BETA-ENDORPHIN ENHANCES CONCANAVALIN-A-STIMULATED CALCIUM MOBILIZATION BY MURINE SPLENIC T-CELLS

Intracellular calcium mobilization is an important early event involve d in T cell activation. The endogenous opioid peptide beta-endorphin i s known to modulate immune functions that depend on T cell activation, therefore its effect on intracellular calcium mobilization was invest igated. The intracellular calcium concentration ([Ca2+]i) of T cell-en riched splenocytes was measured by flow cytofluorometric analysis usin g the calcium-sensitive dye, Fluo-3. By gating on the T cell marker, T hy-1, a 95%-pure population of T cells was identified for study. Cells preincubated with beta-endorphin showed significantly enhanced [Ca2+] i responses to the mitogen, Concanavalin A (Con A). This was detectabl e with concentrations of beta-endorphin as low as 10(-13) M; maximal e nhancement required 10(-10) to 10(-9) M doses. The efficacy of beta-en dorphin was dependent on the duration of pretreatment. beta-Endorphin amplified the Con A-induced increase in [Ca2+]i by reducing the lag ti me for the response to Con A and by increasing the mean [Ca2+]i of the cells. N-Ac-beta-endorphin, which shows minimal potency at neuronal o piate receptors, was unable to substitute for beta-endorphin. Naltrind ole, a highly selective delta opiate receptor antagonist, inhibited th e action of beta-endorphin, whereas a selective mu opiate receptor ant agonist was ineffective. Although less potent than beta-endorphin, the delta opiate receptor agonist D-Ala(2)-D-Leu(5)-enkephalin also signi ficantly enhanced [Ca2+]i responses. In summary, concentrations of bet a-endorphin, within the physiological range found in the systemic circ ulation, modulate the increase in T cell [Ca2+]i induced by Con A. Bot h the efficacy of D-Ala(2)-D-Leu(5)-enkephalin alone and the antagonis m of beta-endorphin by naltrindole suggest that a delta-type opiate re ceptor may mediate these effects.