Mass Transport: Circulatory System with Emphasis on Nonendothermic Species

Mass transport can be generally defined as movement of material matter. The circulatory system then is a biological example given its role in the movement in transporting gases, nutrients, wastes, and chemical signals. Comparative physiology has a long history of providing new insights and advancing our understanding of circulatory mass transport across a wide array of circulatory systems. Here we focus on circulatory function of nonmodel species. Invertebrates possess diverse convection systems; that at the most complex generate pressures and perform at a level comparable to vertebrates. Many invertebrates actively modulate cardiovascular function using neuronal, neurohormonal, and skeletal muscle activity. In vertebrates, our understanding of cardiac morphology, cardiomyocyte function, and contractile protein regulation by Ca2+ highlights a high degree of conservation, but differences between species exist and are coupled to variable environments and body temperatures. Key regulators of vertebrate cardiac function and systemic blood pressure include the autonomic nervous system, hormones, and ventricular filling. Further chemical factors regulating cardiovascular function include adenosine, natriuretic peptides, arginine vasotocin, endothelin 1, bradykinin, histamine, nitric oxide, and hydrogen sulfide, to name but a few. Diverse vascular morphologies and the regulation of blood flow in the coronary and cerebral circulations are also apparent in nonmammalian species. Dynamic adjustments of cardiovascular function are associated with exercise on land, flying at high altitude, prolonged dives by marine mammals, and unique morphology, such as the giraffe. Future studies should address limits of gas exchange and convective transport, the evolution of high arterial pressure across diverse taxa, and the importance of the cardiovascular system adaptations to extreme environments. © 2017 American Physiological Society. Compr Physiol 7:17-66, 2017.

Modulatory mechanisms in the isolated internally perfused ventricle of the whelk Busycon canaliculatum

1. Isolated cannulated ventricles commenced spontaneous beating on application of perfusion pressure of 10 cm water. Complete hearts showed a fast patterned cyclical rhythm, whereas ventricles devoid of atrial material showed a continuous slow rhythm. 2. Perfused ventricles were inhibited by ACh with a threshold at 10(-8) mol l-1 and arrested at 10(-7) mol l-1, and ventricles under stimulation by 5HT could be arrested by ACh at this concentration. 3. Perfused ventricles were stimulated by 5HT, with threshold at 10(-9) mol l-1 and maximum at 10(-5) mol l-1. Metoclopramide was without affect on 5HT responses, but metitipine and methysergide did inhibit such responses suggesting that the 5HT receptor present possessed mixed properties of the vertebrate 5-HT1 and 5-HT2 receptor subtypes. 4. Ventricles were very sensitive to the excitatory actions of FMRFamide in the 10(-9) to 10(-5) mol l-1 range. Preparations were insensitive to GAPFLRFamide, but SCP-B was modestly excitatory (threshold 10(-7) mol l-1). 5. Preparations were not significantly affected by adenosine, ATP, and guanosine, but GTP was strongly excitatory at 10(-7) mol l-1. 6. 5HT and FMRFamide responses were additive. Preparations responded strongly to the adenylate cyclase activator forskolin and dibutyryl cAMP enhanced spontaneous contractions and 5HT responses, suggesting that the 5HT receptor may operate via a cAMP secondary mechanism. 7. The IP3 inhibitor lithium (10 mmol l-1), caused slight inhibition of FMRFamide responses, suggesting that the receptor to this peptide may operate via IP3 as a second messenger. 8. Neuromodulation in this preparation would appear to involve ACh as inhibitor, 5HT and FMRFamide as upregulators, with no clear roles for FMRFamide-related peptides and GTP.