Resting and maximal heart rates in ectothermic vertebrates

Area of Science:

• Comparative physiology
• Cardiovascular biology
• Ectotherm research

Background:

• Heart rates (HR) in ectotherms are typically lower than in endotherms, varying significantly across species.
• HR is influenced by temperature, activity, gas exchange, and neural/hormonal factors.
• Intrinsic pacemaker rates are modulated by cholinergic and adrenergic systems, with neuropeptides also playing a role.

Purpose of the Study:

• To explore the determinants of resting and maximal heart rates in ectothermic vertebrates.
• To understand the influence of temperature and other physiological factors on cardiac function.
• To examine the evolutionary pressures shaping heart rate regulation.

Main Methods:

• Comparative analysis of heart rate data across diverse ectothermic species.
• Review of physiological and molecular mechanisms influencing cardiac function.
• Examination of environmental and metabolic factors affecting heart rate.

Main Results:

• Resting and maximal HRs in ectotherms are lower than in endotherms, with wide interspecific variation.
• Temperature, metabolic rate, and hemodynamic needs are primary determinants of resting HR.
• Maximal HRs are generally below 120 bpm, with exceptions like tuna and small reptiles exceeding 300 bpm at high temperatures.

Conclusions:

• Temperature significantly impacts intrinsic pacemaker rates and autonomic modulation of HR in ectotherms.
• Evolutionary selection pressures for rapid cardiac rates are linked to hemodynamic and oxygen requirements.
• Factors like pacemaker potential, calcium handling, cell coupling, and coronary circulation influence maximal HR capabilities.