title: Tolerance of acute hypercapnic acidosis by the European eel ( Anguilla anguilla).
abstract: European eels ( Anguilla anguilla) were exposed sequentially to partial pressures of CO(2) in the water ( PwCO(2)) of 5, 10, 20, 40, 60 then 80 mm Hg (equivalent to 0.66-10.5 kPa), for 30 min at each level. This caused a profound drop in arterial plasma pH, from 7.9 to below 7.2, an increase in arterial PCO(2) from 3.0 mm Hg to 44 mm Hg, and a progressive decline in arterial blood O(2) content (caO(2)) from 10.0% to 1.97% volume. Gill ventilation rate increased significantly at water PwCO(2)s of 10, 20 and 40 mm Hg, followed by a decline at PwCO(2)s of 60 and 80 mm Hg, due to periodic breathing. Mean opercular pressure amplitude increased steadily throughout hypercapnic exposure and was significantly elevated at a PwCO(2) of 80 mm Hg. Hypercapnia caused a tachycardia between PwCO(2)s of 5 mmHg and 10 mm Hg, followed by a progressive decline in heart rate. Cardiac output (CO) remained unchanged throughout, as a consequence of a significant increase in stroke volume at PwCO(2)s of 40, 60 and 80 mm Hg. The eels maintained O(2) uptake at routine normocapnic levels throughout hypercapnic exposure. A comparison of the rates of blood O(2) delivery (calculated from CO and caO(2)) against O(2) consumption at PwCO(2)s of 60 mm Hg and 80 mm Hg indicated that a portion of O(2) uptake was due to cutaneous respiration. Thus, the European eel's exceptional tolerance of acute hypercapnia is probably a consequence of the tolerance of its heart to acidosis and hypoxia, and a contribution to O(2) uptake from cutaneous respiration.
authors.affiliation: School of Biosciences, University of Birmingham, United Kingdom. mckenzie@cesi.it
authors.forename: D J
authors.initials: DJ
authors.lastname: McKenzie
authors.forename: E W
authors.initials: EW
authors.lastname: Taylor
authors.forename: A Z
authors.initials: AZ
authors.lastname: Dalla Valle
authors.forename: J F
authors.initials: JF
authors.lastname: Steffensen
mesh_terms: D000136:Acid-Base Equilibrium / Q000502:physiology; D000142:Acidosis, Respiratory / Q000503:physiopathology*; D000811:Anguilla / Q000502:physiology*; D000818:Animals; D002245:Carbon Dioxide / Q000097:blood; D002302:Cardiac Output / Q000502:physiology; D005060:Europe; D006935:Hypercapnia / Q000503:physiopathology*; D010100:Oxygen / Q000097:blood; D010101:Oxygen Consumption / Q000502:physiology; D012119:Respiration
chemical_list: D002245:Carbon Dioxide; D010100:Oxygen