Intramembranous response to cAMP in fetal epidermis.

Prekeratinized fetal epidermis may function as an osmoregulatory organ. This study shows that the structural response of fetal epidermis to cAMP (second messenger of antidiuretic hormones) is very similar to that in well characterized osmoregulatory epithelia. cAMP stimulation of unkeratinized fetal epidermis induces the appearance of "aggregates" of intramembranous particles. These aggregates are present in the apical plasma membrane of the periderm or outermost cell layer of the epidermis. Tubular vesicles that contain the presumptive aggregates fuse with the apical plasma membrane during cAMP stimulation. The same response to cAMP and to antidiuretic hormones has been reported in the osmoregulatory ion- and water-transporting epithelia of amphibian urinary bladder and mammalian collecting ducts. In these systems aggregates have been positively correlated with water transport. Thus, the fetal epidermis may control and regulate its water permeability.