CHARACTERIZATION OF COEXISTENT HISTAMINE H1-RECEPTOR AND H2-RECEPTOR BINDING-SITES IN THE PURIFIED GUINEA-PIG MYOCARDIAL MEMBRANES FROM VENTRICLES

In the present work, we identified and characterised histamine H1- and H 2-receptors in highly purified myocardial membranes isolated from f emale guinea pig ventricles. We determined the binding parameters for the interactions of H-3-mepyramine with the histamine H1-receptor bind ing site and H-3-tiotidine with the histamine H2-receptor binding site . Binding of both ligands in our study was saturable, reversible and o f high affinity. Scatchard's analysis of the specific H-3-mepyramine b inding revealed the existence of high and low affinity binding sites w ith apparent K(D) values of 0.4 nM and 4.5 nM, respectively. The densi ty of binding sites (B(max)) was 100 fmol/mg protein for the high and 466 fmol/mg protein for the low affinity binding site. H-3-tiotidine b inds to a single population of binding sites with a K(D) of 1.0 nM and a B(max) of 27 fmol/mg protein. These data suggest that both histamin e H1- and H2-receptors coexist in the guinea pig myocardium with a sig nificantly higher prevalence of the histamine H1-receptor population.