Agonist‐induced desensitization of histamine Hi receptor‐mediated inositol phospholipid hydrolysis in human umbilical vein endothelial cells

Abstract

The regulation of histamine‐induced [3H]‐inositol phosphate formation was studied in human cultured umbilical vein endothelial cells (HUVEC). Histamine (EC50 4.8 μm) produced a 12.7 fold increase in [3H]‐inositol phosphate formation over basal levels. Prior exposure to 0.1 mm histamine (2h) produced a 78% reduction in the response to subsequent histamine (0.1 μm) challenge. The IC50 for this histamine‐induced desensitization was 0.9 μm. The inositol phosphate response to histamine (0.1 μm) was inhibited by phorbol dibutyrate (IC50 40 nm; maximal reduction 64%). This effect was antagonized by both staurosporine (100 nm) and Ro 31–8220 (10 μm). However, the histamine‐induced desensitization of the H1‐receptor‐mediated inositol phosphate response was insensitive to the protein kinase inhibitors, staurosporine, Ro 31–8220, K252a and KN62. Prior exposure to sodium nitroprusside (100 μm), forskolin (10 μm) or dibutyryl cyclic AMP (1 μm) had no effect upon histamine‐induced [3H]‐inositol phosphate formation. NaF (20 μm) and thrombin (EC50 0.4 u ml−1) also induced inositol phosphate formation in HUVEC. Histamine pretreatment (0.1 mm, 10‐120min) failed to modify the inositol phosphate response to a subsequent NaF or thrombin challenge. We conclude that the desensitization of histamine Hrreceptor‐mediated [3H]‐inositol phosphate formation occurs at the level of the receptor and involves a mechanism independent of activation of protein kinase A, G, or C, or calcium calmodulin‐dependent protein kinase II. 1994 British Pharmacological Society