Decreased rates of Ca(2+)-dependent heat production in slow- and fast-twitch muscles from the dystrophic (mdx) mouse.

Using a newly developed microcalorimetric approach to assess the rate of energy expenditure for intracellular [Ca2+] homeostasis in isolated muscles at rest, we found this was lower in mdx than in control mouse muscles, by 62% and 29% in soleus and extensor digitorum longus, respectively. Differences in total and Ca(2+)-dependent rates of specific heat production between mdx and control were enhanced during sustained, KCl-induced stimulation of energy dissipation. These results suggest that the low sarcoplasmic energy status of dystrophic muscles is not due to any excessive energy expenditure for intracellular [Ca2+] homeostasis.