Long-term protection and mechanism of pacing-induced postconditioning in the heart

Brief periods of ventricular pacing during the early reperfusion phase (pacing-induced postconditioning, PPC) have been shown to reduce infarct size as measured after 2 h of reperfusion. In this study, we investigated (1) whether PPC leads to maintained reduction in infarct size, (2) whether abnormal mechanical load due to asynchronous activation is the trigger for PPC and (3) the signaling pathways that are involved in PPC. Rabbit hearts were subjected to 30 min of coronary occlusion in vivo, followed by 6 weeks of reperfusion. PPC consisted of ten 30-s intervals of left ventricular (LV) pacing, starting at reperfusion. PPC reduced infarct size (TTC staining) normalized to area at risk, from 49.0 ± 3.3% in control to 22.9 ± 5.7% in PPC rabbits. In isolated ejecting rabbit hearts, replacing LV pacing by biventricular pacing abolished the protective effect of PPC, whereas ten 30-s periods of high preload provided a protective effect similar to PPC. The protective effect of PPC was neither affected by the adenosine receptor blocker 8-SPT nor by the angiotensin II receptor blocker candesartan, but was abrogated by the cytoskeletal microtubule-disrupting agent colchicine. Blockers of the mitochondrial KATP channel (5HD), PKC (chelerythrine) and PI3-kinase (wortmannin) all abrogated the protection provided by PPC. In the in situ pig heart, PPC reduced infarct size from 35 ± 4 to 16 ± 12%, a protection which was abolished by the stretch-activated channel blocker gadolinium. No infarct size reduction was achieved if PPC application was delayed by 5 min or if only five pacing cycles were used. The present study indicates that (1) PPC permanently reduces myocardial injury, (2) abnormal mechanical loading is a more likely trigger for PPC than electrical stimulation or G-coupled receptor stimulation and (3) PPC may share downstream pathways with other modes of cardioprotection

Protein kinase D increases maximal Ca 2+ -activated tension of cardiomyocyte contraction by phosphorylation of cMyBP-C-Ser 315

International audienceDirkx E, Cazorla O, Schwenk RW, Lorenzen-Schmidt I, Sa-dayappan S, Van Lint J, Carrier L, van Eys GJ, Glatz JF, Luiken JJ. Protein kinase D increases maximal Ca 2ϩ-activated tension of cardiomyocyte contraction by phosphorylation of cMyBP-C-Ser 315 .Cardiac myosin-binding protein C (cMyBP-C) is involved in the regulation of cardiac myofilament contraction. Recent evidence showed that protein kinase D (PKD) is one of the kinases that phosphorylate cMyBP-C. However, the mechanism by which PKD-induced cMyBP-C phos-phorylation affects cardiac contractile responses is not known. Using immunoprecipitation, we showed that, in contracting cardiomyocytes, PKD binds to cMyBP-C and phosphorylates it at Ser 315. The effect of PKD-mediated phosphorylation of cMyBP-C on cardiac myofilament function was investigated in permeabilized ventricular myocytes, isolated from wild-type (WT) and from cMyBP-C knockout (KO) mice, incubated in the presence of full-length active PKD. In WT myocytes, PKD increased both myofilament Ca 2ϩ sensitivity (pCa50) and maximal Ca 2ϩ-activated tension of contraction (Tmax). In cMyBP-C KO skinned myocytes, PKD increased pCa50 but did not alter Tmax. This suggests that cMyBP-C is not involved in PKD-mediated sensitization of myofilaments to Ca 2ϩ but is essential for PKD-induced increase in Tmax. Furthermore, the phosphorylation of both PKD-Ser 916 and cMyBP-C-Ser 315 was contraction frequency-dependent, suggesting that PKD-mediated cMyBP-C phosphorylation is operational primarily during periods of increased contractile activity. Thus, during high contraction frequency, PKD facilitates contraction of cardiomyocytes by increasing Ca 2ϩ sensitivity and by an increased Tmax through phosphorylation of cMyBP-C. cardiomyocyte contractility; calcium sensitivity; protein kinase A; phospho-cardiac myosin-binding protein C-serine-31