1.EFFECTS OF ECCENTRIC CONTRACTIONS ON IN VITRO Na+-K+-ATPase ACTIVITY AND SARCOPLASMIC RETICULUM Ca2+-SEQUESTERING IN RAT SKELETAL MUSCLE
KEITA KANZAKI ; MAI KURATANI ; SATOSHI MATSUNAGA ; TAKAAKI MISHIMA ; SACHIO USUI ; MASANOBU WADA
Japanese Journal of Physical Fitness and Sports Medicine 2010;59(4):337-348
The purpose of this study was to examine the effects of eccentric contractions (Ecc) on cation (i.e., K+, Na+ and Ca2+) regulation in skeletal muscle. The left anterior crural muscles of male Wistar rats were subjected in vivo to either Ecc or isometric contrations (Iso) for 200 cycles. The extensor digitorum longus and tibialis anterior muscles were removed immediately after and 2, 4 and 6 days following contractions and used for measures of force output and biochemical analyses, respectively. Ecc led to a 75% decrease in maximal tetanic force. Decreased force output did not revert to pre-exercise levels during 6 days of recovery. Sarcoplasmic reticulum (SR) Ca2+-ATPase activity was reduced by 52 and 60% 4 and 6 days after Ecc, respectively. The reduction in catalytic activity after 6 days was accompanied by a 63% decrease in SR Ca2+-ATPase protein and an approximately 3.5-fold increase in calpain activity. Na+-K+-ATPase acticity was decreased by 23% immediately after Ecc and restored during 2 days of recovery. These alterations were specific for Ecc and not observed for Iso. These results suggest that disturbances in cation regulation may account, at least partly, for Ecc-induced decreases in force and power which can take a number of days to recover and that the decrease in SR Ca2+-ATPase activity would result from the degradation of the enzyme.
2.Effects of single ingestion of arginine on mTORC1 activation in rat fast- and slow-twitch muscles
Keita KANZAKI ; Yuki YAMASAKI ; Masanobu WADA
Japanese Journal of Physical Fitness and Sports Medicine 2022;71(2):213-225
This study aimed to examine whether a single ingestion of arginine activates the mammalian target of rapamycin complex 1 (mTORC1) in rat fast- and slow-twitch skeletal muscles. In the first experiment, the rats were orally administered arginine (3 or 10 mmol/kg body weight) in water. The plantaris, gastrocnemius, and soleus muscles were excised 1 h after the administration. Immunoblot analysis showed that the administration with a higher dose (10 mmol/kg) resulted in increased phosphorylation of ribosomal S6 kinase (S6K) and ribosomal protein S6 only in the soleus muscles. The amounts of cellular arginine sensor for mTORC1 subunit 1 (CASTOR1) expressed were similar in these three muscles. In the second experiment, the plantaris and soleus muscles were excised 1 h after the administration of 10 mmol/kg of arginine. The binding of CASTOR1 to the GATOR2 complex was not detected in either muscle in co-immunoprecipitation and immunoblot analyses, irrespective of arginine administration. In the third experiment, a role of nitric oxide (NO) was elucidated. Treatment with an inhibitor of NO synthase blocked the arginine-induced increase in S6K phosphorylation. These results indicate that a single ingestion of arginine is capable of activating mTORC1 only in slow-twitch muscles and suggest that the activation may be mediated via NO, but not via the CASTOR1-GATOR2 complex pathway.