Control of glycolysis in ischemic and anoxic rat heart

37 CONTROL OF GLYCOLYSIS IN ISCHEMIC AND ANOXIC RAT HEART. Mochizuki,S. and Neely,J.R. *Dep.Med. Jikei Univ.Sch.Med. Tokyo,Japan & Dep.Physiol. Penn.St.lJniv. 17033,U.S.A.* Cardiac muscle derives its energy from oxidative metabolism and can produce less than 10% of its normal ATP requirements anaerobically. Of maximally stimulated, ATP production by glycolysis could partially compensate for the loss of ener y when oxidative pathways are limited and might reduce ccl 7 damage. The purpose of the present study was to determine the regulatory mechanism in glycolysis of the ischemic rat myocardium. Hearts were perfused with Krebs bicarbonate buffer containing 1lmM lucose by either the Langendorff preparation for anoxia(95, $ N2, 5% C02) or the working heart preparation for ischemia(95% 02, 5% C02). Ischemia was induced by use of a one-way valve in the aortic outflow tract. Rates of glycolysis were estimated by measuring the rate of 3H20 production from (2-3H) glucose. Glyceraldehyde-3phosphate dehydrogenase(GAPdh) was isolated form rat hearts and the activity of GAPdh was assayed spectrophotometrically. The rate of.glycolysis in hearts with.oxygenated perfu~7:; variedmwith the degree of restriction in coronary . A 60/. reduction in coronary flow resulted in an accelerated rate of glycolysis but at lower flows glycolysis became inhibited. Restriction of glycolysis in the ischemic hearts appeared to develop at the level of GAPdh and was related to several than es in the intracellar environment. Tissue lactate, H$ and NADH all accumulated. Addition of L-lactate(20mM) or H+(pH 6.8-7.0) to the perfusate inhibited glycolysis in aerobic and anoxic hearts. Also, glycolysis was reduced in mildly ischemic hearts by addition of L-lactate(20mM) or pyruvate(lOmM) to the buffer. L-lactate in the perfusate appeared to inhibit glycolysis at the level of GAPdh and was related to a high c;rtosolic NADH, whereas pyruvate inhibited phosphofructokinase(PFK) due to high tissue levels of citrate. The activity of GAPdh isolated from normal cardiac muscle and assayed in vitro was markedly reduced by either lowering pH from 7.0 to 6.5 or addition of NADH to the buffer. The NADH inhibition was only partially relieved by inorganic phosphate(Pi). ATP was also a strong inhibitor and its inhibition could be completely relieved b Pi. Lactate at 20mM inhibited the activity of GAPdh by a 4;out 50% at cellular concentration of glyceraldehyde-3-phosphate. Glycolysis is accelerated by anoxia when coronary flow is maintained. However, anoxia failed to increase glycolysis when the anoxic perfusion was started after the hearts had been ischemic for either 5 or 30 min. This suggest that the ischemic inhibition of glycolysis is not easily reversed. In summary, glycolytic inhibition in ischemic hearts most likely results from a combined effect of high concentrations of H+, NADH and lactate and this inhibition could *Ot be relieved by anoxic perfusion,