Presence of histamine H2-receptors on human gastric carcinoma cell line MKN-45 and their increase by retinoic acid treatment. 
Histamine dose-dependently stimulated cyclic AMP production in human gastric carcinoma cell line MKN-45, and this effect was inhibited by cimetidine but not by pyrilamine.  Moreover, not only histamine but also cimetidine displaced the specific binding of [3H]tiotidine to these cells, whereas pyrilamine had no effect.  On the other hand, pretreatment of MKN-45 cells with retinoic acid (RA) significantly enhanced histamine-induced increase of cyclic AMP production, although the cyclic AMP response to either forskolin or NaF was not affected.  Finally, RA treatment increased the number of histamine receptor without altering its affinity.  Thus, it appears that histamine H2-receptors are present on MKN-45 cells, and that RA treatment enhances the action of histamine on these cells by increasing the number of H2-receptors.