The effects of hypoxic bradycardia and extracellular HCO3-/CO2 on hypoxic performance in the eel heart

• Published in: Journal of Experimental Biology
• Main Authors: Joyce, William, Simonsen, Maj, Gesser, Hans, Wang, Tobias
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2016
• Subjects: Heart rate; Myocardial hypoxia; Contractility; Anguilla anguilla; TROUT ONCORHYNCHUS-MYKISS; RAINBOW-TROUT; REFLEX BRADYCARDIA; ANGUILLA-ANGUILLA; FORCE; FISH; TOLERANCE; ACIDOSIS; CARP
• Online Access: https://pure.au.dk/portal/en/publications/81bd1928-6bee-4a2d-8380-8740f5e8d5c6; https://doi.org/10.1242/jeb.130971; https://pure.au.dk/ws/files/119286038/302.full.pdf; http://www.scopus.com/inward/record.url?scp=84962611495&partnerID=8YFLogxK

During hypoxia, fishes exhibit a characteristic hypoxic bradycardia, the functional significance of which remains debated. Here, we investigated the hypothesis that hypoxic bradycardia primarily safeguards cardiac performance. In preparations from the European eel (Anguilla anguilla), a decrease in stimulation frequency from 40 to 15 beats min -1 , which replicates hypoxic bradycardia in vivo, vastly improved cardiac performance during hypoxia in vitro. As eels display dramatic shifts in extracellular HCO 3 - /CO 2 , we further investigated the effect this has upon hypoxic cardiac performance. Elevations from 10 mmol l -1 HCO 3 - /1% CO 2 to 40 mmol l -1 HCO 3 - /4% CO 2 had few effects on performance; however, further, but still physiologically relevant, increases to 70 mmol l -1 HCO 3 - /7% CO 2 compromised hypoxia tolerance. We revealed a four-way interaction between HCO 3 - /CO 2 , contraction frequency, hypoxia and performance over time, whereby the benefit of hypoxic bradycardia was most prolonged at 10 mmol l -1 HCO 3 - /1% CO 2 . Together, our data suggest that hypoxic bradycardia greatly benefits cardiac performance, but its significance may be context specific.