Meeting Abstract
In many teleosts, oxygen (O2) and carbon dioxide (CO2) transport are tightly coupled due to the presence of Root effect hemoglobin (Hb), whereby reduced pH dramatically reduces binding affinity and capacity for O2. Previous work demonstrates that the evolution of Root effect Hb in teleosts coincided with the incorporation of high-activity carbonic anhydrase into the red blood cell (RBC CA). In most vertebrates, the role of RBC CA is thought to be exclusively related to CO2 transport and excretion, as it is responsible for catalyzing the reversible dehydration/hydration reactions of CO2. However, RBC CA also dictates the rate of red blood cell acidification during capillary transport, which impacts the relationship between Hb and O2. Thus, high-activity RBC CA may be an important, previously unknown component of enhanced tissue O2 delivery in teleosts that contain Root effect Hb. We have developed an in vitro assay using lysed red blood cells that allows us to manipulate RBC CA activity while simultaneously measuring O2 offloading following CO2 injection. 50% RBC CA inhibition significantly decreased oxygen delivery rate (p = 0.0196, Student’s t-test) by 50%, demonstrating an almost 1:1 relationship between RBC CA activity and oxygen delivery rate. Additionally, we found that across a ten-fold range in body mass, the allometric scaling of RBC CA activity demonstrates a relationship much like that of standard and maximum metabolic rate. This suggests individuals with higher oxygen demands have higher RBC CA activity. Combined, our data suggest RBC CA dictates O2 delivery in conjunction with its characteristic role in CO2 excretion, expanding its function in respiratory gas exchange for the first time in almost 90 years.
