Differential effects of bicarbonate on severe hypoxia- and hypercapnia-induced cardiac malfunctions in diverse fish spec
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ORIGINAL PAPER
Differential effects of bicarbonate on severe hypoxia‑ and hypercapnia‑induced cardiac malfunctions in diverse fish species Mandy Lo1 · Arash Shahriari1 · Jinae N. Roa2 · Martin Tresguerres2 · Anthony P. Farrell1,3 Received: 7 July 2020 / Revised: 6 October 2020 / Accepted: 28 October 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract We tested in six fish species [Pacific lamprey (Lampetra richardsoni), Pacific spiny dogfish (Squalus suckleyi), Asian swamp eel (Monopterus albus), white sturgeon (Acipenser transmontanus), zebrafish (Danio rerio), and starry flounder (Platichthys stellatus)] the hypothesis that elevated extracellular [ HCO3−] protects spontaneous heart rate and cardiac force development from the known impairments that severe hypoxia and hypercapnic acidosis can induce. Hearts were exposed in vitro to either severe hypoxia (~ 3% of air saturation), or severe hypercapnic acidosis (either 7.5% CO2 or 15% CO2), which reduced heart rate (in six test species) and net force development (in three test species). During hypoxia, heart rate was restored by [HCO3−] in a dose-dependent fashion in lamprey, dogfish and eel (EC50 = 5, 25 and 30 mM, respectively), but not in sturgeon, zebrafish or flounder. During hypercapnia, elevated [HCO3−] completely restored heart rate in dogfish, eel and sturgeon (EC50 = 5, 25 and 30 mM, respectively), had a partial effect in lamprey and zebrafish, and had no effect in flounder. Elevated [HCO3−], however, had no significant effect on net force of electrically paced ventricular strips from dogfish, eel and flounder during hypoxia and hypercapnia. Only in lamprey hearts did a specific soluble adenylyl cyclase (sAC) inhibitor, KH7, block the HCO3−-mediated rescue of heart rate during both hypoxia and hypercapnia, and was the only species where we conclusively demonstrated sAC activity was involved in the protective effects of H CO3− on cardiac function. Our results − suggest a common H CO3 -dependent, sAC-dependent transduction pathway for heart rate recovery exists in cyclostomes and a HCO3−-dependent, sAC-independent pathway exists in other fish species. Keywords Bicarbonate ions · Cardiac contractility · Heart rate · Hypercapnia tolerance · Hypoxia tolerance · Soluble adenylyl cyclase
Introduction Communicated by Bernd Pelster. Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00360-020-01324-y) contains supplementary material, which is available to authorized users. * Mandy Lo [email protected] 1
Department of Zoology, University of British Columbia, 6270 University Boulevard, Vancouver, BC V6T 1Z4, Canada
2
Marine Biology Research Division, Scripps Institution of Oceanography, University of California San Diego, 9500 Gilman Drive, La Jolla, CA 92093, USA
3
Faculty of Land and Food Systems, University of British Columbia, 2357 Main Mall, Vancouver, BC V6T 1Z4, Canada
Severe hypoxia and hypercapnic acidosis, which can exist in nature, are known to sev
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