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Functional properties of primitive and definitive red cells from chick embryo: oxygen-binding characteristics, pH and
Insights
Primitive and definitive red blood cells share properties, with definitive cells adapting to hypoxia. Oxygen pressure influences definitive cell differentiation, mediated by high molecular weight plasma factors.
Area of Science:
- Hematology
- Developmental Biology
- Red Blood Cell Physiology
Background:
- Primitive and definitive red blood cells exhibit distinct characteristics during development.
- Understanding red blood cell properties is crucial for embryonic development and oxygen transport.
Purpose of the Study:
- Compare properties of primitive and definitive red blood cells.
- Investigate the effect of hemoglobin patterns on oxygen affinity.
- Analyze cellular response to hypoxia and red cell membrane potential/pH.
Main Methods:
- Comparative analysis of red blood cell properties.
- Measurement of oxygen-binding curves and hemoglobin patterns.
- Assessment of cellular response to hypoxia, including phosphate patterns and enzyme activity.
Main Results:
- Definitive red blood cells share properties with primitive cells, with similar oxygen-binding curves initially.
- Significant increase in oxygen affinity in definitive red cells between days 7-14.
- Hypoxia induces coordinated changes in definitive but not primitive red cells.
- Membrane potential transitions from proton diffusion to Donnan equilibrium.
Conclusions:
- Oxygen pressure regulates definitive red blood cell differentiation via plasma factors.
- Red cell pH is maintained, facilitating embryonic oxygen affinity adjustment.
- Developmental changes in red cell membrane potential and ion distribution are critical.
Abstract:
We compare properties of primitive and definitive red cells in three areas effect of different hemoglobin patterns on oxygen affinity cellular response to hypoxia, and red cell membrane potential and cell pH since during incubation blood pH decreases by 0.5 pH. We find that the first population of definitive red cells has many properties in common with the preceding primitive red cells. The oxygen-binding curves are nearly identical despite the fact that the definitive red cells contain only the adult hemoglobins A and D; in particular, n values greater than 4 are recorded in the upper saturation range. Within the definitive red cell population there is a drastic increase in the oxygen affinity between days 7 to 14. Hypoxia causes a series of coordinated changes in definitive but not primitive red cells, involving the phosphate pattern (2,3 DPG, ATP) as well as changes of carbonic anhydrase activity and oxygen affinity. The results suggest that the oxygen pressure controls part of the differentiation program of the definitive cell population and that control is dependent on plasma factors of high molecular weight. The membrane potential of primitive and early definitive red cells is a proton diffusion potential. During development proton conductivity decreases, and at day 16 proton and chloride distribution can be adequately described by the Donnan equilibrium. The linkage between membrane potential and proton distribution allows maintenance of red cell pH at about 7.2, irrespective of external pH, which greatly facilitates the adjustment of embryonic oxygen affinity.