Figure 6. The excitatory effects of the histamine agonists on human submucous neurones were specific with no indication of cross-reactivity.
A–B, the responses to pressure application of the H1 agonist HTMT-dimaleat (black bars) remained in the presence of the H2 antagonist ranitidine (A) or the H3 antagonist clobenpropit (B). C–D, likewise the responses to pressure application of the H2 agonist dimaprit (black bars) remained in the presence of the H1 antagonist pyrilamine (C) or the H3 antagonist clobenpropit (D). E–F, the responses to pressure application of the H3 agonist (R)-(−)-α-methylhistamine (black bars) remained in the presence of the H1 antagonist pyrilamine (E) or the H2 antagonist ranitidine (F). The deflections in the traces during application of the agonists are pressure ejection artefacts. Traces in A–E were from different neurones. Scale bars represent time (0.5 s) and changes in fluorescence intensity (ΔF/F = 0.1%). Note that underlying slow depolarizations of membrane potential are not detected by the AC-coupled photodiode system.