Activation of protein kinase C (PKC) and its various isoforms has been postulated to have multiple cardiovascular functions, including vascular permeability, cell migration and growth, extracellular matrix production, and expression of various cytokines. 1, 2 The ability of PKC to regulate many cardiovascular functions is not surprising, because PKC, a family of serine-threonine kinases, is an intracellular signal for many cardiovasotropic growth factors, such as angiotensin, endothelin, and vascular endothelial growth and permeability factor. 3–5 In addition, PKC activation can indirectly modulate other signal pathways, such as the Raf-MEK1–MAP kinase and PI3 kinase–Akt cascades. 6, 7

The physiological importance of PKC can also be surmised by the existence of multiple isoforms, of which 12 members have been documented to date. These are usually arranged according to their structure and substrate requirements into the following groups: conventional PKCs (cPKCs)(, 1/2, and), which are Ca2+ dependent and activated by binding to diacylglycerol (DAG) and phosphatidylserine (PS); novel PKCs (nPKCs)(,,, and), which are Ca2+ independent but are activated by DAG and PS; and atypical PKCs (aPKCs)(and/), which are Ca2+ and DAG independent but are PS sensitive. The distribution of the various PKC isoforms is tissue and species dependent. In the heart, PKC isoforms, 1/2,,, and have been identified in rat neonatal cardiomyocytes. 8 In adult rat cardiomyocytes and myocardium, PKC isoforms and seem to be maintained with age, whereas other PKC isoforms may decline. 9, 10 In human myocardium, PKC isoforms, 1/2,, and have also been reported. 11 Similarly, all PKC isoforms with the exception of PKC have been identified in the microvessels and macrovessels.