Exocytotic competence and intergranular fusion in cord blood-derived
eosinophils during differentiation
S Scepek and M Lindau
Abt. Molekulare Zellforschung, Max-Planck-Institut f. medizinische
Forschung, Heidelberg, Germany.
We studied degranulation of single cord blood-derived mononuclear cells
differentiating to eosinophils in cultures containing recombinant human
interleukin-5 (rhIL-5) and rhIL-3 by whole-cell patch-clamp capacitance
measurements. As in mature cells, degranulation can be stimulated by
intracellular application of guanosine-5'-O-(3-thiotriphosphate) (GTP)
gamma S after 10 days in culture, simultaneously with the first
morphological appearance of granules. These results demonstrate that the
fusion machineries for exocytotic fusion are present and functional as soon
as the granules are formed, presumably at the myeloblast stage. In the
third week, the total amount of granules exocytosed upon stimulation is
similar to that in mature eosinophils from peripheral blood. The
capacitance step size distributions in promyelocytes and myelocytes confirm
that mature large specific granules are formed by homotypic fusion of unit
granules with similar size. Homotypic fusion is facilitated during early
stages of differentiation associated with granulogenesis. Between day 10
and day 35 in culture the plasma membrane area of resting cells decreases
from approximately 700 microns2 to approximately 400 microns2, approaching
the value of mature cells from peripheral blood. The most prominent
decrease occurs between day 25 and day 35 and is accompanied by the
appearance of an exocytotic component due to small vesicles. This suggests
that a class of small secretory vesicles is formed by endocytosis during a
late phase in maturation.
Volume 89,
Issue 2,
pp. 510-517,
01/15/1997
Copyright © 1997 by The American Society of Hematology
