Mechanisms of Myocardial Protection by Adenosine-Supplemented Cardioplegia: Differential Response of Calcium-Independent Protein Kinase C Isozymes

Abstract Background. Adenosine-supplemented cardioplegia improves myocardial function after cardioplegic arrest. However, the underlying cellular mechanism(s) responsible for adenosine's protective actions remains unclear. We tested the hypothesis that protection by adenosine-supplemented cardioplegia would be associated with selective activation of protein kinase C (PKC) isozymes δ and ϵ. Materials and methods. Isolated rat hearts were perfused (37°C, Krebs–Ringer bicarbonate buffer) for 30 min, after which baseline functional measurements were made. This was followed by 120 min of cold cardioplegic arrest at 4°C with either St. Thomas No. 2 (ST#2), ST#2 + adenosine (100 μM, ADO) or ST#2 + ADO + 8-sulfophenyltheophylline (50 μM, SPT). Hearts were reperfused for 60 min and functional measurements made. Distribution of PKC isoforms was determined (immunoblotting) after 30 min of warm perfusion (No-CDPL) or after 30 min of perfusion followed by 15 min of cardioplegic arrest. Results. ADO prevented myocardial dysfunction after cardioplegic arrest. PKC-δ did not differ in the cytosolic fraction among groups. However, ADO prevented increases in particulate fraction PKC-δ, but elicited a significant increase in the particulate fraction PKC-ϵ, while ST#2 or SPT significantly decreased the cytosolic fraction PKC-ϵ. Both functional and cellular changes associated with ADO were receptor mediated. Conclusion. This novel, dual action of adenosine-supplemented cardioplegia on PKC isoforms may be responsible for the associated functional improvements.