RECEPTORS FOR VASOACTIVE-INTESTINAL-PEPTIDE ON MURINE LYMPHOCYTES TURN OVER RAPIDLY

The interaction of the neuropeptide vasoactive intestinal peptide (VIP) with its receptors on murine mesenteric lymph node lymphocytes (MLN) has been re-examined in detail. Intact MLN actively internalize surface bound VIP. The rate constants associated with the insertion of receptors at the MLN surface, the internalization of VIP occupied and unoccupied receptors and the elimination of the peptide were determined. At 37-degree-C, MLN insert approximately 140 VIP receptors cell-1 min-1 at their surface, and the rate of internalization of occupied receptors (0.23 min-1) was much greater than that of the unoccupied receptors (0.02 min-1). Exposure of MLN to non-saturating concentrations of VIP markedly altered the expression of VIP receptors at the lymphocyte surface. The rapid turnover of VIP receptors combined with the differential clearance of occupied and unoccupied receptors from the cell surface provides a mechanism by which homologous regulation of VIP receptor expression can occur on these lymphocytes.