BETA-ENDORPHIN MODULATES CALCIUM-CHANNEL ACTIVITY IN HUMAN NEUTROPHILS

10(-6) M n-formyl-methionyl-leucyl-phenylalanine (FMLP) stimulated Ca2 + flux in human neutrophils is characterized by a profile composed of two peaks of different amplitude and breadth. beta-Endorphin inhibited the magnitude and modulated the kinetics of the second peak in a mann er which was dose-dependent and could reflect either negative cooperat ivity or heterogeneity of binding sites. The second peak arises from c alcium channel activity since in the presence of nifedipine or EGTA it was not evident while the first peak was reduced about 24%. Similarly , at 15 degrees C, where we were unable to detect any channel activity , the first peak was diminished by 35% and beta-endorphin had no detec table effect on this peak. These results led us to conclude that the f irst peak is chiefly composed of Ca2+ recruited from cytosolic stores which are relatively insensitive to the above treatments and a smaller fraction of calcium originating in calcium channel activity. Hence, w e reason that beta-endorphin modulates only the calcium ion flux arisi ng from calcium channel function.