Glycolysis vs. respiration as ATP source for the shape of quiescent cardiomyocytes

ATP concentration ([ATP]) and the fraction of rod-shaped myocytes (Rrod) were measured for quiescent ventricular cells isolated from the rat heart. The myocytes were gently shaken with metabolic inhibitors for 30 min at 37 degrees C, and then [ATP] was assayed enzymatically. [ATP] (mean +/- SE in nmol.(10(6) cells)-1) of the control group (80.2 +/- 6.3) was significantly reduced to 32.3 +/- 3.6 and 21.9 +/- 4.5 by inhibiting glycolysis with 2-deoxyglucose (DG, 10 mM) and iodoacetic acid (IAA, 2 mM), respectively. Inhibition of the oxidative phosphorylation by sodium cyanide (CN, 2 mM) or 2,4-dinitrophenol (DNP, 40 microM) did not induce significant [ATP] reduction (56.5 +/- 5.6 or 53.2 +/- 7.5). Rrod were 54.4 +/- 1.9, 47.3 +/- 5.1, 43.3 +/- 3.3, 28.5 +/- 3.6 and 11.6 +/- 1.8% for the control, CN, DNP, DG and IAA groups, respectively. Under glycolytic inhibition with DG, addition of pyruvate (5 mM) with a pyruvate dehydrogenase activator (dichloroacetate (DCA, 1 mM) or (-)isoproterenol (ISO, 10 microM)) restored [ATP] to 52.5 +/- 8.3 and 67.7 +/- 7.2, respectively, but Rrod still remained depressed (34.6 +/- 2.1 and 35.4 +/- 1.3%). We conclude that the normal shape of quiescent myocytes is maintained primarily by glycolytic ATP.