Intracellular QX-314 blocks the hyperpolarization-activated inward current I(q) in hippocampal CA1 pyramidal cells

1. Whole cell voltage-clamp recordings (access resistance ≤12 MΩ) from CA1 pyramidal cells in the guinea pig hippocampal slice revealed a hyperpolarization-activated inward current with an inward tail upon repolarization. The current activation range extended from approximately -50 mV to -130 mV, with half-activation at -86 mV. This current was identified as the q current (I(q)). 2. Intracellular QX-314 (5 or 10 mM), a quaternary derivative of lidocaine, blocked I(q) completely throughout its activation range. 3. There is a growing realization that I(q) may be responsible for the pacemaker depolarization in cells that display rhythmic calcium spikes. Because QX-314 blocks I(q) completely, it could be used to test whether I(q) is essential to this oscillatory activity.