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Matrinxã (Brycon amazonicus) is a great swimming performance teleost fish from the Amazon basin. However, the possible cardiac adaptations of this ability are still unknown. Therefore, the aim of the present work was to investigate the effects of prolonged exercise (EX group - 60days under 0.4BL·s -1 ) on ventricular contractility by (i) in-vitro analysis of contractility comparing the relative roles of sodium/calcium exchanger (NCX) and sarcoplasmic reticulum (SR) in the excitation-contraction (E-C) coupling and (ii) molecular analysis of NCX, sarcoplasmic reticulum Ca 2+ ATPase (SERCA2) and phospholamban (PLB) expression and quantification. The exercise training significantly improved twitch tension, cardiac pumping capacity and the contraction rate when compared to controls (CT). Inhibition of the NCX function, replacing Na + by Li + in the physiological solutions, diminished cardiac contractility in the EX group, reduced all analyzed parameters under both high and low stimulation frequencies. The SR blockage, using 10μM ryanodine, caused ~50% tension reduction in CT at most analyzed frequencies while in EX, reductions (34-54%) were only found at higher frequencies. SR inhibition also decreased contraction and relaxation rates in both groups. Additionally, higher post-rest contraction values were recorded for EX, indicating an increase in SR Ca 2+ loading. Higher NCX and PLB expression rates and lower SERCA2 rates were found in EX. Our data indicate that matrinxã presents a modulation in E-C coupling after exercise-training, enhancing the SR function under higher frequencies. This was the first study to functionally analyze the effects of swimming-induced exercise on fish cardiac E-C coupling., (Copyright © 2017 Elsevier Inc. All rights reserved.)

Glyphosate-based herbicides are widely used in agriculture and are commonly found in water bodies. Roundup Original(®) (RO) contains an isopropylamine glyphosate (GLY) salt containing the surfactant POEA, while Roundup Transorb R(®) (RTR) contains a potassium salt of GLY with unknown surfactants. Both contain different compositions of so-called "inert" ingredients, more toxic than glyphosate. Amphibian tadpoles often experience variations in O2 availability in their aquatic habitats; an ability to tolerate hypoxia can condition their survival and fitness. We evaluated the impacts of sublethal concentrations of GLY (1 mg L(-1)), RO (1 mg L(-1) GLY a.e) and RTR (1 mg L(-1) GLY a.e) on metabolic rate (V·O2 - mLO2 Kg1 h(-1)) of bullfrog tadpoles during normoxia and graded hypoxia, and related this to morphology of their skin, their major site of gas exchange. In control (CT) V·O2 remained unaltered from normoxia until 40 mmHg, indicating a critical O2 tension between 40 and 20 mmHg. GLY significantly reduced V·O2, possibly due to epidermal hypertrophy, which increased O2 diffusion distance to O2 uptake. In contrast, RTR increased V·O2 during hypoxia, indicating an influence of "inert" compounds and surfactants. V·O2 of RO did not differ from CT, suggesting that any increase in V·O2 caused by exposure was antagonized by epidermal hypertrophy. Indeed, all herbicides caused marked alterations in skin morphology, with cell and epithelium wall presenting hyperplasia or hypertrophy and chromatid rupture. In summary, GLY, RO and RTR exert different effects in bullfrog tadpoles, in particular the surfactants and inert compounds appear to influence oxygen uptake., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

This study evaluated if a concentration of 17α-ethinylestradiol (EE2 - 10 ng L(-1) for 96 h) normally found in Brazilian surface waters exerts any impact on cardiac function of bullfrog tadpoles (25 Gosner stage), Lithobates catesbeianus. During exposure, the animals' activity level (AL -% of active individuals) was monitored twice a day. Then, the in loco heart rate (f(H) - bpm) was determined, as well as the relative ventricular mass (RVM - % of body mass). Afterwards, cardiac ventricles were mounted for isometric force recordings (CS - mN mm(-2)), and determination of the cardiac pumping capacity (CPC - mN mm(-2) min(-1)). EE2 did not affect tadpoles' AL, although it resulted in a tachycardia in animals exposed to EE2 (f(H) = 66 bpm) when compared to controls (f(H) = 52 bpm), suggesting that EE2 acts directly on the cardiac muscle of tadpoles, rather than being a result of an increased cardiac demand due to a higher activity level (i.e., avoidance response). Additionally, EE2 exerted a positive inotropic response, which resulted in a higher CPC, which occurred independently of an increase in the number of myofibrils of EE2-exposed animals, since RVM remained similar between experimental groups. Thus, the increase on cardiac demand induced by the exposure to EE2 elevates considerably the animal energy expenditure, diverting a large amount of energy that tadpoles could use for their growth and development. These alterations can make amphibians more susceptible to predators and reduce the likelihood to reach reproductive stage., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

The chytrid fungus Batrachochytrium dendrobatidis (Bd) can result in heart failure in Bd-susceptible species. Since Bd infection generally does not cause mortality in North American bullfrogs, the aim of this work was to verify whether this species presents any cardiac adaptation that could improve the tolerance to the fungus. Thus, we analyzed tadpoles' activity level, relative ventricular mass, ventricle morphology, in loco heart frequency, and in vitro cardiac function. The results indicate that infected animals present an increase in both ventricular relative mass and in myofibrils' incidence, which accompanied the increase in myocytes' diameter. Such morphological alterations enabled an increase in the in vitro twitch force that, in vivo, would result in elevation of the cardiac stroke volume. This response requires much less energy expenditure than an elevation in heart frequency, but still enables the heart to pump a higher volume of blood per minute (i.e., an increase in cardiac output). As a consequence, the energy saved in the regulation of the cardiac function of Bd-infected tadpoles can be employed in other homeostatic adjustments to avoid the lethal effect of the fungus. Whether other species present this ability, and to what extent, remains uncertain, but such possible interspecific variability might explain different mortality rates among different species of Bd-infected amphibians., (© 2015 Wiley Periodicals, Inc.)

A drastic amphibian decline has been observed worldwide, which can be attributed (among other factors) to exposure to pollutants. Considering that cadmium corresponds to the most rapidly increasing trace metal in the environment, the aim of this work was to evaluate whether the exposure (2 and 16 days) of bullfrog tadpoles to this trace metal, at the concentration currently considered environmentally safe (at 1ppb) in class 1 and 2 waters by the Brazilian Environmental Council, can affect the cardiac performance of these animals. The acute exposure (2 days) of tadpoles to cadmium resulted in a marked bradycardic response, which was correlated with an incomplete cardiac relaxation, without any compensation by improved cardiac twitch force (Fc) or contraction velocity (TPT), nor even by cardiac hypertrophy. Indeed, after 16 days of exposure, the cardiac function of tadpoles became even more depressed due to a marked decrease in Fc, a prolongation of TPT, and also incomplete relaxation (i.e. increases in the ventricle resting tension), without changes in ventricle relative mass. Altogether, the cardiodepressive effects of cadmium (especially after more prolonged exposure periods) impose negative alterations on a tadpole׳s development and also impede adequate homeostatic adjustments to respond appropriately to the exposure to cadmium with increase in energetic demand to counteract the deleterious effects of the xenobiotic. These disturbances can impair tadpoles׳ growth, development and reproduction. It is a fact that allows us to strongly suggest that cadmium concentrations, which are currently considered environmentally safe in Brazil, should be revised., (Copyright © 2014 Elsevier Inc. All rights reserved.)