Histamine as a ligand in blood plasma. Part 3. Potentiometric study and simulated distribution of the zinc–histamine ternary complexes with cysteinate, histidinate, glutaminate, threoninate, and citrate

Abstract

Knowing about the distribution of the metal–histamine complexes in blood plasma may help to understand some of the interactions between metal ions and histamine which have been observed in vivo, particularly as far as the influence of zinc and copper is concerned on the physiological activity of this mediator. With this in mind, the present work deals with the experimental determination of the formation constants of the most predominant zinc–histamine ternary species, as predicted from a previous study. Accordingly, the ternary zinc–histamine systems formed with cysteinate, histidinate, glutaminate, threoninate, and citrate were investigated at 37 °C and I= 0.15 mol dm^–3 Na[ClO₄]. Interpretations derived from the simulated distribution of these complexes in the presence of the interfering copper–histamine–histidinate species are given, concerning a possible mode of action for zinc and copper towards histamine in vivo.