Journal of Experimental Medicine, Vol 143, 937-952, Copyright © 1976 by Rockefeller University Press
Activation and desensitization of platelets by platelet-activating factor (PAF) derived from IgE-sensitized basophils. I. Characteristics of the secretory response
PM Henson
The secretion of vasoactive amines from rabbit platelets induced by the
platelet-activating factor (PAF) derived from IgE-sensitized rabbit
basophils, was examined. The secretion required calcium has previously been
shown to be noncytotoxic and was optimal in both rate and extent at 37
degrees C and pH 7.2. Different temperature-sensitive steps were rate
limiting for secretion above or below 20 degrees C. The rate of secretion
was dependent upon the concentration of PAF and also of platelets. Maximal
rates were observed with relatively low concentrations of platelets (2.5 X
10(8)/ml), sharply contrasting with other platelet stimuli such as C3 or
thrombin. The extent of secretion was dependent upon PAF concentration
until a maximum of 50 or 60% of the serotonin was released and then
declined with increasing amounts of PAF. This was interpreted to result
from the platelets becoming desensitized to the PAF, a process that shuts
off the secretion. Such a desensitization was demonstrated and was shown to
be stimulus specific, i.e., other stimuli could still induce secretion from
PAF-desensitized platelets. PAF extracted with ethanol from the albumin to
which it is usually bound during preparation, exhibited similar
characteristics, except that secretion of up to 90% of the serotonin was
induced. The extracted PAF thus seemed less able to induce the
desensitization. Its use did provide important evidence that populations of
rabbit platelets are relatively homogenous in their ability to respond to
PAF.
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