Altered endothelin receptor expression and affinity in spontaneously hypertensive rat cerebral and coronary arteries

Abstract

Background: Hypertension is associated with arterial hyperreactivity, and endothelin (ET) receptors are involved in vascular pathogenesis. The present study was performed to examine the hypothesis that ET receptors were altered in cerebral and coronary arteries of spontaneously hypertensive rats (SHR).

Methodology/principal findings: Cerebral and coronary arteries were removed from SHR. Vascular contraction was recorded using a sensitive myograph system. Real-time PCR and Western blotting were used to quantify mRNA and protein expression of receptors and essential MAPK pathway molecules. The results demonstrated that both ETA and ETB receptor-mediated contractile responses in SHR cerebral arteries were shifted to the left in a nonparallel manner with increased maximum contraction compared with Wistar-Kyoto (WKY) rats. In SHR coronary arteries, the ETA receptor-mediated contraction curve was shifted to the left in parallel with an increased pEC50 compared with the arteries in WKY rats. There was no significant increase in ETB receptor-mediated contraction in SHR coronary arteries. ETA receptor mRNA and protein expression was increased in SHR cerebral arteries compared with the arteries in WKY rats. However, ETA receptor mRNA and protein levels in coronary arteries and ETB receptor protein levels in cerebral and coronary arteries remained unchanged in SHR compared with WKY rats. Meanwhile, phosphorylated ERK1/2 protein was significantly increased in SHR brain and heart vessels.

Conclusions/significance: In SHR cerebral arteries, ETA receptor expression was upregulated. ETA receptor affinity was increased in coronary arteries, and ETB receptor affinity was increased in cerebral arteries. The ERK1/2 activation may be involved in the receptor alterations.

Figure 1. Concentration–response curves for cumulative sarafotoxin 6c (S6c, A and C) and endothelin-1 (ET-1, B and D) application in SHR and WKY cerebral (A, B) and coronary (C, D) arteries.

Contractile responses were demonstrated as the percentage of K⁺-induced contraction. Each data point is derived from 10–14 animals and is expressed as the mean ± SEM. Statistical analysis was performed using a two-way ANOVA. ^* P<0.05, ^** P<0.01 vs. WKY group.

Figure 2. ET_B and ET_A receptor mRNA expression levels in SHR and WKY cerebral (A) and coronary (B) arteries.

ET_B and ET_A receptor mRNA levels were expressed relative to elongation factor-1 (EF-1) levels. Each data point is derived from 7–8 animals, and the data are expressed as the mean ± SEM. Statistical analysis was performed using an unpaired Student’s t-test. ^* P<0.05 vs. WKY group.

Figure 3. ET_B and ET_A receptor protein expression levels in SHR and WKY rat cerebral (A) and coronary (B) arteries.

ET_B and ET_A receptor protein expression levels were expressed relative to β-actin levels. Each data point is derived from 7–8 animals and is expressed as the mean ± SEM. Statistical analysis was performed using an unpaired Student’s t-test. ^* P<0.05 vs. WKY group.

Figure 4. ERK1/2 protein phosphorylation in rat cerebral and coronary arteries.

Phosphorylated (p)-ERK1/2 levels in SHR group relative to the WKY group. Each data point is derived from 7–8 animals, and the data are expressed as the mean ± SEM. Statistical analysis was performed using an unpaired Student’s t-test. ^* P<0.05 vs. WKY group.