Two Distinct Mechanisms Mediate a Differential Regulation of Protein Kinase C Isozymes in Acute and Prolonged Myocardial Ischemia

Abstract

An activation of protein kinase C (PKC) in acute myocardial ischemia has been shown previously using its translocation to the plasma membrane as an indirect parameter. However, whether PKC remains activated or whether other mechanisms such as altered gene expression may mediate an isozyme-specific regulation in prolonged ischemia have not been investigated. In isolated perfused rat hearts, PKC activity and the expression of PKC cardiac isozymes were determined on the protein level using enzyme activities and Western blot analyses and on the mRNA level using reverse transcriptase-polymerase chain reaction after various periods of global ischemia (1 to 60 minutes). As early as 1 minute after the onset of ischemia, PKC activity is translocated from the cytosol to the particulate fraction without change in total cardiac enzyme activity. This translocation involves all major cardiac isozymes of PKC (ie, PKCalpha, PKCdelta, PKCepsilon, and PKCzeta). This rapid, nonselective activation of PKCs is only transient. In contrast, prolonged ischemia (>/=15 minutes) leads to an increased cardiac PKC activity (119+/-7 versus 190+/-8 pmol/min per mg protein) residing in the cytosol. This is associated with an augmented, subtype-selective isozyme expression of PKCdelta and PKCvarepsilon (163% and 199%, respectively). The specific mRNAs for PKCdelta (948+/-83 versus 1501+/-138 ag/ng total RNA, 30 minutes of ischemia) and PKCepsilon (1597+/-166 versus 2611+/-252 ag/ng total RNA) are selectively increased. PKCalpha and PKCzeta remain unaltered. In conclusion, two distinct activation and regulation processes of PKC are characterized in acute myocardial ischemia. The early, but transient, translocation involves all constitutively expressed cardiac isozymes of PKC, whereas in prolonged ischemia an increased total PKC activity is associated with an isozyme-selective induction of PKCepsilon and PKCdelta. Whether these fundamentally different activation processes interact remains to be elucidated.

Activation of Protein Kinases in Chronically Hypoxic Infant Human and Rabbit Hearts

“…12 Changes in specific PKC isoforms located in the myocardium have been reported, particularly in ischemic preconditioning, ischemia-reperfusion, heart failure caused by cardiomyopathy, and diabetes. 7,[13][14][15] Our studies indicate activation of PKC⑀ is an important adaptive response to chronic hypoxia.…”

Activation of ɛ protein kinase C correlates with a cardioprotective effect of regular ethanol consumption

“…Studies in animal and human myocardium demonstrate that cardioprotection by ischemic preconditioning is abolished by PKC inhibitors given prior to ischemia-reperfusion (21)(22)(23)45), mimicked by PKC activators (22,23), and that membrane PKC activity is enhanced during ischemia, suggesting PKC translocation (24,46). Recent reports correlate activation of specific PKC isozymes, including , ␦ and ␣PKC, with ischemic preconditioning (26-29).…”

Regulation of membrane-associated iPLA2 activity by a novel PKC isoform in ventricular myocytes

“…Alterations in specific myocardial PKC isoform activity have been reported previously, particularly in ischemic preconditioning (6,15,27), ischemiareperfusion (1,28), heart failure resulting from cardiomyopathy (3), and diabetes (11). The exact PKC isoforms that are preferentially activated in these conditions have been difficult to determine; however, PKC-⑀ and PKC-␦ are important for ischemic preconditioning, and PKC-␣ and PKC-␤ 1/2 are activated in heart failure associated with diabetes or nonviral cardiomyopathy.…”