Figure 1. Estimating the reversal potential (I_rev) of I_h in area postrema neurons.

A, slowly activated inward current elicited by hyperpolarizing step pulses (upper traces). Interval between voltage step commands: 3 s in this and subsequent figures. The holding potential was −60 mV in this and subsequent voltage-clamp recordings. An ‘instantaneous’ current (I_in) was measured at the point marked •. A ‘steady state’ current (I_ss) was measured at the end of the voltage steps (▴). B, hyperpolarizing prepulses and following step pulses (upper traces) elicited deactivation of I_h. The interval between voltage step commands was 4 s; I_in was measured at the point marked ○. C, plots of I_in obtained in the experiments shown in A (•) and B (○) against the membrane potential (n = 19). The dashed line indicates the value of the membrane potential (−35.9 mV) at the intersection of the two regression lines, which corresponds to the V_rev of I_h. All recordings were made in ACSF containing TEA, Ba²⁺, 4-AP, TTX and nominally zero Ca²⁺ (see Methods).