title: Gender- and age-related differences in the regulatory influence of thyroid hormone on the contractility and myosin composition of single rat soleus muscle fibres.
abstract: The effects of 4 weeks of thyroid hormone (3,5,3'-triiodothyronine, T3) treatment on the myosin isoform composition and maximum velocity of unloaded shortening (V0) of single soleus muscle fibres of young (3-6 months) and old (20-24 months) female (149 fibres) and male (200 fibres) rats were studied. Gender-related differences in the up-regulation of fast myosin heavy chain (MyHC) and myosin light chain (MyLC) isoforms were observed. In the female hyperthyroid rats, pure type I fibres and fibres co-expressing type I and type IIA MyHC (type I/IIA fibres) predominated. Some fibres expressed an alpha cardiac-like MyHC isoform either purely (alpha cardiac-like fibre type) or in co-expression with IIA MyHC (alpha cardiac-like/IIA fibre type). In the male hyperthyroid rats, on the other hand, all fibres were either type I/IIA or type I/IIAX. The relative quantities of fast MyLC isoforms in type I/IIA and type I/IIAX fibres was higher in female than in male hyperthyroid rats. V0 was similar in male and female control rats, and decreased with age in both genders (P<0.001). After T3 treatment, the average V0 increased (P<0.001) in females with a concomitant up-regulation of fast MyHC and fast MyLC isoforms irrespective of age. The average V0 of the pooled fibres was higher (P<0.001) in female than in male hyperthyroid rats at both ages. In conclusion, gender- and age-related differences were observed in the regulatory influence of 4 weeks' T3 treatment on myosin isoform composition and V0 in soleus fibres. These differences are presumably related to an interaction of thyroid and sex hormones in the regulation of myosin gene expression.
authors.affiliation: Noll Physiological Research Center, Pennsylvania State University, 119 Noll Laboratory, University Park, PA 16802-6900, USA.
authors.forename: F
authors.initials: F
authors.lastname: Yu
authors.forename: H
authors.initials: H
authors.lastname: Degens
authors.forename: X
authors.initials: X
authors.lastname: Li
authors.forename: L
authors.initials: L
authors.lastname: Larsson
mesh_terms: D000375:Aging; D000818:Animals; D005260:Female; D006801:Humans; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects*; D018482:Muscle, Skeletal / Q000737:chemistry / Q000187:drug effects* / Q000502:physiology; D018995:Myosin Heavy Chains / Q000032:analysis; D018994:Myosin Light Chains / Q000032:analysis; D009218:Myosins / Q000032:analysis*; D051381:Rats; D017208:Rats, Wistar; D012727:Sex Characteristics; D013963:Thyroid Hormones / Q000494:pharmacology*; D014284:Triiodothyronine / Q000494:pharmacology
chemical_list: D018994:Myosin Light Chains; D013963:Thyroid Hormones; D014284:Triiodothyronine; D018995:Myosin Heavy Chains; D009218:Myosins