ENERGY-DEPENDENT MN2+ AND CA2+ UPTAKE BY EMBRYONIC CHICK CHORIOALLANTOIC MEMBRANE

The chick chorioallantoic membrane is an epithelial tissue which actively transports amounts of Ca2+ during embryonic development. Mn2+ uptake by the tissue was studied and compared to Ca2+ uptake in parallel experiments to determine if Mn2+ could be used as a paramagnetic analog for Ca2+ so that electron paramagnetic resonance could be used to gain more information about the Ca2+ transport system. Mn2+ uptake was reduced significantly under conditions that reduced Ca2+ uptake; 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 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+. Significant amounts of Mn2+ were apparently accumulated by the active Ca2+ transport mechanism. Mn2+ could be a useful paramagnetic probe of divalent cation transport in this tissue.