Developmental regulation of the A-type potassium-channel current in hippocampal neurons: Role of the Kvβ1.1 subunit

The rapidly inactivating A-type K⁺ current (I_A) is prominent in hippocampal neurons; and the speed of its inactivation may regulate electrical excitability. The auxiliary K⁺ channel subunit Kvβ1.1 confers fast inactivation to Shaker-related channels and is postulated to affect I_A. Whole-cell patch clamp recordings of rat hippocampal pyramidal neurons in primary culture showed a developmental decrease in the time constant of inactivation (τ_in) of voltage-gated K⁺ currents: 17.9±1.5 ms in young neurons (5-7 days in vitro; n=53, mean±S.E.M.); 9.9±1.0 ms in mature neurons (12-15 days in vitro; n=72, mean±S.E.M., P<0.01). During the same developmental time, the level of Kvβ1.1 transcript increased more than two-fold in vitro and in vivo, determined by semi-quantitative reverse transcriptase-polymerase chain reaction for hippocampus. The hypothesis that up-regulation of Kvβ1.1 led to the changes in τ_in was tested in vitro, using antisense knockdown. Kvβ1.1-specific antisense DNA was introduced with a modified herpes virus co-expressing enhanced green fluorescent protein and knockdown of Kvβ1.1 was verified by immunocytochemistry. Following transduction with the antisense virus, mature neurons reverted to τ_in values characteristic of young neurons: 18.3±2.4 ms (n=20). The effect of antisense knockdown on electrical excitability was tested using current-clamp protocols to induce repetitive firing. Treatment with the antisense virus increased the interspike interval over a range of membrane depolarization (baseline membrane potential=-40 to +20 mV). This effect was most pronounced at -40 mV, where the ISI of the first pair of action potentials was nearly doubled. These data indicate that Kvβ1.1 contributes to the developmental control of I_A in hippocampal neurons and that the magnitude of effect is sufficient to regulate electrical excitability. Viral-mediated antisense knockdown of Kvβ1.1 is capable of decreasing the electrical excitability of post-mitotic hippocampal neurons, suggesting this approach has applicability to gene therapy of neurological diseases associated with hyperexcitability.