INSERTION AND INTERNALIZATION OF VASOACTIVE-INTESTINAL-PEPTIDE (VIP) RECEPTORS IN MURINE CD4 LYMPHOCYTES-T

The specific binding of vasoactive intestinal peptide (VIP) to murine lymphocytes was investigated. CD4 T cells from mesenteric lymph nodes (MLN) bound more I-125-VIP than did unseparated MLN lymphocytes at 37-degrees-C, but not at 4-degrees-C. The differences between the amount of I-125VIP bound by the CD4 T cells and unseparated MLN lymphocytes at 37-degrees-C depended upon a difference in the amount of the ligand that was internalized by the cells. The rate of insertion of unoccupied VIP receptors from the cytoplasm into the cell membrane (370 receptors/cell/min), the rate constants for internalization of ligand occupied VIP receptors (0.55 min-1) and unoccupied VIP receptors (0.11 min-1), and the rate constant for the elimination of internalized VIP (0.07 min-1) by CD4 T cells were evaluated. These results provide new understanding of the behaviour of VIP receptors on lymphocytes and indicate a mechanism by which CD4 T lymphocytes can homologously regulate their surface expression of VIP receptors in the presence of ambient VIP.