| Abstract: | As a first step towards the identification and purification of the molecule(s) that are involved in cell contact-mediated tyrosine hydroxylase (TH) induction in cultures of bovine adrenal chromaffin cells, we have prepared plasma membranes (PM) from bovine adrenal medulla and tested their ability to mimick cell contact-mediated TH induction in low density chromaffin cultures. PM indeed induced TH in a manner similar to that observed in high density cultures. The maximal TH induction reached by PM corresponded to 69% of that of high density cultures, and half-maximal TH induction was obtained with 12 micrograms of PM per ml of medium. The induction of TH by PM was blocked by alpha-amanitin as observed in high density cultures. Since acetylcholinesterase was neither induced in high density nor in PM-treated low density cultures, an induction of TH as a result of a general increase in protein synthesis was excluded. The cell contact molecule(s) appear to be intrinsic membrane proteins. They were not removed by high or low salt extraction, but solubilized by 50 mM octylglucoside. They were resistant to 0.1% trypsin and heat denaturation but inactivated by 0.01% chymotrypsin. PM isolated from the adrenal cortex, kidney, and liver also induced TH in low density chromaffin cell cultures, although to a smaller extent than PM of the adrenal medulla. In contrast, muscle and erythrocyte PM were inactive. This shows that the cell contact molecule(s) are not restricted to the adrenal medulla, but are also present in some other but not all tissues. |
