Red blood cell carbonic anhydrase mediates oxygen delivery via the Root effect in red drum

• Published in: Journal of Experimental Biology
• Main Authors: Dichiera, Angelina M., Esbaugh, Andrew J.
• Format: Text
• Language: English
• Published: The Company of Biologists Ltd 2020
• Subjects: RESEARCH ARTICLE; Red drum; Sciaenops ocellatus
• Online Access: http://jeb.biologists.org/cgi/content/short/223/22/jeb232991; https://doi.org/10.1242/jeb.232991

Oxygen (O 2 ) and carbon dioxide (CO 2 ) transport are tightly coupled in many fishes as a result of the presence of Root effect hemoglobins (Hb), whereby reduced pH reduces O 2 binding even at high O 2 tensions. Red blood cell carbonic anhydrase (RBC CA) activity limits the rate of intracellular acidification, yet its role in O 2 delivery has been downplayed. We developed an in vitro assay to manipulate RBC CA activity while measuring Hb-O 2 offloading following a physiologically relevant CO 2 -induced acidification. RBC CA activity in red drum ( Sciaenops ocellatus ) was inhibited with ethoxzolamide by 53.7±0.5%, which prompted a significant reduction in O 2 offloading rate by 54.3±5.4% ( P= 0.0206, two-tailed paired t -test; n =7). Conversely, a 2.03-fold increase in RBC CA activity prompted a 2.14-fold increase in O 2 offloading rate ( P <0.001, two-tailed paired t -test; n= 8). This approximately 1:1 relationship between RBC CA activity and Hb-O 2 offloading rate coincided with a similar allometric scaling exponent for RBC CA activity and maximum metabolic rate. Together, our data suggest that RBC CA is rate limiting for O 2 delivery in red drum.