Shortening and [Ca2+] dynamics of left ventricular myocytes isolated from exercise-trained rats

Department of Kinesiology and Applied Physiology University of Colorado at Boulder, Boulder, Colorado 80309 The effects of run endurance training and fura 2 loading on the contractile function and Ca 2+ regulation of rat left ventricular myocytes were examined. In myocytes not loaded with fura 2, the maximal extent of myocyte shortening was reduced with training under our pacing conditions [0.5 Hz at 2.0 and 0.75 mM external Ca 2+ concentration ([Ca 2+ ] o )], although training had no effect on the temporal characteristics. The "light" loading of myocytes with fura 2 markedly suppressed (~50%) maximal shortening in the sedentary and trained groups, although the temporal characteristics of myocyte shortening were significantly prolonged in the trained group. No discernible differences in the dynamic characteristics of the intracellular Ca 2+ concentration ([Ca 2+ ]) transient were detected at 2.0 mM [Ca 2+ ] o , although peak [Ca 2+ ] and rate of [Ca 2+ ] rise during caffeine contracture were greater in the trained state at 0.75 mM [Ca 2+ ] o . We conclude that training induced a diminished myocyte contractile function under the conditions studied here and a more effective coupling of inward Ca 2+ current to sarcoplasmic reticulum Ca 2+ release at low [Ca 2+ ] o , and that fura 2 and its loading vehicle DMSO significantly alter the intrinsic characteristics of myocyte contractile function and Ca 2+ regulation. fura 2; dimethyl sulfoxide; caffeine contracture; edge detection