Canine histamine H2 receptor DNA, cloned by polymenase chain reaction (PCR), was transfected into Chinese hamster ovary cells using an expression vector. The expression of H2 receptors was demonstrated by immunoblotting with specific antibodies and the binding of tiotidine, an H2 receptor antagonist. H2 receptor-specific cAMP production was observed only in cells expressing canine H2 receptors. Preincubation of transfected cells with 10 microM histamine for 10 or 60 min at 37 degrees C decreased both the maximal response and the sensitivity of the subsequent histamine-stimulated cAMP production, showing desensitization. Under these circumstances, decreases in tiotidine binding without changes in affinity in intact cells and also in the membrane were observed, whereas there was no decrease in total H2 receptor number. Thus, desensitization of histamine H2 receptor was associated with the sequetration of receptors.