title: Heat production during contraction in skeletal muscle of hypothyroid mice.
abstract: The effect of hypothyroidism on tension-independent and -dependent heat produced during a twitch and a tetanic contraction of extensor digitorum longus (EDL) and soleus muscle of mice was examined. The amount of heat produced during a twitch and the rate of heat development during a tetanus of EDL and soleus were measured at and above optimal length. The effect of hypothyroidism on force production was less than 30%. Straight lines were used to fit the relation between heat production and force. Hypothyroidism significantly decreases tension-independent heat during contraction of EDL and soleus muscle. Because the tension-independent heat is considered to be related to the Ca2+ cycling, these findings suggest that ATP splitting due to the Ca2+ cycling is reduced in hypothyroid mice. This conclusion was strengthened by the observation that the oxalate-supported Ca2+-uptake activity and Ca2+-loading capacity of muscle homogenates from hypothyroid mice were reduced, respectively, to 51 and to 65% in soleus and to 63 and 73% in EDL muscle as compared with euthyroid mice. The tension-dependent rate of heat development during a tetanus was also decreased in soleus muscle of hypothyroid mice. This suggests a lower rate of ATP hydrolysis related to cross-bridge cycling in this muscle due to the hypothyroid state.
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D001833:Body Temperature Regulation; D002118:Calcium / Q000378:metabolism; D007037:Hypothyroidism / Q000378:metabolism / Q000503:physiopathology*; D008297:Male; D051379:Mice; D008815:Mice, Inbred Strains; D009119:Muscle Contraction; D009132:Muscles / Q000378:metabolism
chemical_list: D002118:Calcium