Background
Histamine is a double-protonated molecule with corresponding pKa values of 5.8 and 9.4. Therefore, at physiological pH, histamine exists as an equilibrium mixture of tautomeric cations: the monocation making up 96%, the dication only 3% and the rest being nonprotonated histamine. As a protonated molecule histamine most probably uses a carrier protein in order to cross the cell membrane. In the present work we wanted to determine the kinetic properties of histamine uptake and the influence of other biogenic amines on its transport.