Protection of rat cardiomyocytes against simulated ischemia and reoxygenation by treatment with protein kinase C activator.

The aim of this study was to investigate whether treatment with the protein kinase C (PKC) agonist 1,2-dioctanoyl-sn-glycerol (1,2DOG) can protect isolated adult Wistar rat cardiomyocytes against simulated ischemia and reoxygenation. Cytosolic Ca2+ (assessed by fura 2 fluorescence), pHi (assessed by BCECF fluorescence), and cell length were measured during 80 minutes of simulated ischemia (anoxia, pHo 6.4) and 20 minutes of reoxygenation (pHo 7.4) and compared between control cells and cells treated with 20 micromol/L 1,2DOG before anoxia (10-minute treatment and 10-minute washout), before and during anoxia (two-step treatment), or only during anoxia. Treatment before anoxia attenuated rigor contracture but did not influence anoxic Ca2+ overload. In contrast, two-step treatment before and during anoxia accelerated rigor contracture but reduced the rate of anoxic Ca2+ accumulation. During reoxygenation, control cells developed irreversible hypercontracture (reduction of cell length to 43+/-2% of the initial cell length, n=62), which was accompanied by spontaneous oscillations of cytosolic Ca2+ (19.6+/-1.6 per minute). Two-step treatment with 1,2DOG before and during anoxia significantly reduced hypercontracture (reduction of cell length to 60+/-2%, P<.01 versus control, n=41) and suppressed spontaneous Ca2+ oscillations (2.8+/-0.9 per minute, P<.01 versus control). These effects could not be reproduced by treatment with 1,2DOG before anoxia or during anoxia or by a two-step treatment with the PKC-inactive 1,3-dioctanoyl-sn-glycerol and were fully abolished with 1 micromol/L bisindolylmaleimide (PKC inhibitor). We conclude that a two-step activation of PKC before and during anoxia is required for effective protection of cardiomyocytes against anoxic Ca2+ overload and reoxygenation-induced hypercontracture.