TRANSEPITHELIAL CALCIUM-TRANSPORT IN THE CHICK CHORIOALLANTOIC MEMBRANE .1. ISOLATION AND CHARACTERIZATION OF CHORIONIC ECTODERM CELLS

The chicken eggshell supplies approximately 80% of the calcium found i n the hatchling chick. The mobilization of eggshell calcium into the d eveloping embryo involves the transepithelial transport of large amoun ts of calcium in a development-specific manner. The cells responsible for the transport of eggshell calcium into the embryonic circulation a re the ectodermal cells of the chorioallantoic membrane. In this repor t, we present a method for the isolation and culture of chorioallantoi c 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 (elevate d Ca2+-activated ATPase). Functional assessment of in vitro cellular c alcium uptake by Ca-45(2+) tracer kinetics indicates the persistence o f a temperature-sensitive, rapid-influx pathway similar to that observ ed in vivo. The preparations of primary ectodermal cells present An in vitro system applicable to the experimental analysis of calcium metab olism and transport by the chick chorioallantoic membrane.