Characterization of functional histamine H1 receptors on a cultured smooth muscle cell line

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Abstract
Cultured cells of the smooth muscle line DDT1MF‐2, which was derived from a hamster vas deferens tumor, expressed histamine H1‐type receptors and responded biochemically and functionally to H1‐specific stimulation. The H1‐receptor antagonist [3H]‐pyrilamine bound specifically to 9.7 × 106 sites/DDT1MF‐2 cell with a dissociation constant (Kd) of 219 nM. The addition of histamine to suspensions of fura‐2‐loaded DDT1MF‐2 cells elicited a rapid, transient, and stimulus concentration‐dependent increase in the intracellular concentration of Ca2+ with an EC50 of 3 × 10−5 M, which demonstrated H1 receptor specificity. Moreover, in order to evaluate in vitro contractile response of individual DDT1MF‐2 cells, the degree of intracellular actin polymerization was quantified by a DNase inhibition assay. The percentage of nonpolymerized or G‐actin in DDT1MF‐2 cells was reduced in a histamine concentration‐dependent manner with an EC50 of 1 × 10−5 M and H1 receptor specificity. Histamine‐induced actin polymerization was accompanied by changes in cell shape that were consistent with cellular contraction, as assessed by flow cytometry. The H1‐type receptors of cultured DDT1MF‐2 cells thus couple histamine stimulation to a variety of functional responses of smooth muscle cells.