Thyroxine Induced Transformation in Sarcoplasmic Reticulum of Rabbit Soleus and Psoas Muscles

Abstract

The properties of the sarcoplasmic reticulum membranes isolated from slow-twitch type I soleus and fast-twitch type II psoas muscles of control and thyroxine treated rabbits were comparatively studied. Membrane yield, maximal calcium storing capacity, ATP-supported calcium uptake, calcium-dependent ATPase activity and calcium-dependent phosphoprotein formation were found to be 3-10 fold higher in psoas than in soleus preparations. Membrane yield, calcium-dependent ATPase activity, ATP-supported calcium transport and calcium-dependent phospho­ protein are at least twice enhanced in the membranes from soleus muscles of animals treated for 14-21 days with thyroxine. The corresponding capacities of the membranes from psoas muscles are not further augmented by the same thyroxine treatment. The maximal calcium storing capaci­ ty of the psoas membranes is their sole specific property which is significantly increased. The changes in the properties of the soleus muscles’ sarcoplasmic reticulum membranes are engen­dered by an increase from 5 to 30-50% in the number of type II fibres. Since the calcium transporting properties of the sarcoplasmic reticulum membranes from type II fibres qualitatively differ from those of type I fibres, thyroxine does not only affect quantitative but also qualitative parameters of the muscles’ sarcoplasmic reticulum membrane system.

American Thyroid Association Guide to Investigating Thyroid Hormone Economy and Action in Rodent and Cell Models

“…Antibodies discriminating between these isoforms have been described (708) and although some caution is warranted when using currently available commercial antibodies (709), multicolor immunofluorescence analysis has been described for the simultaneous assessment of expression of all MHC isoforms in rat and mouse skeletal muscle using these antibodies (710). More typically, a histochemical method for myofibrillar ATPase expression is widely used which distinguishes between Type I fibers (MHC I), Type IIB fibers (MHC IIb), and intermediate fibers (MHC IIa, MHC IIx/d) (684,692,700,702,711). Muscles are clamped at their approximate in situ length and frozen in liquid N 2 -cooled freon or isopentane.…”

Effect of triiodothyronine on the maxilla and masseter muscles of the rat stomatognathic system

“…Even though the methodology employed to classify the fibers has certain limitations (32), the results obtained by T3 treatment were somehow expected, since T3 is known to increase type II fibers in skeletal muscle (33). However, thyroidectomy was shown to reduce Mb content and T3 treatment was unable to restore it to control levels.…”

Hormônios tireóideos, UCPs e termogênese

“…O ciclo do cálcio (entre o citosol e o retículo sarcoplasmático), responsável pela contração e relaxamento muscular, consome grande quantidade de energia. Também aqui, os hormônios tireóideos têm papel fundamental, regulando a expressão dos genes que codificam as diferentes isoformas da cadeia pesada da miosina (MHC) (19) e do transportador de cálcio (SERCA) (20,21). O T3 estimula a expressão da isoforma de MHC com maior atividade catalítica e, portanto, maior atividade ATPásica.…”