[H-3] MEPYRAMINE BINDING-SITES, HISTAMINE H1-RECEPTORS, IN BOVINE RETINAL BLOOD-VESSELS

The presence of histamine H-1-receptors in the bovine retinal blood vessels was studied with a [H-3]mepyramine binding assay. The membranes of purified vessels obtained from bovine retinas showed specific [H-3]mepyramine binding sites with a dissociation constant (K(D)) of 2.78 +/- 0.32 nM. This was similar to values obtained from the retinal neuronal fractions. The binding capacity (BMax) was 53.8 +/- 1.7 fmol/mg protein, which was about a half that of the retinal neuronal fractions (108.9 +/- 3.1 fmol/mg protein). Some H-1-antagonists proved to be potent competitors for [H-3]mepyramine binding sites in bovine retinal blood vessels. These results indicate that histamine H-1-receptors exist in the retinal blood vessels which may be involved in the physiological and the pathological responses of blood circulation in retinas.