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

Erythropoiesis and red cell function in vertebrate embryos

All vertebrate embryos produce a specific erythroid cell population--primitive erythrocytes--early in development. These cells are characterized by expression of the specific embryonic haemoglobins. Many aspects of primitive erythropoiesis and the physiological function of primitive red cells are still enigmatic. Nevertheless, recent years have seen intensive efforts to characterize in greater detail the molecular events underlying the initiation of erythropoiesis in vertebrate embryos. Several key genes have been identified that are necessary for primitive and the subsequent definitive erythropoiesis, which differs in several aspect from primitive erythropoiesis. This review gives in its first part a short overview dealing with comparative aspects of primitive and early definitive erythropoiesis in higher and lower vertebrates and in the second part we discuss the physiological function of primitive red cells based mainly on results from mammalian and avian embryos.

Chloride and bicarbonate transport in chick embryonic red blood cells

1. Unidirectional efflux of 36Cl- and H14CO3- from erythrocytes of 4- to 16-day-old chick embryos was measured under steady-state conditions at 37 degrees C and pH 7.7. The efflux rates were high, > 3 s-1, and were, therefore, measured by means of the continuous flow tube method. 2. At day 4 of development the range of permeability coefficients for bicarbonate and chloride (PHCO3 and PCl was 1-30 x 10(-4) cm s-1, with average values of respectively 10 x 10(-4) and 8 x 10(-4) cm s-1. However, the results can be divided into two groups, one with PHCO3 and PCl above 12 x 10(-4) cm s-1, and one with values below 5 x 10(-4) cm s-1. The same range of values was also obtained for day 6 erythrocytes, but the overlap is more conspicuous. At day 16, PHCO3 and PCl were respectively 9 x 10(-4) and 6 x 10(-4) cm s-1 (37 degrees C, pH 7.7). In adult chicken red blood cells PHCO3 and PCl were respectively 7 x 10(-4) and 4 x 10(-4) cm s-1, and in human red blood cells the respective values were 5.6 x 10(-4) and 4 x 10(-4) cm s-1. 3. Chloride self-exchange, measured at 0 degrees C, was almost completely inhibited by addition of 1 mM 4,4'-diisothiocyanostilbene-2,2'-disulphonate (DIDS) at both days 6 and 16 of embryonic development, supporting the finding that the embryonic chick erythrocytes also have a transmembrane anion exchanger similar to that of other red cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Control of cell pH in immature primitive red cells from chick embryo

1. The intracellular pH in primitive red cells from 4 day chick embryos was measured with the digitonin null-point method and the fluorescent indicator SNARF-1. At physiological pHe of 8.0 red cell pH is 7.39 at day 4. 2. The calculated proton equilibrium potential of -38 mV is in good agreement with previous measurements of Em (Engelke et al., 1988) and supports the conclusion that the Em is dominated by a proton conductance. 3. The sodium-proton exchanger is present in primitive red cells but quiescent under physiological conditions. 4. The results indicate that the bicarbonate-chloride exchange via Band 3 protein is impaired.

Ionic regulation of the plasma membrane potential of rainbow trout (Salmo gairdneri) spermatozoa: role in the initiation of sperm motility

The ionic dependence of the trout sperm plasma membrane potential was analysed by measuring the accumulation of the lipophilic ions 3H-tetraphenylphosphonium (TPP) and 14C-thiocyanate (SCN) following dilution in artificial media isotonic to the seminal fluid. Our data showed that the trout sperm plasma membrane has a mixed conductance: the plasma membrane potential is sensitive upon the transmembrane gradients of K+, Na+, and H+. This potential is negative (less than -40 mV) in a 125 mM choline chloride media (ChM) at pH 8.5. Replacement of choline by sodium has a small depolarizing effect. The membrane potential is about -15 mV in a 125 mM potassium chloride and falls near zero mV only if valinomycin is added. In ChM changing the external pH (pHe) greatly affects the membrane potential: its value rises from less than -40 mV at pHe 9.0 to -17 mV at pHe 5.0. This pH effect is observed also in presence of sodium or potassium. A decrease in the transmembrane proton gradient produced by increasing internal pH without changing pHe induces also a depolarisation of the plasma membrane. In the different media in which trout sperm remain immotile after dilution (media with [K+] greater than 20-40 mM or a pH less than 7.5) the plasma membrane is more depolarized than in media allowing motility, suggesting a relationship between the state of membrane polarization and the intracellular effectors of the axonemal movement.