[Effect of hypothyroidism on the structural and functional characteristics of the sarcoplasmic reticulum of rabbit skeletal muscles].

Structural and functional characteristics of sarcoplasmic reticulum vesicles (SRV) from skeletal muscle of normal and hypothyroid rabbits were investigated. The rate of Ca2+ absorption was decreased in hypothyroid animals and Ca2-ATPase activity in SRV of these animals was lower than that of control rabbits. The transport ratio (Ca2+/ATP) in hypothyroid rabbits was higher by 20% than in controls. In SRV of hypothyroid animals a decrease in the protein/lipid interaction and higher fluidity of membrane lipids were observed. Administration of L-thyroxine (300 mg/kg of body mass, intraperitoneally) normalized the SR lipids fluidity within about 40 hrs after the injection but did not affect significantly the patterns of protein/lipid interaction. Normal and hypothyroid SRV were similar in their protein spectrum as shown by electrophoresis in polyacrylamide gel. These alterations observed in the SRV structure and function are apparently related to modifications of membrane lipids.