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Membrane potential of primitive red cells from chick embryo is a proton potential
M Engelke1, W Zingel, R Baumann
1Zentrum Physiologie, Medizinische Hochschule Hannover, Hannover, Federal Republic of Germany.
Insights
Primitive red blood cells in chick embryos generate membrane potential primarily through proton conductance, not chloride, differing significantly from adult cells. This electrogenic H+ activity is crucial for early cell function.
Area of Science:
- Cellular Physiology
- Developmental Biology
- Biophysics
Background:
- The membrane potential of red blood cells is critical for cellular function.
- Understanding the mechanisms of membrane potential generation in embryonic cells is essential for developmental biology.
Purpose of the Study:
- To determine the membrane potential of primitive red cells in chick embryos.
- To investigate the ionic basis of membrane potential in these early cells.
- To compare embryonic red cell membrane potential mechanisms with those of adult cells.
Main Methods:
- Utilized the fluorescent dye Dis-C3-(5) to measure membrane potential in embryonic chick red cells.
- Performed experiments varying external ion concentrations (potassium, sodium, chloride).
- Assessed the effect of the anion exchange inhibitor DIDS and the Cl-/OH- exchanger tributyltin.
Main Results:
- Embryonic red cells exhibited a membrane potential of -44 mV at day 4 and -36 mV at day 6, distinct from chloride equilibrium potential.
- External ion concentration changes had minimal impact, except for high potassium concentrations causing depolarization.
- Evidence strongly suggests electrogenic H+ conductance as the primary driver of membrane potential, supported by proton equilibrium potential, tributyltin effects, and proton flux measurements.
Conclusions:
- The membrane potential in primitive chick red cells is mainly established by electrogenic proton (H+) conductance.
- Significant qualitative differences exist in membrane potential generation and hydrogen distribution between embryonic and adult chicken red cells.
Abstract:
The membrane potential of primitive red cells from 4- and 6-day old chick embryos has been determined using the fluorescent dye Dis-C3-(5). At day 4 the membrane potential Em was -44 mV for pH 7.4 and 20 degrees C and -36 mV at day 6. Both values are far removed from the equilibrium potential for chloride, which is about -14 mV at day 6. Changes in the external potassium, sodium or chloride concentration were without effect on the membrane potential, except at very high potassium concentrations, where a small but significant depolarization was observed at day 6. The measurements gave the same results in the absence or presence of the anion exchange blocking agent DIDS. Three pieces of evidence indicate that the membrane potential of primitive red cells is primarily caused by an electrogenic H+ conductance: 1) The measured membrane potential of -36 mV at day 6 is close to the previously determined proton equilibrium potential (Baumann and Haller, 1983) EH + of -36 mV. 2) Addition of the electrosilent Cl-/OH- exchanger tributyltin causes a significant depolarization of about 20 mV at day 4 and about 14 mV at day 6. 3) Measurement of hydrogen ion fluxes demonstrate a potential dependent proton conductance, which increases with depolarization. These results indicate that large qualitative differences exist with regard to the mechanisms involved in the generation of membrane potential and hydrogen distribution between red cell and plasma of embryonic and adult chicken.