Cardiac function of two ecologically distinct Neotropical freshwater fish: Curimbata, Prochilodus lineatus (Teleostei, Prochilodontidae), and trahira, Hoplias malabaricus (Teleostei, Erythrinidae)

An isometric muscle preparation was used to investigate the importance of the ventricular sarcoplasmic reticulum (SR) and extracellular Ca2+ (2.5 up to 10.5 mM) to force generation at 25 °C (acclimation temperature) in two ecologically distinct Neotropical teleost fish: Curimbata (active species), and trahira (sedentary species). The post-rest force was studied with and without 10 μM ryanodine in the medium. The positive inotropism observed for both species in response to increases on extracellular Ca2+ reflected a greater Ca2+ influx through sarcolemma, as well as an increase in Ca2+ liberation from the SR by the Ca2+-induced Ca2+ release mechanism. The significant post-rest potentiation recorded for the curimbata and trahira control preparations (3.22 ± 0.24 to 6.55 ± 0.77 mN mm− 2 and 0.74 ± 0.07 to 2.26 ± 0.26 mN mm− 2, respectively), was completely inhibited by the addition of ryanodine to the bathing medium, suggesting a potential functionality of SR for both species. Considering the differences in these species habitats, modes of life and levels of activity and the fact of a probable SR Ca2+ cycling in a physiological temperature, we suggest that the functionality of the SR in these species is probably related to their phylogeny.