The large-conductance calcium- and voltage-activated K⁺ (BK) channel has a requirement of high intracellular free Ca²⁺ concentrations for its activation in neurons under physiological conditions. The Ca²⁺ sources for BK channel activation are not well understood. In this study, we showed by coimmunopurification and colocalization analyses that BK channels form complexes with NMDA receptors (NMDARs) in both rodent brains and a heterologous expression system. The BK–NMDAR complexes are broadly present in different brain regions. The complex formation occurs between the obligatory BKα and GluN1 subunits likely via a direct physical interaction of the former’s intracellular S0–S1 loop with the latter’s cytosolic regions. By patch-clamp recording on mouse brain slices, we observed BK channel activation by NMDAR-mediated Ca²⁺ influx in dentate gyrus granule cells. BK channels modulate excitatory synaptic transmission via functional coupling with NMDARs at postsynaptic sites of medial perforant path-dentate gyrus granule cell synapses. A synthesized peptide of the BKα S0–S1 loop region, when loaded intracellularly via recording pipette, abolished the NMDAR-mediated BK channel activation and effect on synaptic transmission. These findings reveal the broad expression of the BK–NMDAR complexes in brain, the potential mechanism underlying the complex formation, and the NMDAR-mediated activation and function of postsynaptic BK channels in neurons.

大电导的钙激活和电压激活的K ⁺（BK）通道需要较高的细胞内游离Ca ²⁺浓度，才能在生理条件下激活神经元。Ca ²⁺BK通道激活的来源尚不清楚。在这项研究中，我们通过共免疫纯化和共定位分析表明，在啮齿动物的大脑和异源表达系统中，BK通道均与NMDA受体（NMDAR）形成复合体。BK-NMDAR复合物广泛存在于不同的大脑区域。复杂的形成发生在必需的BKα和GluN1亚基之间，可能是通过前者的细胞内S0–S1环与后者的胞质区直接物理相互作用而形成的。通过膜片钳记录在小鼠脑切片上，我们观察到NMDAR介导的Ca ²⁺激活BK通道流入齿状回颗粒细胞。BK通道通过与内侧穿孔路径齿状回颗粒细胞突触的突触后位点与NMDAR的功能耦合来调节兴奋性突触传递。通过记录移液器将BKαS0–S1环区的合成肽细胞内装载后，将消除NMDAR介导的BK通道激活并影响突触传递。这些发现揭示了BK-NMDAR复合物在脑中的广泛表达，复合物形成的潜在机制以及NMDAR介导的神经元突触后BK通道的激活和功能。