title: The effects of repeated exposure to anoxia on intracellular calcium, glycogen and lactate in isolated ferret heart muscle.
abstract: Isolated cardiac tissue from the ferret was repeatedly exposed to anoxia while perfused with glucose-containing Tyrode solution. In one series of experiments, papillary muscles were injected with aequorin to measure intracellular Ca2+. On the first exposure to anoxia, the Ca2+ transients often increased, but on subsequent exposures this increase disappeared and eventually the Ca2+ transients declined on exposure to anoxia. This decline in the Ca2+ transients could be converted back to an increase by a 1 h exposure to an elevated (x5) glucose concentration. Exposure of aerobic muscles to 10 mM lactic acid caused a similar increase in the Ca2+ transients to that seen in early exposures to anoxia. In a second series of experiments, performed on Langendorff-perfused hearts, measurements were made of glycogen concentration preceding, and lactate production during, exposures to anoxia. At a constant level of glucose, glycogen concentration and lactate production were found to decline on repeated exposures to anoxia, and both were increased after a period of elevated glucose and reduced stimulation frequency. These results suggest that the response of the Ca2+ transients to anoxia is dependent on the metabolic status of the muscle. The increase in the Ca2+ transients during an early exposure to anoxia may be a consequence of lactic acid production due to accelerated glycolysis. Repeated exposures to anoxia reduce glycogen concentration and lactate production and this reduces the rise in the Ca2+ transients.
authors.affiliation: Department of Physiology, University College London, Great Britain.
authors.forename: J A
authors.initials: JA
authors.lastname: Lee
authors.forename: D G
authors.initials: DG
authors.lastname: Allen
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D005289:Ferrets; D006003:Glycogen / Q000378:metabolism*; D000860:Hypoxia / Q000378:metabolism*; D066298:In Vitro Techniques; D007773:Lactates / Q000378:metabolism*; D009206:Myocardium / Q000378:metabolism*; D010210:Papillary Muscles / Q000378:metabolism*
chemical_list: D007773:Lactates; D006003:Glycogen; D002118:Calcium