The glucose-6-phosphatase enzyme in developing human trachea and oesophagus

Glucose-6-phosphatase is an endoplasmic reticulum system which is found primarily in liver and kidney. Recently, it has become clear that it is also present in lower amounts in a variety of other tissues. Previous histochemical studies of glucose-6-phosphate hydrolysis in trachea have given equivocal results and only one study on adult oesophagus has shown glucose-6-phosphatase, enzymatic activity but without cellular localization. We have now shown, using microassay techniques, that microsomes isolated from human foetal trachea and oesophagus both contain low levels of specific glucose-6-phosphatase activity (mean = 0.9 and 1.5 nmol min-1 mg-1 microsomal protein, respectively) which are less than 10% of the levels in microsomes of human foetal liver of similar age. In the developing trachea, glucose-6-phosphatase immunoreactivity has been found, using a monospecific antibody to the catalytic subunit of the glucose-6-phosphatase enzyme, to be first present at 10-11 weeks' gestation, and thereafter in foetal life, predominantly present in ciliated cells, with smaller amounts in non-ciliated secretory cells, duct lining cells, and occasional basal cells. The foetal oesophageal epithelium is transiently ciliated from 10 to 11 weeks' gestation, but ciliated cells are gradually replaced by squamous cells from 14 to 16 weeks onwards. Glucose-6-phosphatase immunoreactivity in human foetal oesophagus is predominantly confined to ciliated cells, but non-ciliated luminal cells are also reactive, as are occasional basal cells. Mucus secretory cells in foetal trachea and oesophagus are immunonegative, as is the entire epithelium of both organs in the embryo (up to 56 postovulatory days.