EFFECTS OF SPACE-FLIGHT ON GLUT-4 CONTENT IN RAT PLANTARIS MUSCLE

The effects of 14 days of space flight on the glucose transporter prot ein (GLUT-4) were studied in the plantaris muscle of growing 9-week-ol d, male Sprague Dawley rats. The rats were randomly separated into fiv e groups: pre-flight vivarium ground controls (PF-VC) sacrificed appro ximately 2 h after launch; flight groups sacrificed either approximate ly 5 h (F-R0) or 9 days (F-R9) after the return from space; and synchr onous ground controls (SC-R0 and SC-R9) sacrificed at the same time as the respective flight groups. The flight groups F-R0 and F-R9 were ex posed to micro-gravity for 14 days in the Spacelab module located in t he cargo bay of the shuttle transport system -58 of the manned Space S huttle for the NASA mission named ''Spacelab Life Sciences 2''. Body w eight and plantaris weight of SC-R0 and F-R0 were significantly higher than those of PF-VC. Neither body weight nor plantaris muscle weight in either group had changed 9 days after the return from space. As a r e suit, body weight and plantaris muscle weight did not differ between the flight and synchronous control groups at any of the time points i nvestigated. The GLUT-4 content (cpm/mu g membrane protein) in the pla ntaris muscle did not show any significant change in response to 14 da ys of space flight or 9 days after return. Similarly, citrate synthase activity did not change during the course of the space flight or the recovery period. These results suggest that 14 days of space flight do es not affect muscle de mass or GLUT-4 content of the fast-twitch plan taris muscle in the rat.