Desensitization of histamine H1 receptor‐mediated inositol phosphate production in HeLa cells
Authors: Bristow David R. , Zamani M. Reza 
Published: July 2012

Histamine stimulated the accumulation of total [3H]‐inositol phosphates (IPn) in control HeLa cells with an EC50 of 3.7 ± 0.7 μm in the presence of 10 mm LiCl. The maximum response to histamine after 15 min incubation was 43 ± 5% over basal accumulation and occurred at a concentration of 1 mm histamine.
The histamine‐induced IPn production in HeLa cells was confirmed as H1 receptor‐mediated, since the H1 antagonist mepyramine (10−6 m) inhibited the histamine response (10−4 m) by 83 ± 7%, whereas the H2 antagonist, ranitidine (10−4 m), and H3 antagonist, thioperamide (10−6 m), were ineffective.
Histamine (10−4 m) pretreatment of HeLa cells for 30 min desensitized the subsequent histamine‐induced IPn accumulation. The desensitized cells accumulated IPn in response to histamine with an EC50 of 1.7 ± 0.7 μm after 15 min incubation. The maximum histamine‐induced IPn accumulation at 10−4 m was 19 ± 5% over basal and was significantly lower (P < 0.03) than the maximum response in control cells.
The desensitization of histamine‐induced IPn accumulation was time‐dependent and, at a desensitizing histamine concentration of 10−4 m, the half‐maximal attenuation occurred after approximately 9 min and maximum desensitization was achieved by 15–20 min. The desensitization of the IPn accumulation was a reversible phenomenon and full recovery of the response occurred 150 min after the removal of the desensitizing histamine‐containing medium. The half‐time for the recovery of the histamine‐induced response was estimated at 120 min.
Bradykinin stimulated IPn accumulation in HeLa cells, and the EC50 in control cells of 1.9 ± 0.2 nm was not significantly different from the EC50 value from histamine‐pretreated cells of 1.6 ± 0.9 nm. The bradykinin response at 1 μm was 194 ± 48% over basal IPn accumulation in control cells and this value was significantly different (P < 0.04) from the 1 μm bradykinin‐induced IPn accumulation in histamine‐pretreated HeLa cells of 143 ± 38% over basal.
NaF stimulated IPn accumulation in control HeLa cells in a dose‐related manner, with the maximum effect occurring at 15–20 mm. The EC50 value for NaF‐stimulated IPn accumulation in control cells was 10.5 ± 1.1 mm and the maximum response was 136 ± 41% over basal after 20 min incubation. In histamine desensitized HeLa cells the EC50 value for NaF was 12.3 ± 0.4 mm after 20 min stimulation, which was not significantly different from the value obtained in control cells. The maximum NaF‐stimulated IPn formation in desensitized cells of 68 ± 23% over basal occurred at 15–20 mm and was significantly lower (P < 0.01) than that obtained in control cells.
We show here that the acute histamine pretreatment of HeLa cells results in the desensitization of histamine H1 receptor‐mediated IPn production. The desensitization was not restricted to the H1 receptor‐mediated signal transduction pathway, but also includes both the bradykinin‐ and NaF‐mediated responses, supporting a heterologous desensitization mechanism. Our results are consistent with the site of attenuation being at or distal to the G‐protein and the underlying mechanism being a slowed time‐course for the production of inositol phosphates.