The major goal of this project is to better understand the responses of individual mammalian cells to extracellular signals. We have previously described modulation of hormone/neurotransmitter receptors on cultured human cells by manipulation of medium components and induction of receptor synthesis and expression by short-chain fatty acids. During this reporting period we have shown that induction of receptor synthesis does not correlate with DNA hypomethylation. We have also described a novel amine transport system with a previously undescribed specificity in several cultured cell lines, including C-6 rat astrocytoma cells; beta-adrenergic antagonists, but not agonists, are taken up at a site clearly distinguishable from the beta-adrenergic receptor. We have also found this amine transport system in a rat pituitary cell line which does not have beta-adrenergic receptors. Amine transport depends on the maintenance of an electrochemical proton gradient across the plasma membrane, which in turn depends on the activity of a MgATPase which appears to reside in the plasma membrane.