Figure 6.
Histamine H2 receptor-mediated inward current and its electrophysiological feature. (A) Concentration–response curve for dimaprit on five recorded MVN neurons shows the mean EC50 of 157.7 μM. (B) The dimaprit-induced inward current was abolished by ranitidine, indicating dimaprit evoked an isolated current associated with the activation of postsynaptic H2 receptors. (C) Group data of the five tested MVN neurons. Data shown are means ± SEM; ***P < 0.001. (D, E) Slow ramp command tests were employed to obtain the I–V curves in the absence and presence of dimaprit (the left panel in D). The difference current representing the dimaprit-induced current (the right panel in D) exhibited a significant feature of hyperpolarization-activated non-selective cation current (via HCN channels). Under a condition of blockage of HCN channels by continuously applying ZD7288, the I–V curves recorded in the absence and presence of dimaprit coincided (the left panel in E) and the dimaprit-induced net current became zero (the right panel in E).