Phosphoinositide 3-Kinase Mediates Enhanced Spontaneous and Agonist-Induced Contraction in Aorta of Deoxycorticosterone Acetate-Salt Hypertensive Rats

Abstract

Abstract-Arteries from deoxycorticosterone acetate (DOCA)-salt and N -nitro-L-arginine (L-NNA) hypertensive but not normotensive rats develop spontaneous tone. LY294002 and wortmannin, phosphoinositide 3-kinase (PI3-kinase) inhibitors, eliminate spontaneous tone. We hypothesized that PI3-kinase protein and/or activity was increased in hypertension and contributed to the observed enhanced contractility. PI3-kinase activity assays revealed 2-fold higher activity in thoracic aorta from DOCA-salt [systolic blood pressure (SBP)ϭ184Ϯ5 mm Hg] compared with sham rats (SBPϭ111Ϯ2 mm Hg). Western analyses of aortic homogenates revealed the presence of p85␣, p110␣, p110␤, and p110␦ but not p110␥ PI3-kinase subunits; p110␦ protein was elevated in aorta of hypertensive rats as compared with sham. Aortic homogenates from L-NNA rats also had elevated p110␤ protein density, but neither L-NNA nor DOCA-salt had differences in p85␣ and p110␣. Total Akt density was unaltered, but pAkt was significantly lower in homogenates from DOCA-salt rats. LY294002 (20 mol/L) and nifedipine (50 nmol/L) abolished Ca 2ϩ -induced spontaneous tone in aorta from DOCA-salt rats. However, LY294002 did not alter BayK8644-induced contraction, indicating that LY294002 does not inhibit L-type Ca 2ϩ channels directly. PTEN (phosphatase and tensin homolog) and pPTEN were expressed but not different in aorta from DOCA-salt and sham rats. LY294002 corrected the enhanced contraction to KCl and norepinephrine in aorta from DOCA-salt rats. These data support an increase in PI3-kinase activity and p110␦ density in aorta from L-NNA and DOCA-salt rats. Importantly, this increase contributes to the enhanced contractility observed in two models of hypertension. Key Words: phosphoinositide 3-kinase Ⅲ artery Ⅲ deoxycorticosterone acetate-salt hypertension Ⅲ phosphatase and tensin homolog Ⅲ N -nitro-L-arginine hypertension P hosphoinositide 3-kinase (PI3-kinase) is a multifaceted enzyme, possessing both lipid and protein kinase activity. It participates in multiple signaling pathways, receiving input from a variety of receptors ultimately leading to changes in gene expression, metabolism, cell division, apoptosis, cellular trafficking, and contractility.

The PI3-K/Akt pathway: roles related to alterations in vasomotor responses in diabetic models

“…PI3-K reduces force in vascular smooth muscle in response to either membrane depolarization or receptor activation (Komalavilas et al, 2001;Northcott et al, 2002;Su et al, 2004). Indeed, Su and colleagues suggested that PI3-K performs at least two distinct roles in the regulation and/or modulation of force (Su et al, 2004).…”

“…The second major pathway is potentially protein kinase Cdependent, and enhances force independently of changes in either Ca 2+ or myosin light chain (MLC) phosphorylation levels. PI3-K has also been implicated in the pathology of hypertensioninduced vascular hypersensitivity and ethanol-induced cerebral contractions (Yang et al, 2001;Northcott et al, 2002). Watts and coworkers reported that an enhancement of PI3-K activation seems to underlie the increase in spontaneous vascular tone observed in both deoxycorticosterone acetate (DOCA)-salt and N-nitro-L-Arg hypertensive rats (Northcott et al, 2002.…”

“…PI3-K has also been implicated in the pathology of hypertensioninduced vascular hypersensitivity and ethanol-induced cerebral contractions (Yang et al, 2001;Northcott et al, 2002). Watts and coworkers reported that an enhancement of PI3-K activation seems to underlie the increase in spontaneous vascular tone observed in both deoxycorticosterone acetate (DOCA)-salt and N-nitro-L-Arg hypertensive rats (Northcott et al, 2002. They noted that a specific inhibitor of p110δ, IC87114, inhibited the spontaneous aortic tone observed in DOCA-salt rats in a concentration-dependent manner.…”

“…PI3-K subsequently phosphorylates Akt, which in turn phosphorylates NOS, and thereby increases NO production. Concerning vascular smooth muscle cells, several groups have presented evidence to link PI3-K activity and phosphatidylinositol -3,4,5-trisphosphate (PIP3) production to the opening of voltage-gated and receptor-coupled calcium channels (Macrez et al, 2001;Northcott et al, 2002;Su et al, 2004). Further, it has been suggested that norepinephrine (NE) and angiotensin II (Ang II), as activators of G-proteincoupled receptors, exhibit cross-talk with PI3-K activity in human vascular smooth muscle cells (Hu et al, 1996;Hafizi et al, 2004).…”

PI3-Kinase Upregulation and Involvement in Spontaneous Tone in Arteries From DOCA-Salt Rats

“…7 Moreover, Class IA regulatory p85␣ subunit-associated PI3-kinase activity and PI3-kinase protein expression, specifically the p110␦ subunit, was upregulated in aorta from DOCA-salt hypertensive rats compared with normotensive sham animals. 7 It is not apparent how different p110 isoforms play specific functional roles in cells. Moreover, the aorta, a conduit artery, is the tissue in which most of the characterization of PI3-kinase and hypertension has been studied and only has a relatively small influence on blood pressure.…”