Department of Physiological Sciences, Federal University of São Carlos, São Carlos, São Paulo, Brazil.
Joint Graduate Program in Physiological Sciences, Federal University of São Carlos-UFSCar/São Paulo State University, UNESP Campus Araraquara, Araraquara, São Paulo, Brazil.
J Exp Zool A Ecol Integr Physiol. 2021 Apr;335(4):417-425. doi: 10.1002/jez.2457. Epub 2021 Mar 26.
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 Ca 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 /Ca exchanger in Ca 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.
在许多爬行动物中，消化与选择较高的体温有关，即所谓的餐后热嗜反应。本研究旨在调查餐后宽吻凯门鳄（Caiman latirostris）在进食后 48 小时内，在鳄鱼的最佳体温范围内，对急性升温的兴奋-收缩（E-C）偶联。使用从 25°C 过渡到 30°C 的等长制剂来研究餐后凯门鳄的心肌收缩性，即动物摄入相当于其体重 15%的啮齿动物餐 48 小时后。凯门鳄心脏表现出与温度无关的负力频率关系。在 25°C 时，心肌能够在 36 bpm 以下保持恒定的力，超过该频率，力显著下降，在最高频率 84 bpm 时达到最小值。此外，E-C 偶联主要依赖于跨肌膜 Ca 转运，这表明缺乏对力产生有显著影响的肌浆网钙释放通道激动剂。相反，在 30°C 时，心室条带能够在较高的起搏频率（从 12 到 144 bpm）下维持心脏收缩性，这是由于 Na+/Ca 交换在 Ca 循环中的重要作用，如后收缩衰减所表明的，以及肌浆网在 72 bpm 以上的显著贡献。我们的研究结果表明，餐后宽吻凯门鳄的心肌在急性升温期间表现出 E-C 偶联的显著热塑性。因此，当宽吻凯门鳄在进食后选择较高的体温（最佳温度区）时，心肌收缩性可以最大化。
