Removal of Extracellular Mg²⁺ Suppresses Sulfation of Glycoconjugates Secreted from Rabbit Trachea in Culture

Abstract

The influences of extracellular Ca²⁺ and Mg²⁺ concentrations on the basal secretion of glycoconjugates from rabbit trachea in organ culture were examined. Over 80% of the ³⁵S-labeled and [³H]glucosamine-labeled glycoconjugates secreted by the trachea were digested upon incubation with chondroitinase ABC. The basal secretion did not occur in the medium at 4°C, indicating an energy-dependent process. The basal secretion at 37°C of ³⁵S-labeled glycoconjugates was prominently suppressed in Mg²⁺-free Tyrode solution but not in Ca²⁺-free Tyrode solution containing ethyleneglycol bis(2-aminoethylether)tetraacetic acid (EGTA). In contrast, the basal secretion of [³H]glucosamine-labeled glycoconjugates was not affected by the Mg²⁺ concentration in the medium. The results suggest that extracellular Mg²⁺ largely contributes to sulfation of glycoconjugates basally secreted from rabbit trachea.