STRUCTURAL AND BIOCHEMICAL ANALYSES OF CARDIAC VENTRICULAR ENLARGEMENT IN COLD-ACCLIMATED STRIPED BASS

Structural and biochemical analyses of cardiac ventricular enlargement in cold-acclimated striped bass. Am. J. Physiol. 273 (Regulatory Inte grative Comp. Physiol. 42): R252-R258, 1997.-We examined effects of te mperature acclimation on ultrastructural characteristics of cardiac my ocytes and maximal activities of metabolic enzymes in cardiac tissue o f striped bass (Morone saxatilis). Ventricular mass and ventricular ma ss divided by body weight were significantly increased (29% and 40%, r espectively) in animals acclimated to cold (5 degrees C) vs. warm temp eratures (25 degrees C). Mean myocyte diameter was increased at cold t emperature (3.47 +/- 0.14 vs. 2.95 +/- 0.08 pm), which is sufficient t o explain the increase in ventricular mass. Ventricular enlargement di d not alter volume densities of mitochondria, myofibrils, protein conc entration, or citrate synthase activity. Thus total volume of mitochon dria and myofibrils increased proportionately with cardiac mass in col d animals. Activities of hexokinase (34%) and carnitine palmitoyltrans ferase (42%) increased in cold animals, suggesting positive compensati on and increased aerobic capacity for utilization of glucose and fatty acids for energy production. Enlargement of the ventricle and an incr eased capacity for ATP production in striped bass may help compensate for kinetic constraints at cold temperatures and maintain circulatory support to oxidative axial musculature for swimming activity.