A dual mechanism of cytoprotection afforded by M-LDH in embryonic heart H9C2 cells

Muscle form of lactate dehydrogenase (M-LDH), a minor LDH form in cardiomyocytes, physically interacts with ATP-sensitive K(+) (K(ATP)) channel-forming subunits. Here, we have shown that expression of 193gly-M-LDH, an inactive mutant of M-LDH, inhibit regulation of the K(ATP) channels activity by LDH substrates in embryonic rat heart H9C2 cells. In cells expressing 193gly-M-LDH chemical hypoxia has failed to activate K(ATP) channels. The similar results were obtained in H9C2 cells expressing Kir6.2AFA, a mutant form of Kir6.2 with largely decreased K(+) conductance. Kir6.2AFA has slightly, but significantly, reduced cellular survival under chemical hypoxia while the deleterious effect of 193gly-M-LDH was significantly more pronounced. The levels of total and subsarcolemmal ATP in H9C2 cells were not affected by Kir6.2AFA, but the expression of 193gly-M-LDH led to lower levels of subsarcolemmal ATP during chemical hypoxia. We conclude that M-LDH regulates both the channel activity and the levels of subsarcolemmal ATP and that both mechanism contribute to the M-LDH-mediated cytoprotection.