BOMBESIN TREATMENT ENHANCES VASOPRESSIN RECEPTORS IN SWISS 3T3 CELLS

Cells possess receptors for multiple different peptides that regulate a wide spectrum of biological processes. Although examples of homologous and heterologous downregulation have been reported, relatively little is known about the interaction between different peptides in modulating cellular activities. Here we demonstrate that pretreatment of Swiss 3T3 fibroblasts with 10 nM bombesin for 48 h enhanced the Ca-45(2+) efflux acutely stimulated by vasopressin. The effect was not reciprocal, since preincubation with vasopressin did not affect the bombesin-stimulated Ca2+ efflux. Measurement of displaceable [H-3]vasopressin binding demonstrated that bombesin pretreatment increases the hormonal binding by 3.8 +/- 0.2-fold (SE; n = 14) measured at 37-degrees-C or at 4-degrees-C. Scatchard analysis at 4-degrees-C indicated that the increased binding reflects an increase in the number of vasopressin receptors without any significant effect on the apparent affinity of binding. Furthermore, addition of cycloheximide completely prevented the increase in [H-3]vasopressin binding induced by bombesin. We conclude that long-term bombesin pretreatment induces heterologous enhancement of vasopressin responsiveness by increasing the number of membrane receptors.