Efeitos do exercício prolongado sobre a contratilidade cardíaca de uma espécie de peixe migratória, Brycon amazonicus (Teleostei, Characidae)

Abstract

The present work described the effects of exercise-training (60 days) at different intensities 5 cm.s-1 (EL), 10 cm.s-1 (EM), 20 cm.s-1 (EMI) and 30 cm.s -1 (EI) on relative ventricular mass (RVM), in vitro ventricular contractility and proteins expression of excitation-contraction coupling proteins in the ventricular tissue of Brycon amazonicus, a very active fish species with migratory habits. The majority of exercise intensities did not alter the RVM, except for the EMI group where a reduction was observed in relation to its respective CT group. EL and EM groups presented more relevant increases on ventricular force generation, suggesting that the studied species show different adaptations in the capacity of contractile force generation (Fc) in the following the exercise intensity. It may be suggested that conditions imposed by the rigorous exercise protocols (EMI and EI groups) did not cause improvements in contractile performance. The present results indicate that all groups exhibited modulations of the E-C coupling components. The Ca2+ influx via NCX was important in all groups, and the relative role of RS varied considerably between groups. In EL group, the RS contribution was essential for the force generation under a wide range of estimation frequencies (0.2-1.8Hz) whereas in the RS and EM and EMI groups the RS action was only relevant at high frequencies (1.0-1.8Hz). In the EI group, the functional inhibition of RS did not cause reductions in Fc values in all analyzes frequencies, indicating that the LTCCs and the NCX took the lead during the force generation. In addition, the exercise protocols triggered different expression rates of the E-C coupling components. The EL group presented higher NCX expression rates and lower SERCA2 rates but did not alter PLB expression. The EM group presented higher expression rates of NCX and PLB, and lower SERCA2 rates. Both EMI and EI exhibited elevations in the LTCCs, NCX and SERCA2 expression rates but did not alter the PLB expression. The data generated in the present work revealed that the ventricular E-C coupling of B. amazonicus presents great plasticity in response to the exercise, modulating the relative roles of its components in accordance with the intensity of the exercise training.