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Thromboxane-induced contractile response of human coronary arterioles is diminished after cardioplegic arrest
Jun Feng1, Yuhong Liu, Louis M Chu
1Division of Cardiothoracic Surgery, Cardiovascular Research Center, Rhode Island Hospital, Alpert Medical School of Brown University, Providence, Rhode Island 02903, USA.
Insights
Cardioplegia and reperfusion impair human coronary arteriole contraction to thromboxane A-2 (TXA-2). This response involves TXA-2 receptors and phospholipase-C (PLC), but not protein kinase C-alpha (PKC-α).
Area of Science:
- Cardiovascular Physiology
- Vascular Biology
- Cardiac Surgery
Background:
- Investigated human coronary microvasculature contractile response to thromboxane A-2 (TXA-2).
- Examined effects of TXA-2 receptor blockade and inhibition of phospholipase-C (PLC) or protein kinase C-alpha (PKC-α).
- Assessed changes before and after cardioplegia with reperfusion (CP/Rep), including protein/gene expression and localization of key proteins.
Purpose of the Study:
- To determine the impact of cardioplegia/reperfusion on human coronary arteriole contractility.
- To elucidate the signaling pathways (TXA-2 receptors, PLC, PKC-α) involved in TXA-2-mediated contraction post-CP/Rep.
Main Methods:
- Harvested human right atrial tissue before and after CP/Rep from cardiac surgery patients.
- Isolated and dissected coronary arterioles (90-170 µm diameter).
- Assessed contractile responses to TXA-2 analog (U-46619) with and without receptor antagonists and enzyme inhibitors (SQ-29548, U73122, safingol).
- Analyzed protein and gene expression of TXA-2 receptors, TXA-2 synthase, and PLC isoforms using Western blot and RT-PCR.
- Utilized confocal microscopy for protein localization.
Main Results:
- Post-CP/Rep contractile response to U-46619 was significantly impaired compared to pre-CP/Rep.
- TXA-2 receptor antagonist (SQ-29548) and PLC inhibitor (U73122) blocked U-46619-induced contraction.
- PKC-α inhibitor (safingol) did not affect contraction.
- Protein and gene expression levels of TXA-2 receptors, TXA-2 synthase, and PLC isoforms remained unchanged post-CP/Rep.
- Confocal microscopy revealed no significant differences in TXA-2 receptor or PLC-β3 expression; both proteins were found in smooth muscle and endothelium.
Conclusions:
- Cardioplegia/reperfusion significantly reduces the contractile function of human coronary arterioles in response to TXA-2.
- The contractile mechanism involves the activation of TXA-2 receptors and phospholipase-C (PLC).
- PKC-α does not appear to play a significant role in this specific contractile pathway after CP/Rep.
Background:
We investigated the contractile response of human coronary microvasculature to thromboxane A-2 (TXA-2), with and without the blockade of TXA-2 receptors or the inhibition of phospholipase-C (PLC) or of protein kinase C-α (PKC-α) in the human coronary microvasculature before and after cardioplegia, followed by reperfusion (CP/Rep). Protein/gene expression and localization of TXA-2 receptors, TXA-2 synthase, PLC, and other TXA-2-related proteins was also examined.
Methods:
Right atrial tissue was harvested before and after cold blood cardioplegia, followed by about 10 minutes of reperfusion, from 28 patients undergoing cardiac operations. Coronary arterioles (90 to 170 microm in diameter) were dissected from the harvested tissue.
Results:
The post-CP/Rep contractile response of coronary arterioles to TXA-2 analog U-46619 was significantly impaired vs pre-CP/Rep (p<0.05). The TXA-2 receptor antagonist SQ-29548 (10(-6) M) prevented the contractile response to U-46619 (p<0.05). Pretreatment with the PLC inhibitor U73122 (10(-6) M) significantly inhibited the U-46619-induced contractile response (p<0.05). Administration of the PKC-α inhibitor safingol failed to affect U-46619-induced contraction. Total protein levels and gene expression of TXA-2 receptors, TXA-2 synthase, PLC-β3, phospho-PLC-β3, PLC-γ1, and phospho-PLC-γ1 were not altered after CP/Rep. Confocal microscopy showed no significant differences in the expression of TXA-2 receptors or PLC-β3 in the microcirculation. TXA-2 receptors and PLC-β3 were both present in smooth muscle and endothelium.
Conclusions:
Cardioplegia/Rep decreases the contractile response of human coronary arterioles to TXA-2 soon after cardiac operations. The contractile response to the TXA-2 analog U-46619 is through activation of TXA-2 receptors and PLC.
