Secretin Receptors on Neuroblastoma Cell Membranes: Characterization of 125I‐Labeled Secretin Binding and Association with Adenylate Cyclase

Abstract

Secretin, a gut-brain peptide, elicited cyclic AMP production in a clone of neuroblastoma cells derived from the C1300 mouse tumor. Adenylate cyclase (EC 4.6.1.1) in plasma membranes from these cells was stimulated by secretin > vasoactive intestinal peptide > peptide histidine isoleucine amide, but not by the related peptides glucagon, gastric inhibitory polypeptide, or human growth hormone releasing factor. Hill coefficients for stimulation approximated one and the response to submaximal peptide concentrations was additive, as expected for hormones competing for a single receptor associated with the enzyme. Binding of ¹²⁵I-labeled secretin to the neuroblastoma plasma membranes was saturable, time-dependent, and reversible. The K_D determined from kinetic and equilibrium binding studies approximated 1 nM. The binding site displayed marked ligand specificity that paralleled that for stimulation of adenylate cyclase. The secretin receptor was regulated by guanine nucleotides, with guanosine 5′-(β,γ-imino)-triphosphate being the most potent to accelerate the rate of dissociation of bound secretin. These findings demonstrate the functional association of the secretin receptor with adenylate cyclase in neuronally derived cells.