3H-Mepyramine binding and histamine-stimulated cAMP accumulation in mammalian retina

The specific binding of different amounts of³H-mepyramine to the bovine retina revealed a quasi-hyperbolic curve which approached saturation at³H-ligand concentration over 9–12 nM. Scatchard analysis of the binding data showed two binding sites with K_D values of 0.76 nM and 7.3 nM and B_max of 49.3 and 194.6 fmole/mg protein, respectively. In the guinea-pig brain³H-mepyramine bound to a single population of binding sites with K_D value of 1.6 nM and B_max of 291 fmole/mg protein. Various H₁-antihistamines were potent competitors of the³H-mepyramine binding: there was a big difference in potency of d- and 1-chlorpheniramine in both membrane preparations.In the rabbit retina slices histamine, in contrast to dopamine, weakly stimulated cAMP accumulation.The data suggest that the mammalian retina may possess histamine receptors.