Histamine is an important mediator of immediate hypersensitivity for both animals and humans. The action of histamine on target tissues is believed to be mediated by specific cell surface receptors, especially H1 and H2 receptors for hypersensitivity and inflammatory reactions, which involve stimulation of smooth muscle Contractility, alterations in vascular permeability, and modifications in the activities of macre phages and lymphocytes. Although the nature of histamine receptors in the brain and peripheral tissues has been studied extensively by many laboratories, the molecular mechanism of histamine receptor-mediated reactions is not fully understood, mainly because histamine receptors are incompletely characterized from the biochemical point of view. In previous studies, we have found that the cultured smooth muscle cell line DDT,MF-2, derived from hamster vas deferens, expresses low-affinity histamine H 1 receptors and responds biochemically and functionally to H 1-specific stimulation (Mitsuhashi and Payan, J Cell Physiol 134367, 1988). This cell line provides a model for analyzing the biochemical responses of HI receptor-mediated reactions in peripheral tissues. In this review, we summarized our recent progress in the study of low-affinity H1 receptors on DDT,MF-2 cells.
Key words histamine H l receptor, calcium, protein kinase C
Histamine is an important mediator of immediate hypersensitivity for both animals and humans [ 1-31. For example, in healthy human subjects, an intradermal injection of histamine induces a wheal and flare response similar to that seen in urticaria [4]. Inhalation of histamine provokes bronchoconstriction [ 51, and intravenous injection of histamine results in a rapid decrease in blood pressure similar to that seen in anaphylactic shock [ 6 ] . Serum levels of histamine are also increased in patients with hymenoptera-sting hypersensitivity during the acute phase of anaphylactic shock [7]. Moreover, human blood basophilic leukocytes in patients with allergic disorders release histamine in vitro in response to specific and nonspecific stimuli [8].
In mammalian species, histamine is synthesized by histidine decarboxylase [9] and stored in all tissues in amounts ranging from less than 1 pg/g to over 100 pg/g [lo]. Histamine is then released in conjunction with other potent chemical mediators in