CALCIUM TRANSPORT BY THE CHICK CHORIOALLANTOIS IN VIVO

Abstract

A technique is described for attaching a perspex annulus to the chorioallantoic membrane of the chick embryo. Radioactive saline is placed on this membrane and the uptake measured in vivo. The method gives calcium influx values of 85-4 n mole/cm2/hr for 12-day and 115-9 n mole/cm2/hr for 15-day embryos. Efflux Leeson, 1963;Stewart and Terepka, 1969]. From then on relatively few changes occur in the morphology of the cells until the 18th day when the membrane begins to dry up prior to the hatching of the chick on day 21.The chorioallantoic membrane is involved in a remarkable number of ionic activities. On the allantoic side the pH of the embryonic urine changes from 7-5 to 5-5 on the 14th day of incubation [Walker, 1943;Abramovici, 1967]. This is followed by the movement of sodium and chloride ions and the rapid resorption of this fluid back into the embryo [Terepka, Stewart and Merkel, 1969]. The chorionic cells are also involved in the transport of sodium and chloride ions inwards [Moriarty and Hogben, 1970] and in addition they probably secrete acids or protons onto the eggshell [Crooks and Simkiss, 1974]. Perhaps the most remarkable property of the chorionic cells, however, is their ability to transport calcium ions from the eggshell into the circulation of the embryo. This phenomenon has been studied in vitro and shown to be an active process requiring oxidative phosphorylation [Garrison and Terepka, 1972a and b]. Unfortunately the in vitro preparation is characterized by a rapid fall in its transepithelial potential difference, in its short circuit currents, and in its membrane resistance. This suggests 'tissue death' [Moriarty, 1973] and since this preparation also transports less calcium than normally occurs in ovo an attempt was made to develop an in vivo preparation which would enable the calcium transporting properties of this tissue to be studied under more physiological conditions.

Functional involvement of carbonic anhydrase in calcium transport of the chick chorioallantoic membrane

“…Initial kinetic studies showed that a linear rate of Ca2+ uptake in vivo by the chorioallantoic membrane was maintained for up to 20min of incubation. These observations confirm the earlier studies by Simkiss (1975) andCrooks et al (1976) and demonstrate that these measurements are valid representations of the rates of Ca2+ transport in vivo by the chorioallantoic membrane. With this technique, the age profile of the Ca2+-transport activity of the chorioallantoic membrane in vivo was determined and is shown in Fig.…”

“…Their findings, together with the observable progressive increase in skeletal calcification of the embryo during development (Romanoff, 1967), strongly suggest that, in vivo, the Ca2+-transport function of the chorioallantoic membrane should also increase in capacity as the embryo matures. This supposition was tested here by means of a Ca2+_ transport system in vivo (Crooks & Simkiss, 1975;Crooks et al, 1976). Initial kinetic studies showed that a linear rate of Ca2+ uptake in vivo by the chorioallantoic membrane was maintained for up to 20min of incubation.…”

“…During embryonic skeletal calcification, the chorioallantoic membrane is responsible for mobilizing over 100mg of calcium from the egg shell into the embryonic circulation (Johnston & Comar, 1955;Romanoff, 1967). The Ca2+-transport function of the chorioallantoic membrane is highly developmentally regulated, beginning after the days 12-13 of incubation of the chick embryo, and continuing to increase steadily until hatching (Terepka et al, 1969;Crooks & Simkiss, 1975). Calcium transport is carried out by the ectodermal cells and is highly specific for Ca2+ ions (Terepka et al, 1969;Garrison & Terepka, 1972;Terepka et al, 1971).…”

Routes of Calcium Movement Across the Chick Chorioallantois

“…In the case of the chick chorioallantois a third theory suggests that calcium is moved across the chorion in pinocytotic vesicles which discharge close to the capillaries of this membrane [Coleman and Terepka, 1972]. It is not clear, however, whether these different theories are all intended to be part of one basic transporting system or whether different tissues perform this function in different ways [Simkiss, 1975].A technique has recently been described for studying, quantitatively, calcium fluxes across the chick chorioallantoic membrane in vivo [Crooks and Simkiss, 1975]. It was decided, therefore, to use this method to collect information on this tissue which would be relevant to the various different theories of calcium translocation.…”

“…A technique has recently been described for studying, quantitatively, calcium fluxes across the chick chorioallantoic membrane in vivo [Crooks and Simkiss, 1975]. It was decided, therefore, to use this method to collect information on this tissue which would be relevant to the various different theories of calcium translocation.…”