Comparison of the endogenous IK currents in rat hippocampal neurons and cloned Kv2.1 channels in CHO cells

The Kv2.1 potassium channel is a principal component of the delayed rectifier IK current in the pyramidal neurons of cortex and hippocampus. We used whole-cell patch-clamp recording techniques to systemically compare the electrophysiological properties between the native neuronal IK current of cultured rat hippocampal neurons and the cloned Kv2.1 channel currents in the CHO cells. The slope factors for the activation curves of both currents obtained at different prepulse holding potentials and holding times were similar, suggesting similar voltage-dependent gating. However, the half-maximal activation voltage for IK was ∼20 mV more negative than the Kv2.1 channel in CHO cells at a given prepulse condition, indicating that the neuronal IK current had a lower threshold for activation than that of the Kv2.1 channel. In adddition, the neuronal IK showed a stronger holding membrane potential and holding time-dependence than Kv2.1. The Kv2.1 channel gave a U-shaped inactivation, while the IK current did not. The IK current also had much stronger voltage-dependent inactivation than Kv2.1. These results imply that the neuronal factors could make Kv2.1 channels easier to activate. The information obtained from these comparative studies help elucidate the mechanism of molecular regulation of the native neuronal IK current in neurons.