DIFFERENTIAL-EFFECTS OF COLCHICINE AND CYTOCHALASINS ON THE SHEDDING OF MURINE B-CELL MEMBRANE IGM AND IGD

Lactoperoxidase (EC 1.11.1.7) catalyzed cell surface radioiodination was employed to monitor the fate of murine B cell membrane (mem) IgM and IgD on radiolabeled cells in short-term culture. Both mem-IgM and mem-IgD were shed from the cell surface with biphasic kinetics. The rapid phase of mem-IgD shedding was somewhat slower (half-time = 12 hr) than that of mem-IgM shedding (half-time = 7-8 hr). The effect of temperature, colchicine, and cytochalasin on the shedding of the two membrane immunoglobulin isotypes was determined. The shedding of mem-IgD was more energy dependent than that of mem-IgM and was sensitive to colchicine but not cytochalasin. Conversely, the shedding of mem-IgM was sensitive to cytochalasin but not colchicine. The results suggest that the mechanisms of shedding of mem-IgM and mem-IgD are qualitatively distinct and may be regulated by microfilaments or microtubules, respectively.