Hyperpolarizing inward rectification in rat neocortical neurons located in the superficial layers

Intracellular recordings were performed in neurons located in layers II/III of rat neocortical slices maintained in vitro. High intensity negative current pulses elicited hyperpolarizing responses that were characterized by a sag of membrane potential towards the resting level. Graphically, this inward rectification was reflected as a break in the slope of the I-V plot at membrane level of around -98 mV. The inward rectification was only partially reduced by the bath perfusion of Cs+ (3 mM). In contrast, it was abolished by the extracellular addition of Ba2+ (3 mM) or the intracellular injection of QX-314 (50 mM). Our findings indicate that Ba2+ and QX-314 are more effective than Cs+ in blocking the hyperpolarizing inward rectification generated by rat neocortical cells located in the superficial layers.