Calcium activation of sarcoplasmic reticulum ATPase following strenuous activity.

The purpose of this study was to examine the effects of varying Ca2+ activated sarcoplasmic reticulum (SR) ATPase activity of fast-twitch (FT) skeletal muscle at exhaustion and during recovery. Wistar rats (200 g) were assigned to control (C), exhausted (E), and three recovery groups (R) at 5, 15, and 30 min. Following exhaustion on a motor-driven treadmill, the gastrocnemius muscles from all groups were excised and frozen. Muscle samples were assayed for ATPase activity in a Ca2+-ethyleneglycol bis (beta-aminoethyl ether)-N,N'-tetraacetic acid (EGTA) buffering system. At 1.25 microM Ca2+, a significant depression in Ca2+ activated ATPase activity occurred in the E, 5R, 15R, and 30R groups (1.61 +/- 0.17, 1.87 +/- 0.14, 1.43 +/- 0.29, and 1.62 +/- 0.1 mumol Pi . mg-1 . 10 min-1) compared with C values (2.41 +/- 0.34 mumol Pi . mg-1 . 10 min-1) (p less than or equal to 0.05). At 5.0 microM, Ca2+ activated ATPase activity remained depressed in the E, 5R, and 15R groups compared with C and 30R groups (p less than or equal to 0.05). At 0.75 microM Ca2+, there was no significant difference between groups (p greater than or equal to 0.05). The results suggest that Ca2+ activated SR ATPase activity of fatigued FT muscle may contribute to the decreased force production at exhaustion.