Electrophysiological properties of the rat area postrema neurons displaying both the transient outward current and the hyperpolarization-activated inward current.

We found coexistence of the transient outward potassium current (I(TO)) and the hyperpolarization-activated inward current (I(H)) in 26 of 82 area postrema neurons tested using the whole-cell patch-clamp technique in rat brain slices. Cells displaying both the I(TO) and the I(H) typically showed "voltage sag" and "rebound potentials" in response to hyperpolarizing current injection and repetitive firing with strong adaptation was seen with depolarizing current injection. When cells were held at membrane potentials more negative than the resting level (e.g., -85mV), the afterhyperpolarization was enhanced. Voltage clamp recordings were performed to examine the characteristics of I(TO) and I(H) in and the contributions of these currents to the electroresponsiveness of area postrema cells. We show, in this study, the voltage-dependent properties of I(H) and I(TO), and how these currents modulate the intrinsic membrane properties of area postrema cells. We discuss the functional significance of the specific subset of area postrema neurons whose cells have both I(H) and I(TO) channels.