Anoxic cardiac performance in Amazonian and north-temperate-zone teleosts

Amazonian fish face periodic conditions of hypoxic water not commonly encou ntered by most other species. We examined the impact of simulated anoxia on cardiac performance of Amazonian species relative to north-temperate-zone species to assess whether the ability to maintain anoxic heart performance is related to either respiratory strategy or geographic location. Four Amaz onian species (acara-acu (Astronotus ocellatus), acari-bodo (Lipossarcus pa rdalis), tambaqui (Colossoma macropomum), and tamoata (Hoplosternum littora le)) and four north-temperate-zone species (American eel (Anguilla rostrata ), bullhead (Ictalurus punctatus). yellow perch (Perca flavescens), and rai nbow trout (Oncorhynchus mykiss)) were studied. The Amazonian species displ ay a range of respiratory modes from obligate,gill-breather to facultative air-breather. The performance of isolated ventricular strips under conditio ns of impaired oxidative phosphorylation was monitored under the same condi tions of temperature (25 degrees C) and contraction frequency (30 bpm) for all species. In all cases, ventricular strips showed a decrease in the forc e of contraction with sodium cyanide (NaCN) treatment. Ventricular strips f rom two Amazonian and one north temperate-zone species showed signs of reco very from NaCN treatment. There was considerable diversity in the ability o f ventricular strips to develop force under conditions of impaired oxidativ e phosphorylation that was not related to the ability to obtain oxygen from the air or to geographic location. However, there was a major difference b etween Amazonian and north temperate-zone species in the ability of ventric ular strips to maintain resting tension under NaCN treatment. Resting tensi on increased under conditions of simulated anoxia in ventricular strips fro m all north-temperate-zone species, but there was no change in resting tens ion in ventricular strips from Amazonian species. We propose that hearts fr om the Amazonian species are better able to reduce cytoplasmic calcium leve ls, possibly through a more highly developed sarcoplasmic reticulum.