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The evolution of Root effect hemoglobins in the absence of intracellular pH protection of the red blood cell: insights from primitive fishes

Synopsis:

What we did: The Root effect is a reduction in haemoglobin-oxygen binding affinity with low pH that is used by most fish species to deliver large quantities of oxygen to the swimbladder and eye. In this study, we explored various Root effect characteristics in the haemoglobins of seven primitive fish species to better understand how this system evolved without jeopardizing oxygen uptake at the gill.

What we found: The seven primitive fish species each possessed a Root effect of some magnitude, but these Root effects were each induced at pH values lower than would naturally occur in the blood of these species.

What this means: These primitive species’ Root effect onset pH values are too low to jeopardize oxygen uptake at the gill. While this means the Root effect has no negative impact on these fish following hypoxia- and exercise-induced generalized blood acidoses, it also implies that these Root effects are unusable by some of these fish (the four most primitive species; see accompanying paper) and perhaps a property only observed under certain experimental conditions. This affects current thinking on how this system evolved.