Protection of ischemic myocardium in diabetics by inhibition of electroneutral Na+-K+-2Cl(-) cotransporter

Diabetes increases both the incidence of cardiovascular disease and complic ations of myocardial infarction and heart failure. Studies using diabetic a nimals have shown that changes in myocardial sodium transporters result in alterations in intracellular sodium (Na-i) homeostasis. Because the changes in sodium homeostasis can be due to increased entry of Na+ via the electro neutral Na+-K+-2Cl(-) cotransporter (NKCC), we conducted experiments in acu te diabetic hearts to determine if 1) net inward cation flux via NKCC is in creased, 2) this cotransporter contributes to a greater increase in Nai dur ing ischemia, and 3) inhibition of NKCC limits injury and improves function after ischemia-reperfusion. These issues were investigated in perfused typ e I diabetic and nondiabetic rat hearts subjected to ischemia and 60 min of reperfusion. A group of diabetic and nondiabetic hearts was perfused with 5 muM of bumetanide, an inhibitor of NKCC. Flux via NKCC, Nai, and ATP was measured in each group with the use of radiotracer Rb-86, Na-23, and P-31 n uclear magnetic resonance spectroscopy, respectively, whereas ischemic inju ry was assessed by measuring creatine kinase release on reperfusion. Cation flux via NKCC, as measured by Rb-86 uptake, was significantly increased in diabetic hearts. Inhibition of NKCC significantly reduced ischemic injury in diabetic hearts, improved functional recovery on reperfusion, attenuated the ischemic rise in Na-i, and conserved ATP during ischemia-reperfusion. Parallel studies in nondiabetic hearts showed that NKCC inhibition was not cardioprotective. These findings demonstrate that flux via NKCC is increase d in type I diabetic hearts and that inhibition with bumetanide attenuates changes in Na-i and ATP during ischemia and protects against ischemic injur y. The data suggest a therapeutic role for pharmacological agents that inhi bit flux via NKCC in diabetic patients with myocardial ischemia.