Control of Branchial Artery Tone in Fish: Effects of Environmental Temperature and Phylogeny

Branchial artery vasoreactivity and nerve density were measured in teleosts of different phylogenetic relatedness from cold (-1.86 degrees to -1 degrees C) and temperate (similar to 13 degrees C) environments. Polar Notothenia coriiceps and temperate Paranotothenia angustata are closely related Southern Hemisphere nototheniids, and polar Boreogadus saida and temperate Myoxocephalus scorpius are Northern Hemisphere species that are phylogenetically distant from each other and the nototheniids. Rainbow trout Oncorhynchus mykiss was used as a temperate comparison of different activity patterns. Cumulative dose-response curves for efferent branchial arteries (EBAs) revealed a lack of alpha-adrenergic (noradrenaline [NOR]) vasoactivity in M. scorpius and a lack of cholinergic (carbachol [CARB]) vasoactivity in B. saida, while responses in N. coriiceps and P. angustata were irregular. Oncorhynchus mykiss vessels were responsive to both constrictors, suggesting either receptor absence or spatial heterogeneity among species. The sensitivity (pEC(50)) of NOR or 5-hydroxytryptamine (5-HT) vasoconstriction showed little interspecific variation, while maximal tension varied among species for NOR but not 5-HT. Acute cooling did not affect agonist-independent vascular contraction induced by KCl or in response to NOR or 5-HT. The CARB sensitivity of EBAs increased with cooling in P. angustata alone. Each species possessed a unique pattern of innervation on both branchial arteries, distal and proximal to their respective aortas, that partially differentiated between nototheniids and nonnototheniids. We conclude there is little evidence for cold adaptation of branchial artery contractility, and mechanisms of vascular control likely reflect phylogeny rather than thermal history.