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MO Spycher and UE Nydegger
The differential uptake of tritium-labeled immunoglobulin G (IgG) cross-
linked with bisdiazonium-benzidine (BDB) (3H-BDB-IgG) by washed, pooled
human platelets to sites inaccessible to pronase digestion was tested. Up
to 52% of the 3H-BDB-IgG associated with platelets at 37 degrees C resisted
pronase treatment, whereas only 23% of the cross-linked IgG associated with
platelets at 4 degrees C, or at 37 degrees C but in the presence of
deoxyglucose/antimycin A, remained refractory to pronase. This effect was
not due to platelet agglutination. Pronase resistance reached a maximum
after a 60-minute incubation period at 37 degrees C. With increasing
3H-BDB-IgG input, both the total cross-linked IgG associated with platelets
and the fraction resistant to pronase digestion approached saturation at 4
degrees C, but not at 37 degrees C. The proportion of 3H-BDB-IgG bound to
platelets at 4 degrees C that was resistant to pronase treatment increased
by 13% within five minutes of warming the platelets to 37 degrees C.
Pretreatment of platelets with 10 mmol/L acetylsalicylic acid (or 10
mumol/L prostaglandin E1) prior to the addition of 3H-BDB-IgG led to a 74%
(95%) inhibition of the 3H-BDB-IgG-induced 14C-serotonin release, but to
only a 44% (49%) inhibition of pronase-digestible bound ligand. In
contrast, pretreatment with 10 mumol/L cytochalasin B led to a mere 17%
reduction of 14C-serotonin release, whereas acquisition of resistance to
pronase digestion by the bound 3H-BDB-IgG was inhibited by 90%. Incubation
of platelets at 37 degrees C with 3H-BDB-IgG and removal of unbound
material prior to the addition of prostaglandin E1 or
deoxyglucose/antimycin A had little effect on the susceptibility of
platelet-associated 3H-BDB-IgG to pronase, whereas the addition of
cytochalasin B to 3H-BDB-IgG-treated platelets resulted in greatly
increased susceptibility of the platelet-associated ligand to pronase.
Thus, after binding, 3H-BDB-IgG becomes transferred in an energy- dependent
process to pronase-resistant cellular sites, most likely to the open
canalicular system.
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| Copyright © 1986 by American Society of Hematology Online ISSN: 1528-0020 | |||||||||