Interaction of vasoactive intestinal peptide (VIP) with rat lymphoid cells

Abstract

Receptors for vasoactive intestinal peptide (VIP) have been characterized in rat lymphoid cells. The interaction of [ 125I] VIP with blood mononuclear cells was rapid, reversible, specific and saturable. At apparent equilibrium, the binding of [ 125I] VIP was competitively inhibited by native VIP in the 0.01–100 nM range concentration. The binding data were compatible with the existence of two classes of receptors: a high-affinity class with a Kd=0.050±0.009 nM and a low binding capacity ( 2.60±0.28 fmol/10 6 cells), and a low-affinity class with a Kd=142±80 nM and a high binding capacity ( 1966±330 fmol/10 6 cells). Secretin, glucagon, insulin and somatostatin did not show any effect at a concentration as high as 100 nM. With spleen lymphoid cells, stoichiometric studies were performed. The binding data were compatible with the existence of two classes of receptors: a high-affinity class with a Kd=0.100±0.033 nM and a low binding capacity ( 4.60±1.07 fmol/10 6 cells), and low-affinity class with a Kd=255±110 nM and high binding capacity ( 2915±1160 fmol/10 6 cells). With thymocytes, no binding was obtained under different conditions.