Lipocortin I (p35) is abundant in a restricted number of differentiated cell types in adult organs.

Lipocortin-I (p35) is a unique calcium- and phospholipid-binding protein of the lipocortin/calpactin family. Although several possibilities have been suggested, functions for the individual proteins of this family are not yet known with certainty. As an initial step in the identification of the biological function(s) of p35, we have used immunohistochemical methods to define precisely many of the cellular phenotypes that contain p35 in vivo. In all organs where p35 is found, we have observed a striking distribution of p35-positive cells. Typically it is highly enriched in a limited range of differentiated cell types while apparently totally absent from most others. Our identification of specific p35-positive cell types in vivo will now set limitations on likely possibilities for functions of this protein and thereby permit a more logical approach to the determination of its true function.