine and KCl (P Ͻ 0.05). Furthermore, the rhokinase inhibitor Y-27632 (R-[ϩ]-trans-N-[4-pyridyl]-4-[1-aminoethyl]-cycloheaxanecarboxamide; 1 M) abolished responses to phenylephrine, and this effect was partially reversed by wortmannin or L-NAME. The ability of wortmannin to oppose the effect of rho-kinase inhibition on contractions to phenylephrine was L-NAME-sensitive. In aortas from angiotensin II-induced hypertensive rats, relaxation to acetylcholine (10 M) was impaired (P Ͻ 0.05), and vasoconstriction by phenylephrine was markedly enhanced and not further augmented by wortmannin. These data suggest that endothelial PI3K-induced NO production can modulate GPCR agonist-induced vascular contraction and that this effect is impaired in hypertension in association with endothelial dysfunction. In addition, endothelial rho-kinase may act to suppress PI3K activity and, hence, attenuate NO-mediated relaxation and augment GPCR-dependent contraction.

Segmental Differences in the Roles of Rho-Kinase and Protein Kinase C in Mediating Vasoconstriction

“…We recently reported that in aorta, where the predominant endothelium-derived relaxing factor is NO, effectiveness of rho-kinase inhibition is much greater in the presence of endothelium and, more specifically, endothelial NO synthase activity (Budzyn et al, 2005). This observation is consistent with the concept that there are several levels of interaction between rho-kinase and endothelial NO (Takemoto et al, 2002;Budzyn et al, 2004;Wolfrum et al, 2004).…”

Cold-induced cutaneous vasoconstriction is mediated by Rho kinase in vivo in human skin

“…Hodges and colleagues (19) found that full expression of cold-induced VC involves a decrease in eNOS activity and/or nitric oxide production but did not speculate as to the mechanism(s) through which localized skin cooling might regulate the eNOS pathway. Just as nitric oxide (through cyclic GMPdependent protein kinase) counters Rho kinase-mediated VC by activating myosin light chain phosphatase (7) and inhibiting activation of upstream RhoA (35), RhoA and Rho kinase similarly downregulates several steps in the eNOS pathway: decreased eNOS gene expression (30), decreased eNOS mRNA expression (13), eNOS mRNA destabilization (26,41), decreased eNOS protein expression (6,13,41), decreased activation of eNOS (6,8,30), and increased arginase activity, which decreases nitric oxide bioavailability (5,29). With a consideration for the interaction of these two systems under other conditions and in other vascular beds, it is plausible that they may interact in the cutaneous circulation during cooling, as well.…”

ANG II enhances contractile responses via PI3-kinase p110δ pathway in aortas from diabetic rats with systemic hyperinsulinemia

“…Most attention has focused on the pathways involved in cell growth and migration; however, within the last few years, PI3-K activity has been implicated in vascular smooth muscle contractility and relaxation (3,22,26,31,32). Several groups have presented evidence that links PI3-K activity and phosphatidylinositol 1,4,5-trisphosphate (PIP 3 ) production to the opening of voltage-gated and receptor-coupled Ca 2ϩ channels (25,26,38).…”