No flow ischemia inhibits insulin signaling in the heart by decreasing intracellular pH

Abstract

Abstract-Glucose-insulin-potassium solutions exert beneficial effects on the ischemic heart by reducing infarct size and mortality and improving postischemic left ventricular function. Insulin could be the critical protective component of this mixture, although the insulin response of the ischemic and postischemic myocardium has not been systematically investigated. The aim of this work was to study the insulin response during ischemia by analyzing insulin signaling. This was evaluated by measuring changes in activity and/or phosphorylation state of insulin signaling elements in isolated perfused rat hearts submitted to no-flow ischemia. Intracellular pH (pH i ) was measured by NMR. No-flow ischemia antagonized insulin signaling including insulin receptor, insulin receptor substrate-1, phosphatidylinositol 3-kinase, protein kinase B, p70 ribosomal S6 kinase, and glycogen synthase kinase-3. These changes were concomitant with intracellular acidosis. Perfusing hearts with ouabain and amiloride in normoxic conditions decreased pH i and insulin signaling, whereas perfusing at pH 8.2 counteracted the drop in pH i and the inhibition of insulin signaling by ischemia. Incubation of cardiomyocytes in normoxic conditions, but at pH values below 6.75, mimicked the effect of ischemia and also inhibited insulin-stimulated glucose uptake. Finally, the in vitro insulin receptor tyrosine kinase activity was progressively inhibited at pH values below physiological pH i , being abolished at pH 6.0. Therefore, ischemic acidosis decreases kinase activity and tyrosine phosphorylation of the insulin receptor thereby preventing activation of the downstream components of the signaling pathway. We conclude that severe ischemia inhibits insulin signaling by decreasing pH i . (Circ Res. 2001;88:513-519.)

Inhibition of the mTOR/p70S6K pathway is not involved in the insulin-sensitizing effect of AMPK on cardiac glucose uptake

“…2A). In agreement with previous data obtained in perfused hearts and cardiomyocytes in suspension (2,16), no p70S6K phosphorylation could be detected in untreated cells and AMPK activation by phenformin had no effect under these basal conditions ( Fig. 2A).…”

“…In addition, PKB/Akt induces the phosphorylation and activation of the mammalian target of rapamycin (mTOR)/p70S6K pathway, which, then, phosphorylates IRS-1 on serine residues leading to the inhibition of the insulin signaling (2). AMPK phosphorylates and inhibits AS160 stimulating glucose uptake independently of insulin (3).…”

GSK-3β inhibition protects mesothelial cells during experimental peritoneal dialysis through upregulation of the heat shock response

“…Data on the association of acidosis and GSK-3β are scarce. However, Beauloye et al also reported that insulin (a classical inhibitor of GSK-3β) (Grimes and Jope 2001) does not decrease GSK-3β activity in an acidotic intracellular environment, suggesting that low pH might indeed result in a higher propensity for GSK-3β activation (Beauloye et al 2001). The role of GSK-3β as a potential drug target has become more and more prominent in the last years (Phukan et al 2010).…”

Impact of High Glucose/High Insulin and Dichloroacetate Treatment on Carbohydrate Oxidation and Functional Recovery After Low-Flow Ischemia and Reperfusion in the Isolated Perfused Rat Heart

“…32 Thus, it is possible that the insulin effects are mediated primarily at the time of reperfusion. For example, Jonassen et al 33 reported that increased levels of insulin administered at the time of reperfusion afforded significant protection that was mediated independently of effects of glucose metabolism and was associated with activation of cell survival signaling pathways.…”