Do Secretin and Vasoactive Intestinal Peptide Have Independent Receptors on Striatal Neurons and Glial Cells in Primary Cultures?

Abstract

Vasoactive intestinal peptide (VIP) and secretin are two related peptides that activate adenylate cyclase on membranes of striatal neurons and glial cells from embryonic mouse brain grown in primary culture. On the two cell types, the maximal activation that could be induced by secretin was only 40% above basal activity, which represented < 15% of the maximal effect obtainable with VIP. From competition experiments performed on glial cells and the neuroblastoma .times. glioma hybrid, NG-108-15, a cell line known to possess both VIP and secretin sensitive-adenylate cyclase, were demonstrate that secretin does not activate VP receptors. Furthermore, secretin has an apparent high affinity (EC50 10-8 M) for its receptors on striatal neurons and NG 108-15 whereas an apparent low affinity (EC50 7 .times. 10-6 M) was found on strial glial cells. This suggests the existence of either two distinct secretin receptors or a desensitized form.