H+ and Cl- ion equilibrium across the red cell membrane in the carp

Catecholamine-induced changes in oxygen affinity of carp and trout blood

Carp and trout blood maintained at low constant oxygen and carbon dioxide tensions was beta-stimulated. This activated the Na+/H(+)-exchanger of the red cell membrane, leading to increases in red cell pH (pHi) and cell water content, the latter resulting in dilution of hemoglobin and organic phosphates. The increase in pHi was rapid and maintained throughout the experimental period, the trout red cells showing the largest increase. Likewise swelling of the red cells was larger in trout than in carp blood. As a consequence of beta-stimulation the oxygen affinity of the blood increased. In trout the intracellular Bohr factor of unstimulated blood combined with the pHi increase upon stimulation could account for 85% of the increase in oxygen affinity, whereas it only covered 65% of the increase in carp blood. We therefore conclude that blood oxygen affinity is dependent on the red cell hemoglobin concentration in both species, the effect being more marked in carp.

CO2 transport in agnathan blood: evidence of erythrocyte Cl-/HCO3- exchange limitations

CO2 transport properties of blood were examined in the lamprey Petromyzon marinus and the hagfish Myxine glutinosa. In order to evaluate possible chloride/bicarbonate exchange limitations, experiments were conducted under control conditions and in the presence of an ionophore to permit equilibrium distribution of chloride, bicarbonate, and protons across the erythrocyte membrane. The ionophore, tri-n-propyl tin chloride, markedly altered the CO2 transport properties and apparent nonbicarbonate buffering characteristics of the blood of Petromyzon marinus. In addition, the distributions of protons, bicarbonate and chloride ions across the erythrocyte membrane were very different from each other under control conditions, but became very similar in the presence of the anionic ionophore. The CO2 transport properties of the blood of Myxine glutinosa were not significantly different in the presence of the ionophore. Small but significant changes were observed, however, in erythrocyte pH, chloride concentration and water content in the presence of tri-n-propyl tin chloride. These results demonstrate that chloride/bicarbonate exchange limitations and possibly active transport of protons contribute to the unique CO2 transport properties in the blood of the lamprey, Petromyzon marinus. In the hagfish, Myxine glutinosa, the importance of anion exchange limitations or active proton transport with regard to the CO2 carrying properties of the blood are clearly much less than in the lamprey under the in vitro conditions of this study.

Volume regulation in glutathione-treated brook trout (Salvelinus fontinalis) erythrocytes

Brook trout erythrocytes that were washed with and suspended in Ringer's solution with reduced glutathione (1.0 mM) maintained steady state cell volume for up to 24h, while those without the thiol-protective agent steadily shrank. Changes in cell volume (measured as packed cell volume, PCV) were evoked by acidic media (Ringer's at pH 6.8), hypoosmotic solutions (or both) and intracellular K(+) and Cl(-) concentrations were monitored over 4h. Acid-swollen cells failed to volume regulate or release K(+) but had significantly elevated intracellular Cl(-) Osmotically-swollen cells at pH 7.8 but not at pH 6.8 underwent regulatory volume decrease (RVD) and returned to initial levels in 2h, accompanied by release of K(+) and Cl(-) In contrast, osmotically-shrunken cells did not show regulatory volume increase. The regulatory volume decrease and concomitant K(+) release were dependent on Cl(-) implying a direct or indirect coupling of K(+) to Cl(-) transport in volume regulation. RVD was partially blocked by 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS, 0.1 mM), an anion exchange blocker, but was unaffected by amiloride (1.0 mM) which blocks Na(+)/H(+) exchange. Amiloride and DIDS prevented the swelling response to low pH but had no effect on control cells, suggesting involvement of Na(+)/H(+) and Cl(-)/HCO3 (-) exchanges in acid-induced cell swelling. Quinine (1.0 mM) a known blocker of K(+) channels, exacerbated the osmotically-induced swelling but had little effect on the subsequent RVD and release of KCl. The results suggest that low extracellular pH inhibits neutral C(-)-dependent K(+) release and the resultant regulatory volume decrease in osmotically-swollen cells.

Red-cell pH in tench. Interacting effects of cellular nucleoside triphosphates, Hb-oxygenation and extracellular pH

Experimental adjustments of red-cell pH (pHi) by varying red-cell nucleoside triphosphate (NTP) content, blood oxygenation state and extracellular pH (pHe) demonstrated a tight interdependence of these variables in their influence upon pHi. The increase in pHi with deoxygenation (delta pHi (d--o] is large, but becomes strongly reduced when the NTP content is decreased and when pHe falls. Lowering of red-cell NTP increases pHi, notably at high pHe, but this NTP dependence of pHi (delta pHi/delta(NTP/Hb] is much smaller in deoxygenated than in oxygenated blood. The pHe dependence of pHi (delta pHi/delta pHe) increases upon reduction of red-cell NTP content and upon deoxygenation. The results are consistent with the view that pHi is governed by Donnan-like distribution of protons across the red-cell membrane, and show that a pronounced red-cell swelling accompanies increases in the distribution ratio [H+]e/[H+]i. The data are interpreted in terms of changes in the red-cell non-permeable charge as induced by NTP and its linkage with the haemoglobin proton equilibria.

Blood oxygen equilibria and theoretical models. II. A critical estimation

1. Theoretical models can fit the oxygen equilibria of trout and human red cell suspensions, and describe the apparent oxygenation process in the red cell. 2. The assumption that full oxygenation is attained at atmospheric O2 pressures can result in biphasic Hill plots and high Hill coefficients for high O2 saturations. This phenomenon must not be confused with aggregation of hemoglobin. 3. Problems specific to measurements of red cell suspensions, regarding the ionic cellular composition and its stability with time, are approached. Changes of buffer osmolarity, and--for trout--addition of adrenaline, within physiological proportions, have no impact on the results. 4. This tends to validate the general significance of equilibrium data obtained on this material, regarding the effects of protons and organic phosphates, although complex ionic movements across the red cell membrane are known to occur in the animal under certain circumstances.

Pronounced influence of Hb-O2 saturation on red cell pH in tench blood in vivo and in vitro

At an extracellular pH of 7.9 the red cell pH in tench blood exhibits a nonlinear, strongly inverse relationship with Hb-O2 saturation, both when investigated in vitro and in vivo (in fish exposed to acid water with and without aluminium). The pHi difference between deoxygenated and oxygenated erythrocytes is large (i.e., 0.35 pH units), which can be accounted for by the Haldane effect and the buffering properties of the blood. The major shift in pHi occurs between 50 and 100% Hb-O2 saturation, indicating an almost full exploitation of the Haldane effect within the normal physiological range of blood O2 saturations.