Effects of sprint training on contractility and [Ca ]i transients in adult rat myocytes

Zhang, Xue-Qian, Jianliang Song, Lois L. Carl, Weixing Shi, Anwer Qureshi, Qiang Tian, and Joseph Y. Cheung. Effects of sprint training on contractility and [Ca2 ]i transients in adult rat myocytes. J Appl Physiol 93: 1310–1317, 2002. First published July 5, 2002; 10.1152/ japplphysiol.01071.2001.—The effects of 6–8 wk of highintensity sprint training (HIST) on rat myocyte contractility and intracellular Ca2 concentration ([Ca2 ]i) transients were investigated. Compared with sedentary (Sed) myocytes, HIST induced a modest (5%) but significant (P 0.0005) increase in cell length with no changes in cell width. In addition, the percentage of myosin heavy chain -isoenzyme increased significantly (P 0.02) from 0.566 0.077% in Sed rats to 0.871 0.006% in HIST rats. At all three (0.6, 1.8, and 5 mM) extracellular Ca2 concentrations ([Ca2 ]o) examined, maximal shortening amplitudes and maximal shortening velocities were significantly (P 0.0001) lower and half-times of relaxation were significantly (P 0.005) longer in HIST myocytes. HIST myocytes had significantly (P 0.0001) higher diastolic [Ca2 ]i levels. Compared with Sed myocytes, systolic [Ca2 ]i levels in HIST myocytes were higher at 0.6 mM [Ca2 ]o, similar at 1.8 mM [Ca2 ]o, and lower at 5 mM [Ca2 ]o. The amplitudes of [Ca2 ]i transients were significantly (P 0.0001) lower in HIST myocytes. Half-times of [Ca2 ]i transient decline, an estimate of sarcoplasmic reticulum (SR) Ca2 uptake activity, were not different between Sed and HIST myocytes. Compared with Sed hearts, Western blots demonstrated a significant (P 0.03) threefold decrease in Na /Ca2 exchanger, but SR Ca2 -ATPase and calsequestrin protein levels were unchanged in HIST hearts. We conclude that HIST effected diminished myocyte contractile function and [Ca2 ]i transient amplitudes under the conditions studied. We speculate that downregulation of Na /Ca2 exchanger may partly account for the decreased contractility in HIST myocytes.