INTRACELLULAR QX-314 BLOCKS THE HYPERPOLARIZATION-ACTIVATED INWARD CURRENT I-Q IN HIPPOCAMPAL CA1 PYRAMIDAL CELLS

1. Whole cell voltage-clamp recordings (access resistance less than or equal to 12 M Omega) 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.