Desensitization of the histamine H 1 ‐receptor and transcriptional down‐regulation of histamine H 1 ‐receptor gene expression in bovine tracheal smooth muscle

1 We have investigated the role of protein kinase C (PKC) in the desensitization of histamine H 1 ‐receptors and in the expression of the histamine H 1 ‐receptor gene in airway smooth muscle. 2 Prolonged 4β‐phorbol 12,13 dibutyrate (PDBu) pretreatment (4 h, 100 n m –1 μ m ) of bovine trachealis caused a concentration‐dependent loss of contraction in response to histamine H 1 ‐receptor stimulation, which was associated with a concentration‐dependent decrease in histamine‐induced total [ 3 H]‐inositol phosphates accumulation. In contrast, the responses to sodium fluoride, a direct G‐protein activator, were unalterd by PDBu (100–300 n m ) pre‐incubation and only slightly reduced following incubation with 1 μ m PDBu. 3 A selective PKC inhibitor, GF 109203X, partially blocked the PDBu (1 μ m )‐induced desensitization and completely blocked the effect of 100 n m PDBu, confirming the involvement of PKC. 4 Binding experiments using [ 3 H]‐pyrilamine revealed a class of high‐affinity binding sites within the range for the histamine H 1 receptor in airway smooth muscle. PDBu (1 μ m ) pretreatment for 4 h did not change the number of histamine H 1 receptors. 5 PDBu (1 μ m ) exposure caused a time‐dependent reduction in the steady‐state levels of histamine H 1 ‐receptor mRNA, which was inhibited by pre‐incubation with GF 109203X and by cycloheximide, a protein synthesis inhibitor. 6 Nuclear run‐on assays revealed a 50% reduction in the rate of histamine H 1 ‐receptor gene transcription after 17 h PDBu pretreatment, whereas mRNA stability was not affected by PDBu pretreatment (17 h). 7 In conclusion, we have shown a PKC‐mediated desensitization of the histamine H 1 ‐receptor in BTSM and a transcriptional down‐regulation of the histamine H 1 ‐receptor gene expression, which requires new protein synthesis.British Journal of Pharmacology (1998) 125 , 1477–1484; doi: 10.1038/sj.bjp.0702222