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

Amazonian fish face periodic conditions of hypoxic water not commonly encountered 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 Amazonian species (acara-acu (Astronotus ocellatus), acari-bodo (Lipossarcus pardalis), tambaqui (Colossoma macropomum), and tamoata (Hoplosternum littorale)) and four north-temperate-zone species (American eel (Anguilla rostrata), bullhead (Ictalurus punctatus). yellow perch (Perca flavescens), and rainbow trout (Oncorhynchus mykiss)) were studied. The Amazonian species display a range of respiratory modes from obligate,gill-breather to facultative air-breather. The performance of isolated ventricular strips under conditions of impaired oxidative phosphorylation was monitored under the same conditions of temperature (25 degrees C) and contraction frequency (30 bpm) for all species. In all cases, ventricular strips showed a decrease in the force of contraction with sodium cyanide (NaCN) treatment. Ventricular strips from two Amazonian and one north temperate-zone species showed signs of recovery from NaCN treatment. There was considerable diversity in the ability of ventricular strips to develop force under conditions of impaired oxidative phosphorylation that was not related to the ability to obtain oxygen from the air or to geographic location. However, there was a major difference between Amazonian and north temperate-zone species in the ability of ventricular strips to maintain resting tension under NaCN treatment. Resting tension increased under conditions of simulated anoxia in ventricular strips from all north-temperate-zone species, but there was no change in resting tension in ventricular strips from Amazonian species. We propose that hearts from the Amazonian species are better able to reduce cytoplasmic calcium levels, possibly through a more highly developed sarcoplasmic reticulum.