PT  - JOURNAL ARTICLE
AU  - M Mitsuhashi
AU  - T Mitsuhashi
AU  - P F Dazin
AU  - D G Payan
TI  - Agonistic activities of histamine-albumin conjugates at histamine H2 receptors on human HL-60 promyelocytic leukemia cells.
DP  - 1991 Aug 01
TA  - Molecular Pharmacology
PG  - 271--275
VI  - 40
IP  - 2
4099  - http://molpharm.aspetjournals.org/content/40/2/271.short
4100  - http://molpharm.aspetjournals.org/content/40/2/271.full
SO  - Mol Pharmacol1991 Aug 01; 40
AB  - We previously identified functional histamine H2 receptors on human HL-60 promyelocytic leukemia cells [J. Biol. Chem. 264: 18356-18362 (1989)]. In the present study, we have compared the action of histamine-albumin conjugates on H2 receptor activation with that of histamine alone. Both histamine and conjugates increased intracellular levels of Ca2+ in an H2 receptor-specific manner. However, binding of fluoresceinated histamine-albumin conjugates to HL-60 cells was not dissociated by 10(-4) M unlabeled histamine, although this concentration of histamine significantly desensitized conjugate responses. These data suggest that histamine-albumin conjugates not only activate H2 receptors but also bind to HL-60 cells nonspecifically or in an H2 receptor-unrelated manner. Moreover, histamine-induced Ca2+ mobilization was transient, whereas conjugate-induced Ca2+ mobilization was sustained for more than 10 min, as a result of the influx of extracellular Ca2+. Therefore, the functional difference between histamine and conjugates may provide a good model for the further understanding of the activation mechanisms of receptor-operated Ca2+ influx.