Activated Protein Kinase C Attenuates Ca2+ Overloading and Reoxygenation Hypercontracture in Isolated Rat Cardiomyocytes following Chemical Hypoxia

The aims of this study were i) to test the effects of protein kinase C (PKC) activation on the intracellular Ca2+ concentration of rat cardiomyocytes during chemical hypoxia-reoxygenation, ii) to determine the contribution of the sarcoplasmic reticulum (SR) and the Na+-Ca2+ exchange on the regulation of intracellular Ca2+ following PKC activation and iii) to test the role of PKC-dependent intracellular pH changes in intracellular Ca2+ regulation. We used the isolated adult rat cardiomyocyte perfusion model. Cardiomyocytes were loaded with the Ca2+-fluorescent probe Fluo-3 and the pH-fluorescent probe SNARF1. Cells were subjected to 50 min of glucose-free and NaCN chemical hypoxia followed by 30 min of simulated reoxygenation. The activation of PKC significantly inhibited the hypoxia-induced increase of Fluo-3 fluorescent intensity (control; 692 ± 100% and activated PKC; 322 ± 43%: P < 0.05). This inhibitory effect was not affected by the inhibition of the SR Ca2+ uptake induced by thapsigargin, but was cancelled by the inhibition of the Na+-Ca2+ exchange with dichlorobenzamil (thapsigargin 337 ± 47%; dichlorobenzamil 609 ± 100%). PKC activation also attenuated the decrease in intracellular pH during chemical hypoxia, even in the presence of the Na+-H+ exchange inhibitor amiloride (control; 6.54 ± 0.02, PKC; 6.72 ± 0.03, PKC + amiloride; 6.73 ± 0.03). We concluded that the PKC attenuation of Ca2+ overloading to rat cardiomyocytes during chemical hypoxia-reoxygenation does not depend on the Ca2+ uptake by the SR, but does require a Na+-Ca2+ exchange. Since PKC attenuated the increasing intracellular H+ during chemical hypoxia, a low H+ concentration may be important for the maintenance of Ca2+ extrusion via the Na+-Ca2+ exchange.