Effects of thyroid hormones on the biochemical specialization of human muscle fibers.
The effects of thyrotoxicosis and of hypothyroidism on human muscle have been studied on single fiber preparations. In thyrotoxic muscle, the ratio between fibers showing the fast type of myofibrillar protein isoforms (fast fibers) and fibers showing the slow type (slow fibers) is increased, as is the percentage of fibers with incomplete segregation of fast and slow myosin (intermediate fibers). Furthermore, in fast fibers, the volume and, to a greater extent, the rate of Ca transport of sarcoplasmic reticulum (SR) are increased, without changes in the affinity for Ca2+ of the Ca-pump or in its sensitivity to the cyclic adenosine monophosphate (cAMP) dependent protein kinase system. These effects are completely reversed by the removal of thyroid hormones, as demonstrated by hypothyroid muscles. It is suggested that in human muscle cells thyroid hormones are critical for the expression of fast genes and for SR Ca transport.
Salviati
G
G
Centro di Studio per la Biologia e Fisiopatologia Muscolare del Consiglio Nazionale delle Ricerche, Istituto di Patologia Generale, University of Padova, Italy.
Zeviani
M
M
Betto
R
R
Nacamulli
D
D
Busnardo
B
B
D000328:Adult; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004591:Electrophoresis, Polyacrylamide Gel / Q000379:methods; D005260:Female; D006801:Humans; D006980:Hyperthyroidism / Q000473:pathology; D007037:Hypothyroidism / Q000473:pathology; D008875:Middle Aged; D018485:Muscle Fibers, Skeletal / Q000145:classification / Q000187:drug effects* / Q000378:metabolism; D009218:Myosins / Q000378:metabolism; D012519:Sarcoplasmic Reticulum / Q000187:drug effects; D013959:Thyroid Diseases / Q000473:pathology*; D013963:Thyroid Hormones / Q000494:pharmacology*
D013963:Thyroid Hormones; D000242:Cyclic AMP; D009218:Myosins; D002118:Calcium