PRESERVATION OF SARCOPLASMIC-RETICULUM CA2+-SEQUESTERING FUNCTION IN HOMOGENATES OF DIFFERENT FIBER-TYPE COMPOSITION FOLLOWING SPRINT ACTIVITY

To examine the effect of exercise on sarcoplasmic reticulum function in muscle tissue of different fibre composition, adult male Wistar rats weighing 388 +/- 23 g (x +/- SE) ran intermittently on a treadmill until fatigue. Fatigue was induced by 15-20 min of running performed at 52 m/min on an 8 degrees incline in periods of 2.5 min of exercise separated by 2 min of recovery. Analysis of sarcoplasmic reticulum Ca2+ ATPase activity determined in homogenates indicated no difference (p > 0.05) between age-matched control and exercised tissue for the soleus (SOL; 0.121 +/- 0.012 vs. 0.156 +/- 0.018 mu mol.mg(-1) protein.min(-1)), red gastrocnemius (RG; 0.381 +/- 0.022 vs. 0.354 +/- 0.022), or white gastrocnemius (WG; 0.526 +/- 0.05 vs. 0.471 +/- 0.031). Similarly, both total ATPase-and Mg2+ ATPase activities were unaffected by the exercise in any of the tissues examined. Exercise also failed to alter sarcoplasmic reticulum Ca2+ uptake in homogenates of the SOL (1.43 +/- 0.15 vs. 1.38 +/- 0.19 nmol.mg(-1) protein.min(-1)), RG (3.74 +/- 0.29 vs. 3.59 +/- 0.24), and WG (5.98 +/- 0.48 vs. 5.41 +/- 0.50). At fatigue, glycogen depletion was similar in all tissue types and amounted to 65.1% in the SOL (172 +/- 9 vs. 60 +/- 16 mmol.glucosyl units(-1).kg(-1) dry weight), 74.4% in RG (164 +/- 8 vs. 42 +/- 6), and 79% in the WG (167 +/- 9 vs. 35 +/- 9). It is concluded that exercise by itself does not alter sarcoplasmic reticulum Ca2+-sequestering function in tissues of primarily different fibre composition when determined in homogenates in vitro. The integrity of sarcoplasmic reticulum function is preserved despite an apparent extensive recruitment of all tissue types during the exercise.