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Osmoregulatory bicarbonate secretion exploits H+-sensitive haemoglobins to autoregulate intestinal O2 delivery in euryhaline teleosts

Synopsis:

What we did: We investigated whether a special type of fish haemoglobin that is capable of offloading large amounts of oxygen through the binding of protons (called a Root effect haemoglobin) plays an indirect role in how fish (flounder in this case) in hypersaline water use their intestinal cells to balance ions.

What we found: Flounder’s blood pH and haemoglobin properties enhance O2 delivery to the intestinal cells by up to 42% according to our mathematical models.

What this means: The mechanism marine fishes use to balance divalent ions such as calcium depends on metabolically produced CO2 in the intestinal cells. A haemoglobin molecule that significantly enhances O2 delivery to these cells equally enhances their ability to produce CO2. Therefore, these Root effect haemoglobins improve the fish’s ability to regulate divalent ions, which helps enable their survival in hypersaline waters rich in these ions.