Transepithelial calcium transport in the chick chorioallantoic membrane. I. Isolation and characterization of chorionic ectoderm cells.
Calcium markedly stimulates the respiration of the isolated chick chorioallantoic membrane. This stimulation of oxygen uptake appears to be closely associated with the membrane's active transcellular calcium transport mechanism. In the presence of 1mm Ca++ the rate of uptake increases from 9.3±0.15 to 13.0±0.2 μliters O2/cm2/hr, an increase of about 40%. The calcium-stimulated respiration is specific for the ectodermal layer of cells, the known location of the calcium transport mechanism, and only occurs when the calcium transport mechanism is operative. Sr++ and Mn++ are transported by the tissue at a lower rate than Ca++ and cause a smaller stimulation of oxygen consumption. Mg++ and La3+ have no effect on tissue respiration. In the presence of Ca++, the organic mercurialp-chloromercuribenzene sulfonate (PCMBS) inhibits calcium transport and specifically decreases the oxygen uptake of the ectoderm to a rate identical to that obtained in a calcium-free medium. Stripping the inner shell membrane away from the chorioallantoic membrane mimics these effects. The specificity and locus of action of these two inhibitors suggest that a vital component of the active transcellular calcium transport mechanism resides on or near the outer surface of the plasma membrane of the ectodermal cells and that sulfhydryl groups are important to the normal function of this component.