Calcium Influx via L- and N-Type Calcium Channels Activates a Transient Large-Conductance Ca2+-Activated K+Current in Mouse Neocortical Pyramidal Neurons

摘要

Ca²⁺-activated K⁺ currents and their Ca²⁺ sources through high-threshold voltage-activated Ca²⁺ channels were studied using whole-cell patch-clamp recordings from freshly dissociated mouse neocortical pyramidal neurons. In the presence of 4-aminopyridine, depolarizing pulses evoked transient outward currents and several components of sustained currents in a subgroup of cells. The fast transient current and a component of the sustained currents were Ca²⁺ dependent and sensitive to charybdotoxin and iberiotoxin but not to apamin, suggesting that they were mediated by large-conductance Ca²⁺-activated K⁺ (BK) channels. Thus, mouse neocortical neurons contain both inactivating and noninactivating populations of BK channels. Blockade of either L-type Ca²⁺ channels by nifedipine or N-type Ca²⁺ channels by ω-conotoxin GVIA reduced the fast transient BK current. These data suggest that the transient BK current is activated by Ca²⁺entry through both N- and L-type Ca²⁺ channels. The physiological role of the fast transient BK current was also examined using current-clamp techniques. Iberiotoxin broadened action potentials (APs), indicating a role of BK current in AP repolarization. Similarly, both the extracellular Ca²⁺ channel blocker Cd²⁺ and the intracellular Ca²⁺chelator BAPTA blocked the transient component of the outward current and broadened APs in a subgroup of cells. Our results indicate that the outward current in pyramidal mouse neurons is composed of multiple components. A fast transient BK current is activated by Ca²⁺ entry through high-threshold voltage-activated Ca²⁺ channels (L- and N-type), and together with other voltage-gated K⁺ currents, this transient BK current plays a role in AP repolarization.