Glutamate protects against Ca 2+ paradox-induced injury and inhibits calpain activity in isolated rat hearts

Summary This study determined the effects of glutamate on the Ca2+ paradoxical heart, which is a model for Ca2+ overload-induced injury during myocardial ischemia and reperfusion, and evaluated its effect on a known mediator of injury, calpain. An isolated rat heart was retrogradely perfused in a Langendorff apparatus. Ca2+ paradox was elicited via perfusion with a Ca2+-free Krebs-Henseleit (KH) solution for 3 min followed by Ca2+-containing normal KH solution for 30 min. The Ca2+ paradoxical heart exhibited almost no viable tissue on triphenyltetrazolium chloride staining and markedly increased LDH release, caspase-3 activity, cytosolic cytochrome c content, and apoptotic index. These hearts also displayed significantly increased LVEDP and a disappearance of LVDP. Glutamate (5 and 20 mM) significantly alleviated Ca2+ paradox-induced injury. In contrast, 20 mM mannitol had no effect on Ca2+ paradox. Ca2+ paradox significantly increased the extent of the translocation of μ-calpain to the sarcolemmal membrane and the proteolysis of α-fodrin, which suggests calpain activation. Glutamate also blocked these effects. A non-selective inhibitor of glutamate transporters, DL-TBOA (10 μM), had no effect on control hearts, but it reversed glutamate-induced cardioprotection and reduction in calpain activity. Glutamate treatment significantly increased intracellular glutamate content in the Ca2+ paradoxical heart, which was also blocked by DL-TBOA. We conclude that glutamate protects the heart against Ca2+ overload-induced injury via glutamate transporters, and the inhibition of calpain activity is involved in this process. This article is protected by copyright. All rights reserved.