On the cation exchanger properties of rat mast cell granules and their storage of histamine.

Mast cell granules free of a surrounding membrane were isolated from water-lysed rat peritoneal and thoracic mast cells by differential centrifugation. The granules were depleted of their histamine by suspension in 10 mM sodium phosphate buffer and the sodium-charged granules then converted into the "hydrogen form" by repeated washing in slightly acid deionized water. The cation exchanger properties of the mast cell granules were investigated by testing the applicability of the Rothmund-Kornfeld equation for cation exchangers to the binding of Na+ and Hi+ ions to granule sites. The results lend further support to the view that the mast cell granule acts as a cation exchanger with the exchanger function localized to protein carboxyls in the protein-heparin complex of the granule matrix.