Fatigue-induced change in T-system excitability and its major cause in rat fast-twitch skeletal muscle in vivo.

In conclusion, T-system excitability is decreased after high-intensity exercise due at least in part to the S-glutathionylation of Na+-K+ ATPase, which may be enhanced by contraction-induced ATP depression. ABSTRACT: The purpose of this study was to investigate a transverse tubular system (T-system) excitability after skeletal muscle contractions in vivo, and the contribution of S-glutathionylation of Na+ -K+ ATPase. T-system excitability was estimated by measuring repriming period (RP) required for double action potentials in mechanically-skinned fibres where the sarcolemma was removed but T-system still works. The RP under partially depolarized condition is highly dependent on the function of Na+ -K+ ATPase. Rat gastrocnemius (GAS) muscles were subjected to repetitive contractions until force was decreased to ∼50% of initial force, and then the muscles were very quickly excised and used for skinned fibre and biochemical experiments. The RP under partially depolarized condition was increased in stimulated fibres (5.9 ± 1.0 ms in rested vs. 8.0 ± 1.5 ms in stimulated), however this increased RP was reversed by sequential treatment with dithiothreitol. The skinned fibres from rested muscles exhibited slower repriming only when treated with oxidized glutathione (GSSG) under very low ATP (≤1 mM) conditions, whereas the RP in stimulated fibres was not altered after GSSG treatment without ATP. In line with this, the α2 and β subunit of Na+ -K+ ATPase were mor...
Source: The Journal of Physiology - Category: Physiology Authors: Tags: J Physiol Source Type: research