Effect of permeabilization on [³H]5-HT output from platelets.

(A) Time course of [³H]5-HT output from intact and permeabilized cells in the presence or absence of PMA. [³H]5-HT–labeled platelets were used and were permeabilized for 4 different periods of time with 15 μM of digitonin in K⁺-glutamate buffer. When indicated, PMA (100 nM) was present during the entire incubation period. After incubation, platelets were recovered by centrifugation, and the content of [³H]5-HT was measured in the medium and in the platelets. [³H]5-HT outputs were expressed as a percentage of total content. Values represent the mean ± SEM of at least 8 different preparations. (B) Effect of permeabilization is shown for different periods of time on the responses to a short period of stimulation with PMA. [³H]5-HT–labeled platelets were permeabilized as indicated in A, and they were stimulated for 45 seconds with 100 nM of PMA. Platelets were recovered by stimulation, and [³H]5-HT output was measured. Bars represent the mean ± SEM of 4 different preparations.