Amine uptake into intact mast cell granules in vitro

Area of Science:

• Cell Biology
• Pharmacology
• Biochemistry

Background:

• Mast cells are crucial in allergic responses, releasing histamine from granules.
• Understanding amine transport mechanisms in mast cells is key to modulating histamine release.

Purpose of the Study:

• To investigate the transport mechanisms of histamine and serotonin (5-HT) into isolated rat mast cell granules.
• To characterize the kinetics and specificity of these amine uptake systems.

Main Methods:

• Uptake assays of radiolabeled histamine and 5-HT into isolated mast cell granules.
• Kinetic analysis (Km, Vmax) of saturable transport.
• Inhibition studies using competing amines (5-HT, dopamine, tyramine), ammonium ions, and reserpine.

Main Results:

• Histamine uptake is saturable, pH-dependent, with Km = 91.1 µM and Vmax = 95.4 pmol/(mg protein)/min.
• 5-HT, dopamine, and tyramine competitively inhibit histamine uptake.
• 5-HT uptake exhibits both saturable (Km = 1.6 µM) and nonsaturable components, and is also pH-dependent and inhibited by ammonium ions.
• Reserpine inhibits histamine uptake at nanomolar concentrations.

Conclusions:

• Mast cell granules possess distinct, saturable transport systems for amines.
• Histamine transport involves a system shared with serotonin and dopamine.
• Serotonin and dopamine may utilize additional transport systems.