Fiber-type-specific alpha B-crystallin distribution and its shifts with T-3 and PTU treatments in rat hindlimb muscles

Changes in alpha B-crystallin content in adult rat soleus and extensor digitorum longus (EDL) were examined after 8 wk of 3,5,3'-triiodothyronine (T-3) and propylthiouracil (PTU) treatments. Cellular distributions of alpha B-crystallin expression related to fiber type, and distribution shifts with these treatments were also examined in detail from the gray level of reactivity to specific anti-alpha B-crystallin antibody. alpha B-crystallin content in both soleus and EDL muscles was significantly decreased after T-3, and that in EDL was significantly increased over twofold after PTU treatment. In both control soleus and EDL muscles, the gray level of type I fibers was higher than that of type II fibers. alpha B-crystallin expression among type II subtypes was muscle specific; the order was type I > IIa > IIx > IIb in control EDL muscle and type IIx greater than or equal to IIa in soleus muscle. The relation was basically unchanged in both muscles after Ts treatment and was, in particular, well maintained in EDL muscle. Under hypothyroidism conditions with PTU, the mean alpha B-crystallin levels of type IIa and IIx fibers were significantly lower than levels under control conditions. Thus the relation between fiber type and the expression manner of stress protein alpha B-crystallin is muscle specific and also is well regulated under thyroid hormone, especially in fast EDL muscle.