Abstract
AbstractSonicated rabbit and rat platelets were subjected to differential centrifugation and the mixed organelle fraction so obtained then separated by ultracentrifugation on a discontinuous sucrose gradient. The distribution curves for 5‐hydroxytryptamine (5‐HT), histamine (studied in rabbit only) and adenosine‐5′‐triphosphate (ATP) were similar. Electron microscopy of the amine‐containing fractions revealed the presence of very dense granules. These fractions contained little or no hexosamine or 35S, two indicators of the presence of sulphomucopoly‐saccharides (SMPS). A second type of granule, a‐granules, was found in fractions corresponding to peaks on the hexosamine and 35S distribution curves. The observation that in rabbit 5‐HT, histamine and ATP are localized to the same subcellular fractions as the very dense granules agrees with the results of earlier workers. An analogous situation appears to exist in rat platelets. The biogenic function of the SMPS‐containing a‐granules remains uncertain. It might be suggested that they, like the mast cell granules, utilize their SMPS‐protein complex for the storage of electrically charged substances.
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