EXPRESSION OF NALOXONE-RESISTANT BETA-ENDORPHIN BINDING-SITES ON A20 CELLS - EFFECTS OF CONCANAVALIN-A AND DEXAMETHASONE

beta-Endorphin affects mononuclear cell proliferation, cytokine produc tion and calcium uptake in a naloxone-resistant manner. The presence o f naloxone-insensitive binding sites for beta-endorphin have been demo nstrated on murine EL4-thymoma cells, transformed human mononuclear ce lls and normal murine splenocytes. Since murine splenic B cells have b een shown to express naloxone-resistant receptors for beta-endorphin i n response to the mitogen, concanavalin A (Con A), the A20 B-cell lymp homa line was used to further study regulation of this site by Con A a nd dexamethasone. Analyses showed two sites: a high-affinity site, K-d 1 = (8.7 +/- 2.3) x 10(-11) M and binding capacity (B-max1) of (2.6 +/ - 2.0) x 10(3) receptors/cell; and a low-affinity site, K-d2 = (2.2 +/ - 0.8) x 10(-8) M with B-max2 of (1.5 +/- 0.8) x 10(5) receptors/cell. Competition studies showed that N-acetyl-beta-endorphin was approx. 5 -fold and beta-endorphin(6-31) 10-fold less potent than beta-endorphin (1-31). Neither beta-endorphin(1-27) nor naloxone, morphine or other o pioid receptor agonists displaced [I-125]beta-endorphin. Con A (20 mu g/ml) significantly increased the B-max (3.5-fold; expressed per cell) and resulted in a loss of the higher-affinity site. However, the incr eased B-max occurred in proportion to the Con-A-induced increase in pr otein/cell. Dexamethasone (Dex) also increased B-max primarily by incr easing (2-3-fold) the number of lower affinity sites. In contrast to C on A, two binding sites persisted after treatment with Dex, which exer ted a minimal effect on protein/cell. Therefore, binding/cell and bind ing/protein/cell were both significantly enhanced by Dex. The combined effects of Dex and Con A on binding failed to show additivity or syne rgy. When binding was analyzed per protein/cell, the effect of Con A a ppeared to dominate; the Dex-enhanced binding/protein/cell was no long er evident in the presence of Dex plus Con A. Thus, Dex and Con A may enhance binding by independent mechanisms.