Histamine H1-receptor-mediated inositol phospholipid hydrolysis in DDT1MF-2 cells: agonist and antagonist properties

1. The effect of histamine H1-receptor stimulation on inositol phospholipid hydrolysis has been investigated in the hamster vas deferens smooth muscle cell line, DDT1MF-2. 2. Histamine (EC50 = 27 microM) stimulated the accumulation of [3H]-inositol phosphates in DDT1MF-2 cells prelabelled with [3H]-myo-inositol. 2-Thiazolylethylamine (EC50 42 microM) produced a maximal response of similar magnitude to histamine while the maximal response obtained with N alpha-methylhistamine (EC50 = 72 microM) and 2-pyridylethylamine (EC50 = 85 microM) were much lower (circa 65%, histamine = 100%). 3. The H1-selective agonists 2-(3-fluorophenyl)-histamine (2-FPH) and 2-(3-chlorophenyl)-histamine (2-CPH) both appeared to act as partial H1-agonists in this system. Both compounds produced maximal responses of only 30% (with respect to histamine = 100) and were able to antagonize the inositol phosphate response to histamine (estimated Kp = 10.4 and 18.9 microM for 2-FPH and 2-CPH respectively). 4. The response to histamine was antagonized by the H1-antagonists, mepyramine (KD 0.4 nM), (+)-chlorpheniramine (KD 1.2 nM) and promethazine (KD 0.3 nM). Furthermore, the (-)-isomer of chlorpheniramine was approx. three orders of magnitude less potent than the corresponding (+)-isomer. 5. The response to histamine (0.1 mM) was not altered by prior treatment of cells with pertussis toxin (100 ng ml-1; 24 h) whereas the inositol phosphate response to adenosine A1-receptor stimulation in this cell line was significantly attenuated under these conditions. 6. These data indicate that histamine-stimulated inositol phospholipid hydrolysis in DDT1MF-2 cells is mediated via a classical H1-receptor. Furthermore, the results also suggest that histamine HI- and adenosine A,-receptors activate phospholipase C in DDTMF-2 cells via two different G-protein-coupled pathways.