AGONIST-INDUCED DESENSITIZATION OF HISTAMINE H-1 RECEPTOR-MEDIATED INOSITOL PHOSPHOLIPID HYDROLYSIS IN HUMAN UMBILICAL VEIN ENDOTHELIAL-CELLS

1 The regulation of histamine-induced [H-3]-inositol phosphate formati on was studied in human cultured umbilical vein endothelial cells (HUV EC). 2 Histamine (EC(50) 4.8 mu M) produced a 12.7 fold increase in [H -3]-inositol phosphate formation over basal levels. Prior exposure to 0.1 mM histamine (2 h) produced a 78% reduction in the response to sub sequent histamine (0.1 mM) challenge. The IC50 for this histamine-indu ced desensitization was 0.9 mu M. 3 The inositol phosphate response to histamine (0.1 mM) was inhibited by phorbol dibutyrate (IC50 40 nM; m aximal reduction 64%). This effect was antagonized by both staurospori ne (100 nM) and Ro 31-8220 (10 mu M). However, the histamine-induced d esensitization of the H-1-receptor-mediated inositol phosphate respons e was insensitive to the protein kinase inhibitors, staurosporine, Ro 31-8220, K252a and KN62. 4 Prior exposure to sodium nitroprusside (100 mu M), forskolin (10 mu M) or dibutyryl cyclic AMP (1 mM) had no effe ct upon histamine-induced [H-3]-inositol phosphate formation. 5 NaF (2 0 mM) and thrombin (EC(50) 0.4 u ml(-1)) also induced inositol phospha te formation in HUEC. Histamine pretreatment (0.1 mM, 10-120 min) fail ed to modify the inositol phosphate response to a subsequent NaF or th rombin challenge. 6 We conclude that the desensitization of histamine H-1-receptor-mediated [H-3]-inositol phosphate formation occurs at the level of the receptor and involves a mechanism independent of activat ion of protein kinase A, G, or C, or calcium calmodulin-dependent prot ein kinase II.