Calcium-stimulated respiration and active calcium transport in the isolated chick chorioallantoic membrane

The chick chorioallantoic membrane: a model of molecular, structural, and functional adaptation to transepithelial ion transport and barrier function during embryonic development

The chick chorioallantoic membrane is a very simple extraembryonic membrane which serves multiple functions during embryo development; it is the site of exchange of respiratory gases, calcium transport from the eggshell, acid-base homeostasis in the embryo, and ion and H(2)O reabsorption from the allantoic fluid. All these functions are accomplished by its epithelia, the chorionic and the allantoic epithelium, by differentiation of a wide range of structural and molecular peculiarities which make them highly specialized, ion transporting epithelia. Studying the different aspects of such a developmental strategy emphasizes the functional potential of the epithelium and offers an excellent model system to gain insights into questions partly still unresolved.

Expression of calbindin-D28K by yolk sac and chorioallantoic membranes of the corn snake,Elaphe guttata

The yolk splanchnopleure and chorioallantoic membrane of oviparous reptiles transport calcium from the yolk and eggshell to the developing embryo. Among oviparous amniotes, the mechanism of calcium mobilization to embryos has been studied only in domestic fowl, in which the mechanism of calcium transport of the yolk splanchnopleure differs from the chorioallantoic membrane. Transport of calcium is facilitated by calbindin-D(28K) in endodermal cells of the yolk splanchnopleure of chickens but the chorioallantoic membrane does not express calbindin-D(28K). We used immunoblotting to assay for calbindin-D(28K) expression in yolk splanchnopleure and chorioallantoic membrane of the corn snake, Elaphe guttata, to test the hypothesis that the mechanism of calcium transport by extraembryonic membranes of snakes is similar to birds. High calbindin-D(28K) expression was detected in samples of yolk splanchnopleure and chorioallantoic membrane during late embryonic stages. We conclude that calbindin-D(28K) is expressed in these extraembryonic membranes to facilitate transport of calcium and that the mechanism of calcium transport of the chorioallantoic membrane of the corn snake differs from that of the chicken. Further, we conclude that calbindin-D(28K) expression is developmentally regulated and increases during later embryonic stages in the corn snake.

Sources and timing of calcium mobilization during embryonic development of the corn snake, Pantherophis guttatus

Embryos of oviparous Reptilia (=turtles, lepidosaurs, crocodilians and birds) extract calcium for growth and development from reserves in the yolk and eggshell. Yolk provides most of the calcium to embryos of lizards and snakes. In contrast, the eggshell supplies most of the calcium for embryonic development of turtles, crocodilians and birds. The yolk sac and chorioallantoic membrane of birds recover and transport calcium from the yolk and eggshell and homologous membranes of squamates (lizards and snakes) probably transport calcium from these two sources as well. We studied calcium mobilization by embryos of the snake Pantherophis guttatus during the interval of greatest embryonic growth and found that the pattern of calcium transfer was similar to other snakes. Calcium recovery from the yolk is relatively low until the penultimate embryonic stage. Calcium removal from the eggshell begins during the same embryonic stage and total eggshell calcium drops in each of the final 2 weeks prior to hatching. The eggshell supplies 28% of the calcium of hatchlings. The timing of calcium transport from the yolk and eggshell is coincident with the timing of growth of the yolk sac and chorioallantoic membrane and expression of the calcium binding protein, calbindin-D28K, in these tissues as reported in previous studies. In the context of earlier work, our findings suggest that the timing and mechanism of calcium transport from the yolk sac of P. guttatus is similar to birds, but that both the timing and mechanism of calcium transport by the chorioallantoic membrane differs. Based on the coincident timing of eggshell calcium loss and embryonic calcium accumulation, we also conclude that recovery of eggshell calcium in P. guttatus is regulated by the embryo.

Calcium uptake by chorioallantoic membrane: effects of vitamins D and K

The chorioallantoic membrane (CAM) of birds is an epithelial tissue that actively transports large amounts of Ca during embryonic development. In this study the effect of vitamins D and K on Ca uptake by the CAM was studied. Four dietary treatments were used to produce eggs that are the following: deficient in vitamins D and K (-D/-K), sufficient in both (+D/+K), or deficient in one and sufficient in the other (-D/+K or +D/-K). Vitamin D-deficient (-D) Japanese quail embryos (from hens fed 1,25-dihydroxyvitamin D3) do not hatch because of severe Ca deficiency resulting from their inability to obtain Ca from shell, whereas vitamin K deficiency results in only 14% reduction in hatchability. The results demonstrate that Ca uptake by CAM is vitamin D dependent and only slightly vitamin K dependent. Ca-binding activity of CAM extracts was unchanged by vitamin K deficiency, and only a small increase was provided by vitamin D treatment. Vitamin D stimulated both Ca entry and exist from the chorion cells as indicated by the increased accumulated 45Ca in +D embryos. We conclude that vitamin D is essential for the utilization of eggshell Ca by the developing embryo and hence its survival, suggesting that Ca transport across the CAM is largely a vitamin D-dependent process.

Transepithelial calcium transport in the chick chorioallantoic membrane. I. Isolation and characterization of chorionic ectoderm cells

The chicken eggshell supplies approximately 80% of the calcium found in the hatchling chick. The mobilization of eggshell calcium into the developing embryo involves the transepithelial transport of large amounts of calcium in a development-specific manner. The cells responsible for the transport of eggshell calcium into the embryonic circulation are the ectodermal cells of the chorioallantoic membrane. In this report, we present a method for the isolation and culture of chorioallantoic membrane ectodermal cells, which are amenable to direct experimental manipulation. Cell preparations are characterized with respect to the expression of an ectoderm-specific cell surface marker (transcalcin, a calcium-binding protein), and a specific enzymatic activity (elevated Ca(2+)-activated ATPase). Functional assessment of in vitro cellular calcium uptake by 45Ca2+ tracer kinetics indicates the persistence of a temperature-sensitive, rapid-influx pathway similar to that observed in vivo. The preparations of primary ectodermal cells present an in vitro system applicable to the experimental analysis of calcium metabolism and transport by the chick chorioallantoic membrane.

Transepithelial calcium transport in the chick chorioallantoic membrane. II. Compartmentalization of calcium during uptake

Calcium transport from the eggshell to the developing chick embryo is carried out by the ectoderm cells of the chick chorioallantoic membrane. Primary cells isolated from chick chorioallantoic membrane ectoderm were used to analyze the subcellular distribution of 45Ca2+ accumulated from the extracellular medium. We present evidence suggesting that calcium may be sequestered into endosome-like vesicles during the initial phase of uptake. A combination of techniques were utilized to monitor calcium fluxes and calcium compartmentalization in the cultured chorioallantoic membrane cells: (1) fura-2 fluorescence was used to indicate cytosolic free calcium concentrations, (2) 45Ca2+ tracer was used to follow calcium accumulation in all cellular compartments, and (3) digitonin was used to differentially permeabilize subcellular membranes in order to localize 45Ca2+ by following tracer release profiles. Differences between cytosolic calcium flux and whole cell calcium accumulation suggested that the pathway of calcium uptake from the medium involves sequestration into an internal compartment separate from the cytosol. Kinetic analysis of the digitonin-mediated release of specific subcellular markers (lactate dehydrogenase, NAD-dependent isocitrate dehydrogenase, [3H]inulin, and [3H]-2-deoxyglucose) and preloaded 45Ca2+ indicated that calcium was localized in a compartment similar to endosomal vesicles. Our results are consistent with a transcytotic mechanism for chorioallantoic membrane calcium transport.

Oxygen consumption of the chick embryo's respiratory organ, the chorioallantoic membrane

A new technique based on stopping the chick embryo's blood circulation in the intact egg was used to measure in situ the chorioallantoic (CA) oxygen consumption, MCAO2, from incubation day 12 to 20. Total egg MO2, MTOTO2, and wet and dry masses of embryo and CA were also measured daily. Embryo MO2, MEMBO2, was calculated. Mean MCAO2 decreased from 71 mumol X h-1 (17% of MTOTO2, 24% of MEMBO2) at 12 days to 62 mumol X h-1 (5% of MTOTO2) at 20 days. Dry mass of CA did not change significantly. Water remained at a high level in CA (88-94%), but embryo water decreased from 93% to 82% between days 12 and 20. The fairly high level of MCAO2, more marked at young stages, calls for corrections in respiratory and circulatory embryonic variables derived from MTOTO2, such as CA blood flow, CA diffusive capacity for O2, and CA arterio-venous shunt. Mass specific values and intra-specific allometric relations in bird embryos should be recalculated on the basis of MEMBO2 instead of MTOTO2.

An electron paramagnetic resonance study of Mn2+ uptake by the chick chorioallantoic membrane

Mn2+ uptake in the chick chorioallantoic membrane, an embryonic epithelial tissue which transports Ca2+ in vivo was studied using electron paramagnetic resonance (EPR). Mn2+ was used as a paramagnetic analog for Ca2+, since there is evidence that Mn2+ is accumulated by the Ca2+ transport mechanism. After 1.5 h of uptake the EPR spectrum of the Mn2+ in the membrane indicated that 89% of the Mn2+ was in a spin-exchange form, indicating close packing of Mn2+. The Mn2+ spacing was estimated from the line width to be about 4.7 A. The remaining Mn2+ was very likely Mn2+ hexahydrate. At pH 7.4 the spin-exchange spectrum tended to broaden when uptake was inhibited, while at pH 5.0 the spin-exchange spectrum was completely abolished in the presence of inhibitors. The EPR spectrum of Mn2+ in the chorioallantoic membrane had a broader line width than that of Mn2+ in isolated mitochondria, suggesting that in this tissue mitochondria are not directly involved in divalent cation transport. These EPR studies support the concept that divalent cations are sequestered in high concentrations from the rest of the cell contents during transcellular active transport.

Energy-dependent Mn2+ and Ca2+ uptake by the embryonic chick chorioallantoic membrane

The chick chorioallantoic membrane is an epithelial tissue which actively transports large amounts of Ca2+ during embryonic development. In this paper Mn2+ uptake by the tissue was studied and compared to Ca2+ uptake in parallel experiments. The purpose of these experiments was to determine if Mn2+ could be used to gain more information about the Ca2+ transport system. It was found that Mn2+ uptake was reduced significantly under conditions that reduced Ca2+ uptake and that Mn2+, like Ca2+, was taken up preferentially by the ectodermal side of the tissue. Mn2+ uptake showed saturation kinetics with a Km of 0.33 MM. Mn2+ uptake was also competitively inhibited by Ca2+, and Ca2+ uptake inhibited by Mn2+. Electron microprobe studies showed that Mn2+ was localized in the ectoderm of the tissue in the same way as Ca2+. It was concluded from these studies that significant amounts of Mn2+ were accumulated by the active Ca2+ transport mechanism and that Mn2+ could be useful paramagnetic probe of divalent cation transport in this tissue.