Metabolic suppression in anoxic frog muscle.

Microcalorimetry is the only direct method for measuring moment-to-moment changes in whole-cell metabolism (as heat output) during anoxia. We have adapted this methodology, in conjunction with standard muscle isolation techniques, to monitor metabolic transitions in isolated frog (Rana temporaria) sartorius muscle during anoxia and recovery (reoxygenation). Anoxia (sustained 1 h, following 2 h progressive hypoxia) suppressed muscle heat output to 20% of the stable normoxic level. This effect was fully reversible upon reoxygenation. Metabolite profiles were consistent with other anoxia-tolerant vertebrates--most notably, adenosine triphosphate (ATP) content during anoxia and reoxygenation remained unchanged from normoxia (pre-anoxic control). In addition, the concentration of K+ ions ([K+]) in interstitial dialysates remained stable (2-3 mM) throughout anoxia and recovery. Interstitial [lactate-] increased slightly, in accord with anaerobiosis supporting suppressed metabolic rates during anoxia. The degree of anoxic suppression of metabolism observed is similar to other vertebrate models of anoxia tolerance. Furthermore, stable ATP concentrations and interstitial [K+] in the isolated tissue suggests that intrinsic mechanisms suppress metabolism in a manner that coordinates ATP supply and demand and avoids the severe ion imbalances that are characteristics of hypoxia-sensitive systems.