Effects of change in temperature on the cardiac contractility of broad‐snouted caiman (Caiman latirostris) during digestion

Abstract

In many reptiles, digestion has been associated with the selection of higher body temperatures, the so‐called post‐prandial thermophilic response. This study aimed to investigate the excitation–contraction (E–C) coupling in postprandial broad‐snouted caimans (Caiman latirostris) in response to acute warming within a preferred body temperature range of crocodiles. Isometric preparations subjected to a temperature transition from 25°C to 30°C were used to investigate myocardial contractility of postprandial caimans, that is, 48 h after the animals ingested a rodent meal corresponding to 15% of body mass. The caiman heart exhibits a negative force–frequency relationship that is independent of the temperature. At 25°C, cardiac muscle was able to maintain a constant force up to 36 bpm, above which it decreased significantly, reaching minimum values at the highest frequency of 84 bpm. Moreover, E–C coupling is predominantly dependent on transsarcolemmal Ca2+ transport denoted by the lack of significant ryanodine effects on force generation. On the contrary, ventricular strips at 30°C were able to sustain the cardiac contractility at higher pacing frequencies (from 12 to 144 bpm) due to an important role of Na+/Ca2+ exchanger in Ca2+ cycling, as indicated by the decay of the post‐rest contraction, and a significant contribution of the sarcoplasmic reticulum above 72 bpm. Our results demonstrated that the myocardium of postprandial caimans exhibits a significant degree of thermal plasticity of E–C coupling during acute warming. Therefore, myocardial contractility can be maximized when postprandial broad‐snouted caimans select higher body temperatures (preferred temperature zone) following feeding.