Desensitization of the histamine H₁-receptor and transcriptional down-regulation of histamine H₁-receptor gene expression in bovine tracheal smooth muscle

Abstract

1. We have investigated the role of protein kinase C (PKC) in the desensitization of histamine H₁-receptors and in the expression of the histamine H₁-receptor gene in airway smooth muscle.

2. Prolonged 4β-phorbol 12,13 dibutyrate (PDBu) pretreatment (4 h, 100 nM–1 μM) of bovine trachealis caused a concentration-dependent loss of contraction in response to histamine H₁-receptor stimulation, which was associated with a concentration-dependent decrease in histamine-induced total [³H]-inositol phosphates accumulation. In contrast, the responses to sodium fluoride, a direct G-protein activator, were unalterd by PDBu (100–300 nM) pre-incubation and only slightly reduced following incubation with 1 μM PDBu.

3. A selective PKC inhibitor, GF 109203X, partially blocked the PDBu (1 μM)-induced desensitization and completely blocked the effect of 100 nM PDBu, confirming the involvement of PKC.

4. Binding experiments using [³H]-pyrilamine revealed a class of high-affinity binding sites within the range for the histamine H₁ receptor in airway smooth muscle. PDBu (1 μM) pretreatment for 4 h did not change the number of histamine H₁ receptors.

5. PDBu (1 μM) exposure caused a time-dependent reduction in the steady-state levels of histamine H₁-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 H₁-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 H₁-receptor in BTSM and a transcriptional down-regulation of the histamine H₁-receptor gene expression, which requires new protein synthesis.

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