Muscle sarcoplasmic reticulum calcium regulation in humans during consecutive days of exercise and recovery

Abstract

The study investigated the hypothesis that three consecutive days of prolonged cycle exercise would result in a sustained reduction in the Ca2+-cycling properties of the vastus lateralis in the absence of changes in the sarcoplasmic (endoplasmic) reticulum Ca2+-ATPase (SERCA) protein. Tissue samples were obtained at preexercise (Pre) and postexercise (Post) on day 1 (E1) and day 3 (E3) and during recovery day 1 (R1), day 2 (R2), and day 3 (R3) in 12 active but untrained volunteers (age 19.2 ± 0.27 yr; mean ± SE) and analyzed for changes (nmol·mg protein−1·min−1) in maximal Ca2+-ATPase activity ( Vmax), Ca2+uptake and Ca2+release (phase 1 and phase 2), and SERCA isoform expression (SERCA1a and SERCA2a). At E1, reductions ( P < 0.05) from Pre to Post in Vmax(150 ± 7 vs. 121 ± 7), Ca2+uptake (7.79 ± 0.28 vs. 5.71 ± 0.33), and both phases of Ca2+release (phase 1, 20.3 ± 1.3 vs. 15.2 ± 1.1; phase 2, 7.70 ± 0.60 vs. 4.99 ± 0.48) were found. In contrast to Vmax, which recovered at Pre E3 and then remained stable at Post E3 and throughout recovery, Ca2+uptake remained depressed ( P < 0.05) at E3 Pre and Post and at R1 as did phase 2 of Ca2+release. Exercise resulted in an increase ( P < 0.05) in SERCA1a (14% at R2) but not SERCA2a. It is concluded that rapidly adapting mechanisms protect Vmaxfollowing the onset of regular exercise but not Ca2+uptake and Ca2+release.