Time course of red blood cell intracellular pH recovery following short-circuiting in relation to venous transit times in rainbow trout, Oncorhynchus mykiss

Am J Physiol Regul Integr Comp Physiol. 2018 Aug 1;315(2):R397-R407. doi: 10.1152/ajpregu.00062.2018. Epub 2018 Apr 11.


Accumulating evidence is highlighting the importance of a system of enhanced hemoglobin-oxygen (Hb-O2) unloading for cardiovascular O2 transport in teleosts. Adrenergically stimulated sodium-proton exchangers (β-NHE) create H+ gradients across the red blood cell (RBC) membrane that are short-circuited in the presence of plasma-accessible carbonic anhydrase (paCA) at the tissues; the result is a large arterial-venous pH shift that greatly enhances O2 unloading from pH-sensitive Hb. However, RBC intracellular pH (pHi) must recover during venous transit (31-90 s) to enable O2 loading at the gills. The halftimes ( t1/2) and magnitudes of RBC β-adrenergic stimulation, short-circuiting with paCA and recovery of RBC pHi, were assessed in vitro, on rainbow trout whole blood, and using changes in closed-system partial pressure of O2 as a sensitive indicator for changes in RBC pHi. In addition, the recovery rate of RBC pHi was assessed in a continuous-flow apparatus that more closely mimics RBC transit through the circulation. Results indicate that: 1) the t1/2 of β-NHE short-circuiting is likely within the residence time of blood in the capillaries, 2) the t1/2 of RBC pHi recovery is 17 s and within the time of RBC venous transit, and 3) after short-circuiting, RBCs reestablish the initial H+ gradient across the membrane and can potentially undergo repeated cycles of short-circuiting and recovery. Thus, teleosts have evolved a system that greatly enhances O2 unloading from pH-sensitive Hb at the tissues, while protecting O2 loading at the gills; the resulting increase in O2 transport per unit of blood flow may enable the tremendous athletic ability of salmonids.

Keywords: Bohr effect; hemoglobin; plasma-accessible carbonic anhydrase; teleost; β-NHE.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adrenergic beta-Agonists / pharmacology
  • Animals
  • Blood Flow Velocity
  • Carbonic Anhydrases / blood
  • Erythrocytes / drug effects
  • Erythrocytes / physiology*
  • Hydrogen-Ion Concentration
  • Isoproterenol / pharmacology
  • Models, Biological
  • Oncorhynchus mykiss / blood*
  • Oxygen / blood*
  • Oxyhemoglobins / metabolism
  • Regional Blood Flow
  • Sodium-Hydrogen Exchangers / blood
  • Time Factors
  • Veins / physiology*


  • Adrenergic beta-Agonists
  • Oxyhemoglobins
  • Sodium-Hydrogen Exchangers
  • Carbonic Anhydrases
  • Isoproterenol
  • Oxygen