Desensitization of the histamine H-1-receptor and transcriptional down-regulation of histamine H-1-receptor gene expression in bovine tracheal smoothmuscle

1 We have investigated the role of protein kinase C (PKC) in the desensitiz ation of histamine H-1-receptors and in the expression of the histamine H-1 -receptor gene in airway smooth muscle. 2 Prolonged 4 beta-phorbol 12,13 dibutyrate (PDBu) pretreatment (4h, 100 mM -1 mu M) of bovine trachealis caused a concentration-dependent loss of cont raction in response to histamine H-1-receptor stimulation, which was associ ated with a concentration-dependent decrease in histamine-induced total [H- 3]-inositol phosphates accumulation. In contrast, the responses to sodium f luoride, a direct G-protein activator, were unalterd by PDBu (100-300 nM) p re-incubation and only slightly reduced following incubation with 1 mu M PD Bu. 3 A selective PKC inhibitor, CF 109203X, partially blocked the PDBu (1 mu M )-induced desensitization and completely blocked the effect of 100 nM PDBu, confirming the involvement of PKC. 4 Binding experiments using [H-3]-pyrilamine revealed a class of high-affin ity binding sites within the range for the histamine H-1 receptor in airway smooth muscle. PDBu (1 mu M) pretreatment for 4 h did not change the numbe r of histamine H-1 receptors. 5 PDBu (1 mu M) exposure caused a time-dependent reduction in the steady-st ate levels of histamine H-1-receptor mRNA, which was inhibited by pre-incub ation 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 s tability,was not affected by PDBu pretreatment (17 h). 7 In conclusion, we have shown a PKC-mediated desensitization of the histam ine H-1-receptor in BTSM and a transcriptional down-regulation of the hista mine H-1-receptor gene expression, which requires new protein synthesis.