GLYCOLYTIC INHIBITION - EFFECTS ON DIASTOLIC RELAXATION AND INTRACELLULAR CALCIUM HANDLING IN HYPERTROPHIED RAT VENTRICULAR MYOCYTES

We tested the hypothesis that glycolytic inhibition by 2-deoxyglucose causes greater impairment of diastolic relaxation and intracellular calcium handling in well-oxygenated hypertrophied adult rat myocytes compared with control myocytes. We simultaneously measured cell motion and intracellular free calcium concentration ([Ca2+](i)) with indo-1 in isolated paced myocytes from aortic-banded rats and sham-operated rats. There was no difference in either the end-diastolic or peak-systolic [Ca2+](i) between control and hypertrophied myocytes (97+/-18 vs. 105+/-15 nM, 467+/-92, vs. 556+/-67 nM, respectively). Myocytes were first superfused with oxygenated Hepes-buffered solution containing 1.2 mM CaCl2, 5.6 mM glucose, and 5 mM acetate, and paced at 3 Hz at 36 degrees C. Exposure to 20 mM 2-deoxyglucose as substitution of glucose for 15 min caused an upward shift of end-diastolic cell position in both control (n = 5) and hypertrophied myocytes (n = 10) (P < 0.001 vs, baseline), indicating an impaired extent of relaxation, Hypertrophied myocytes, however, showed a greater upward shift in end-diastolic cell position and slowing of relaxation compared with control myocytes (Delta 144+/-28 vs. 55+/-15% of baseline diastolic position, P < 0.02). Exposure to 2-deoxyglucose increased end-diastolic [Ca2+](i) in both groups (P < 0.001 vs. baseline),but there was no difference between hypertrophied and control myocytes (218+/-38 vs. 183+/-29 nM, respectively). The effects of 2-deoxyglucose were corroborated in isolated oxygenated perfused hearts in which glycolytic inhibition which caused severe elevation of isovolumic diastolic pressure and prolongation of relaxation in the hypertrophied hearts compared with controls. In summary, the inhibition of the glycolytic pathway impairs diastolic relaxation to a greater extent in hypertrophied myocytes than in control myocytes even in well-oxygenated conditions. The severe impairment of af diastolic relaxation induced by 2-deoxyglucose in hypertrophied myocytes compared with control myocytes cannot be explained by greater diastolic Ca2+ overload, which implicates an increase in myofilament Ca2+-responsiveness is a possible mechanism.