Voltage-gated Kvl.1/Kvβ.1 A-type channels, as a natural complex, can switch from fast to slow inactivation under oxidation! reduction conditions. The mode-switching of inactivation, which is mediated by a cysteine residue in the inactivation ball domain of the Kvlβ1.1 N terminus, can regulate membrane electrical excitability. In the present study, we identified a mechanism whereby inactivation in Kvl.1/Kvβ1.1 channels is regulated by calcium influx. The rise in intracellular calcium, due to either influx from extracellular space or release from intracellular stores, eliminates fast inactivation induced by Kvβ1.1, resulting in slower inactivation and increased steady-state current. This oxidation-independent calcium effect is mediated through the Kvβ1.1 N terminus, not the C terminus. We propose that a coupling between calcium influx and inactivation of voltage-gated A-type K+ channels occurs as a result of membrane depolarization and may contribute to after- hyperpolarization as negative feedback to control neuronal excitability. [ABSTRACT FROM AUTHOR]