Calcium activation of sarcoplasmic reticulum ATPase following strenuous activity

Abstract

The purpose of this study was to examine the effects of varying Ca²⁺ concentration on the 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 (β-aminoethyl ether)-N,N′-tetraacetic acid (EGTA) buffering system. At 1.25 μM 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 μmol P_i∙mg⁻¹∙10 min⁻¹) compared with C values (2.41 ± 0.34 μmol P_i∙mg⁻¹∙10 min⁻¹) (p ≤ 0.05). At 5.0 μM, Ca²⁺ activated ATPase activity remained depressed in the E, 5R, and 15R groups compared with C and 30R groups (p ≤ 0.05). At 0.75 μM Ca²⁺, there was no significant difference between groups (p ≥ 0.05). The results suggest that Ca²⁺ activated SR ATPase activity of fatigued FT muscle may contribute to the decreased force production at exhaustion.