095P Brighton
Winter Meeting December 2007 |
Pharmacological evidence for two new post-receptor mechanisms, SERCA and BKCa activation, in B-type natriuretic peptide protection of reperfused myocardium
Dwaine Burley, Gary Baxter
Cardiff University, Cardiff, United Kingdom
B-type natriuretic peptide (BNP) given at the time of reperfusion, is protective in different experimental models of myocardial reperfusion injury. Our recent studies examining the endogenous components of this protection, have explored KATP channel activation (Burley & Baxter, 2007), but no studies have focused on the sarcoplasmic reticulum Ca2+-ATPase (SERCA), or the large conductance K+ (BKCa) channel. We hypothesised that BNP induced protection of reperfused myocardium, involves SERCA and BKCa channel activation.
Male Sprague-Dawley rats (270-350g) were anaesthetised with sodium pentobarbital (65 mg/kg). Hearts were then Langendorff perfused with modified Krebs-Henseleit buffer. After stabilisation, hearts were subjected to 35 min coronary artery occlusion, followed by 120 min reperfusion. Drugs were administered from last 5 min of occlusion, until 10 min into reperfusion. Infarct size was measured as percentage of ischaemic risk zone, using triphenyltetrazolium staining. In study 1, hearts were treated with BNP 10 nM, and the SERCA inhibitors, thapsigargin 150 nM and cyclopiazonic acid 100 nM. In study 2, hearts were treated with BNP 10 nM, the BKCa channel inhibitor paxilline 1 μM, and the BKCa channel activator NS1619 30 μM (1,3-dihydro-1-[2-hydroxy-5-(trifluoromethyl)phenyl]-5-(trifluoromethyl)-2H-benzimidazol-2-one).
| Study 1 (n = 4-12) |
Infarct size |
Study 2 (n = 5-10) |
Infarct size |
| Control |
39.5 ± 2.3% |
Control |
41.4 ± 2.6% |
| BNP |
23.8 ± 3.9%** |
BNP |
16.1 ± 2.4%** |
| Thapsigargin |
38.9 ± 3.1% |
Paxilline |
39.4 ± 3.6% |
| BNP + Thapsigargin |
43.7 ± 1.9%## |
BNP + Paxilline |
45.6 ± 3.0%## |
| Cyclopiazonic acid |
38.6 ± 4.8% |
NS1619 |
22.4 ± 5.5%* |
| BNP + Cyclopiazonic acid |
43.6 ± 4.3%## |
|
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*P<0.05, **P<0.01 vs. control; ##P<0.01 vs. BNP. (1-way ANOVA + Newman-Keuls test) mean ± SEM
In study 1, BNP at reperfusion caused a significant reduction in infarct size. This protection was aborted by thapsigargin and cyclopiazonic acid, implicating the activation of SERCA as a key component of BNP protection at reperfusion. In study 2, protection afforded by BNP at reperfusion, and this protection was abrogated by paxilline, whereas NS1619 given at reperfusion induced protection in similar fashion to BNP. These findings provide pharmacological evidence for two new post-receptor mechanisms, SERCA and BKCa activation, which are involved in BNP’s protection of reperfused myocardium.
Burley DS, Baxter GF (2007). Basic Res Cardiol (in press)
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