Fig. 1.

HA caused biphasic responses that could be mimicked by agonists for its different receptor subtypes. Here and in the similar figures hereafter, the traces represent membrane potentials recorded under current clamp. The arrows underneath the names of agonist indicate the time points when the agonists were ejected. With respect to HA-evoked biphasic membrane voltage shifts (A), BH (histamine receptor H1 agonist) mimicked only the depolarization portion (B), whereas H2 agonist dimaprit (C) and H3 agonist imetit (D) mimicked only the hyperpolarization. Superposition of HA biphasic response (lighter traces) with either BH depolarization (E) or dimaprit hyperpolarization (F) shows that the time courses of the respective responses resembled closely but differed between the two types of responses. The voltage/time scale in A applies to all traces.