Colocalization and coassembly of two human brain M-type potassium channel subunits that are mutated in epilepsy

摘要

Acetylcholine excites many central and autonomic neurons through inhibition of M-channels, slowly activating, noninactivat- ing voltage-gated potassium channels. We here provide informa- tion regarding the in vivo distribution and biochemical character- istics of human brain KCNQ2 and KCNQ3, two channel subunits that form M-channels when expressed in vitro, and, when mu- tated, cause the dominantly inherited epileptic syndrome, benign neonatal familial convulsions. KCNQ2 and KCNQ3 proteins are colocalized in a somatodendritic pattern on pyramidal and poly- morphic neurons in the human cortex and hippocampus. Immu- noreactivity for KCNQ2, but not KCNQ3, is also prominent in some terminal fields, suggesting a presynaptic role for a distinct sub- group of M-channels in the regulation of action potential propa- gation and neurotransmitter release. KCNQ2 and KCNQ3 can be coimmunoprecipitated from brain lysates. Further, KCNQ2 and KCNQ3 are coassociated with tubulin and protein kinase A within a Triton X-100-insoluble protein complex. This complex is not associated with low-density membrane rafts or with N-methyl-D- aspartate receptors, PSD-95 scaffolding proteins, or other potas- sium channels tested. Our studies thus provide a view of a signal- ing complex that may be important for cognitive function as well as epilepsy. Analysis of this complex may shed light on the unknown transduction pathway linking muscarinic acetylcholine receptor activation to M-channel inhibition.