Membrane potential of primitive red cells from chick embryo is a proton potential.

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.