IngentaConnect Upregulated function of phosphatidylinositol-3-kinase in genetica...

Abstract:

SUMMARY

1. The growth enzyme phosphatidylinositol 3-kinase (PI3K) was recently implicated in the mediation of arterial spontaneous tone, an event observed in arteries from hypertensive, but not normotensive, subjects that contributes to changes in total peripheral resistance in the hypertensive state. We have shown this occurrence in experimentally induced models of hypertension. However, because the majority of hypertension is genetically based, it is important to demonstrate a similar change in genetically hypertensive animals.

2. Aorta from spontaneously hypertensive rats (SHR; systolic blood pressure = 183 ± 4 mmHg) and Wistar Kyoto (WKY) rats (115 ± 2 mmHg) were isolated for the measurement of isometric contractile force. Aorta from SHR displayed small increases (approximately 5% maximum phenylephrine (PE)-induced contraction) in spontaneous tone, whereas aorta from WKY rats displayed none. The non-selective PI3K inhibitor LY294002 (20 µmol/L) and the selective inhibitor of the p110 dgr

catalytic subunit of PI3K IC87114 (20 µmol/L) caused a fall of basal tone in SHR aorta (20 ± 7 and 24 ± 6% of the initial PE contraction, respectively), but did not alter tone in arteries from WKY rats. LY294002, but not IC87114, normalized the increased potency of noradrenaline (NA) observed in aorta from SHR (–log EC₅₀ values for NA in the presence of vehicle in WKY rats and SHR 7.5 ± 0.1 and 7.8 ± 0.1, respectively (P < 0.05); –log EC₅₀ values for NA in the presence of LY294002 in WKY rats and SHR 7.0 ± 0.1 and 7.0 ± 0.1, respectively).

3. Biochemical expression of the p110 catalytic and p85 regulator subunits of PI3K in western analyses revealed no difference in expression of the regulatory p85 agr

or p110

protein subunits between WKY rats and SHR; p110 ggr

was not detected. In contrast, p110 dgr

expression was increased greater than 30% in aorta from SHR compared with WKY rats (827.6 ± 88.5 vs 576.8 ± 53.4 arbitrary densitometry units, respectively). Immunohistochemical analyses revealed expression of the p110 dgr

isoform in the smooth muscle of arteries.

4. These data underscore the relevance of an enzyme historically classified as one committed to growth/anti-apoptosis in modifying contractility and supports involvement of PI3K in genetically based hypertension.

Keywords: artery; genetic hypertension; phosphatidylinositol 3-kinase; spontaneous tone

Document Type: Original article

DOI: 10.1111/j.1440-1681.2010.04276.x

Affiliations: 1: Department of Pharmacology and Toxicology, Michigan State University, East Lansing, Michigan and 2: ICOS Co., Seattle, Washington, USA

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Upregulated function of phosphatidylinositol-3-kinase in genetically hypertensive rats: a moderator of arterial hypercontractility