Post-conditioning restores pre-ischaemic receptor coupling in rat isolated hearts

Area of Science:

• Cardiology
• Molecular Biology
• Physiology

Background:

• Ischaemic preconditioning (IPC) and ischaemic post-conditioning (IPoC) are protective strategies against myocardial infarction.
• These conditioning methods activate signaling pathways, including phosphatidylinositol (PI) 3-kinase, involved in receptor desensitization and resensitization.
• IPC and IPoC may influence receptor coupling after infarction, impacting cardiac function recovery.

Purpose of the Study:

• To investigate the effects of IPC and IPoC on post-infarct receptor coupling.
• To determine the role of PI 3-kinase and protein kinase C in the protective effects of IPC and IPoC.
• To assess the impact of IPC and IPoC on the responsiveness of parathyroid hormone-related peptide (PTHrP) and beta-adrenoceptors.

Main Methods:

• Rat isolated hearts underwent 45 minutes of flow arrest followed by 120 minutes of reperfusion, with or without IPC or IPoC.
• Left ventricular developed pressure (LVdevP) was measured to assess cardiac function.
• Receptor responsiveness was monitored by exposing hearts to PTHrP or isoprenaline after reperfusion.
• Reperfusion injury was quantified by enzyme release.

Main Results:

• IPC and IPoC significantly reduced enzyme release, indicating reduced reperfusion injury.
• IPoC restored normal PTHrP receptor responsiveness, characterized by negative inotropism, which was impaired by ischaemia alone.
• PI 3-kinase inhibition (wortmannin) attenuated the protective and resensitizing effects of IPoC.
• IPoC also restored beta-adrenoceptor responsiveness.

Conclusions:

• IPoC restores PTHrP receptor coupling in a PI 3-kinase-dependent manner.
• These findings suggest that IPoC can improve post-infarct cardiac function by restoring receptor responsiveness.
• A similar PI 3-kinase-dependent mechanism may underlie beta-adrenoceptor resensitization after ischaemia.