Sodium-dependent short-circuit current across the yolk sac membrane during embryonic development in normal and shell-less cultured chicks

Summary The transepithelial electrical characteristics of the isolated yolk sac membrane of normal in ovo or shell-less cultured chick embryos were investigated. In normal chicks the potential difference (blood side positive relative to yolk side) and short-circuit current of the membrane increased during development. Ouabain (10^-4 M) on the blood side (basolateral side, serosal side) significantly decreased potential difference and short-circuit current but was without effect on the yolk side (brush border side, mucosal side). Substitution of choline for Na⁺ in the bathing solutions abolished the potential difference and the short-circuit current; when Na⁺ replaced choline this effect was reversed. Amiloride added to both sides of the yolk sac membrane had no effect on potential difference or short-circuit current. Injection of aldosterone (50 g) and T₃ (10 M) into yolk did not induce amiloride sensitivity. The short-circuit current was not altered by addition of either glucose or alanine to the bath. The short-circuit current of the yolk sac membrane of shell-less cultured embryos was significantly lower than that of normal controls. Addition of Ca²⁺ to the serosal bathing medium did not reverse the foregoing condition, but decreased the short-circuit current. It is concluded that the yolk sac short-circuit current is Na⁺ dependent and increases with developmental age in the chick embryo.Abbreviations Hepes N-2-hydroxyethylpiperazine-N-2-ethaneoulphonic acid - PD potential difference - R resistance - SCC short-circuit current - TRIS tris-hydroxymethyl aminomethane - T₃ 3,3-5-triiodo-l-thyronine