Time course of changes in in vitro sarcoplasmic reticulum Ca2+-handling and Na+-K+-ATPase activity during repetitive contractions

Abstract

Time-dependent changes in sarcoplasmic reticulum (SR) Ca2+-handling and Na+-K+-ATPase activity, as assessed in vitro, were investigated in the superficial (GS) and deep regions (GD) of rat gastrocnemius muscles undergoing short-term (up to 30 min) electrical stimulation. There was a rapid and progressive loss of force output during the first 5 min of stimulation. For GS, significant depressions (P < 0.05) in SR Ca2+-uptake rate and Ca2+-ATPase activity were observed during only the first 1 min. No further reductions occurred with stimulation time. SR Ca2+-release rate was significantly (P < 0.05) decreased at 3 min. For GD, significant reductions (P < 0.05) in Ca2+-uptake rate, Ca2+-release rate and Ca2+-ATPase activity were manifested after 3, 5, and 5 min, respectively. A decay in Na+-K+-ATPase activity was found only in 1-min stimulated GD and 30-min stimulated GS. After 30 min, the depressed functions reverted to resting levels in GD but not in GS. The alterations in any variables examined were not parallel with changes in force output. These results suggest that, at least under the conditions used in this study, in vivo disruptions in cation regulation mediated by vigorous contractile activity would be attributable primarily to events other than structural alterations to the respective proteins.

Na+-K+-ATPase in rat skeletal muscle: muscle fiber-specific differences in exercise-induced changes in ion affinity and maximal activity

“…Two studies have reported a decrease in maximal pump capacity after muscle activity (8,20), two studies reported an unchanged maximal capacity (10,16), whereas one study reported a substantial increase in activity (26). These results were all obtained using the 3-O-methylfluorescein phosphate (3-O-MFP) assay, which employs 3-O-MFP as an artificial substrate, without involving ATP hydrolysis (23).…”

“…Maximal Na ϩ -K ϩ -ATPase in vitro activity in rat muscle measured using the 3-O-MFPase assay has been reported to be reduced, unchanged, or increased after muscle activity. In situ stimulation and treadmill running both reduce maximal 3-O-MFPase activity in rats (8,20). In addition, treadmill running and in vitro electrical stimulation reportedly have no impact on maximal 3-O-MFPase activity (10,16), and in situ electrical stimulation has been reported to substantially increase maximal 3-OMFPase activity (26).…”

Enhanced activity of eccentric contraction induces alterations in <i>in vitro</i> sarcoplasmic reticulum Ca²⁺ handling in rat hindlimb muscles

“…The third result in this study was a significant ECCdependent decline in Na + -K + -ATP pump function beyond 100 repetitions compared with the control muscle, which is consistent with a previous study that evaluated 200 ECC repetitions 35) . In addition, approximately 50% of all the Na + -K + pumps, which play a role in maintaining Na + and K + gradients across the sarcolemma and t-tubules, are located in the intracellular junctions between the SR and t-tubule invaginations of the plasma membrane 36) .…”

The Efficacy of Microcurrent Therapy on Eccentric Contraction-Induced Muscle Damage in Rat Fast-Twitch Skeletal Muscle

“…SR Ca 2+ -uptake and release rates were measured using the Ca 2+ fluorescent dye indo-1 as previously described [19]. Briefly, aliquots of the homogenate were incubated for 3 min at 37˚C in the assay buffer (pH 7.0) composed of 100 mM KCl, 20 ] was monitored using a fluorometer (CAF-110, Nihon-Bunko, Japan) and was computed according to the ratiometric method [20].…”