Two distinct mechanisms mediate a differential regulation of protein kinase C isozymes in acute and prolonged myocardial ischemia

An activation of protein kinase C (PKC) in acute myocardial ischemia has be en shown previously using its translocation to the plasma membrane as an in direct parameter. However, whether PKC remains activated or whether other m echanisms such as altered gene expression may mediate an isozyme-specific r egulation in prolonged ischemia have not been investigated. In isolated per fused rat hearts, PKC activity and the expression of PKC cardiac isozymes w ere determined on the protein level using enzyme activities and Western blo t analyses and on the mRNA level using reverse transcriptase-polymerase cha in 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 cardi ac enzyme activity. This translocation involves all major cardiac isozymes of PKC tie, PKC alpha, PKC delta, PKC epsilon, and PKC zeta. This rapid, no nselective activation of PKCs is only transient. In contrast, prolonged isc hemia (greater than or equal to 15 minutes) leads to an increased cardiac P KC activity (119+/-7 versus 190+/-8 pmol/min per mg protein) residing in th e cytosol. This is associated with an augmented, subtype-selective isozyme expression of PKC delta and PKC epsilon (163% and 199%, respectively). The specific mRNAs for PKC delta (948+/-83 versus 1501+/-138 ag/ng total RNA, 3 0 minutes of ischemia) and PKCE (1597+/-166 versus 2611+/-252 ag/ng total R NA) are selectively increased. PKC alpha and PKC zeta remain unaltered. In conclusion, two distinct activation and regulation processes of PKC are cha racterized in acute myocardial ischemia. The early, but transient, transloc ation involves all constitutively expressed cardiac isozymes of PKC, wherea s in prolonged ischemia an increased total PKC activity is associated with an isozyme-selective induction of PKC epsilon and PKC delta. Whether these fundamentally different activation processes interact remains to be elucida ted.