Signalling pathway for histamine activation of non-selective cation channels in equine tracheal myocytes

摘要

class="enumerated" style="list-style-type:decimal">The signalling pathway underlying histamine activation of non-selective cation channels was investigated in single equine tracheal myocytes. Application of histamine (100 μM) activated the transient calcium-activated chloride current (ICl(Ca)) and sustained, low amplitude non-selective cation current (ICat). The H1 receptor antagonist pyrilamine (10 μM) blocked activation of ICl(Ca) and ICat. Simultaneous application of histamine (100 μM) and caffeine (8 mm) during H1 receptor blockade activated ICl(Ca), but not ICat. Neither the H2 receptor antagonist cimetidine (20 μM) nor the H3 receptor antagonist thioperamide (20 μM) prevented activation of ICl(Ca) and ICat.Intracellular dialysis of anti-Gαi/Gαo antibodies completely blocked activation of ICat by histamine, whereas ICl(Ca) was not affected. By contrast, anti-Gα_q/Gα₁₁ antibodies greatly inhibited I_Cl(Ca), but did not alter activation of I_Cat.1-Oleoyl-2-acetyl-sn-glycerol (OAG, 20–100 μM) did not induce any current or affect currents activated by histamine or methacholine (mACH). Simultaneous application of OAG and caffeine activated I_Cl(Ca), but not I_Cat, indicating that a rise in [Ca²⁺]_i and stimulation of diacylglycerol-sensitive protein kinase C (PKC) is not sufficient to activate I_Cat. The phospholipase C inhibitor (2 μM) blocked histamine activation of I_Cl(Ca) and I_Cat, but simultaneous exposure of myocytes to histamine and caffeine restored both I_Cl(Ca) and I_Cat in the presence of .Histamine and mACH activated currents with equivalent I–V relationships. The currents activated by these agonists were not additive; following activation of I_Cat by mACH, histamine failed to induce an additional membrane current. Similarly, mACH did not induce an additional current after full activation of I_Cat by histamine.We conclude that H₁ histamine receptors activate I_Cat through coupling to G_i/G_o proteins. Activation of I_Cat also requires intracellular calcium release, mediated by H₁ receptors coupling to G_q/G₁₁ proteins. This coupling is analogous to the activation of I_Cat by co-stimulation of M₂ and M₃ receptors.