Rat intestinal mucosal mast cells (IMMC) differ from peritoneal mast cells (PMC) in many characteristics. We employed two-dimensional gel electrophoresis (2-D gel) to characterize proteins of these mast cell subtypes, and developed procedures to study protein synthesis. Marked differences were identified in the protein compositions of IMMC and PMC. Most apparent were differences in the constituents of the cytoplasmic granules especially among proteins with a basic pI. Certain basic proteins in both mast cell subtypes bound the serine protease inhibitor 3H-diisopropyl fluorophosphate (DFP), and in immunoblotting experiments with specific antibodies to rat mast cell protease (RMCP) I and II, RMCPI in PMC was identified as a single entity of 26 kDa, pi > 9.0, whereas RMCP II in IMMC appeared as four isoforms of 24 kDa, 8 < pi < 9. In vitro translation of mRNA from PMC and IMMC uncovered that the two mast cell subtypes differ markedly in the spectrum of polypeptides synthesized. These approaches will help uncover the molecular bases of mast cell pleomorphism.
