We investigated the characteristics of the histamine H1-receptor in cultured rabbit chondrocytes. Scatchard analysis of [3H]pyrilamine, an H1-antagonist, binding to the chondrocytes revealed a single class of binding sites with KD and Bmax values of 90 +/- 12 nM and 56 +/- 11 fmol/10(4) cells, respectively. H1-agonists stimulated the production of keratan sulfate in a dose-dependent manner. Stimulation of keratan sulfate production was inhibited by pyrilamine. Protein kinase C inhibitors (sphingosine and H-7) also had inhibitory effects. Phorbol 12,13-dibutyrate, a direct activator of protein kinase C, activated the production. When protein kinase C in the chondrocytes was down-regulated by preincubation with phorbol ester, the effect of the H1-agonist on keratan sulfate production was abolished. These results indicate that the histamine H1-receptor on chondrocytes mediates the accumulation of keratan sulfate production and that protein kinase C is involved in these events.
Protein kinase C-mediated histamine H1 receptor desensitization through direct phosphorylation of the receptor
