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KCNQ‐SMIT complex formation facilitates ion channel‐solute transporter cross talk

Voltage‐gated potassium channels formed by KCNQ2 and KCNQ3 are essential for normal neuronal excitability. KCNQ2/3 channel activity is augmented in vivo by phosphatidylinositol 4,5‐bisphosphate (PIP2), which is generated from myo‐inositol, an osmolyte transported into cells by sodium‐dependent myo‐inositol transporters (SMITs). Here, we discovered that KCNQ2/3 channels isoform‐specifically colocalize with SMIT1 and SMIT2 at sciatic nerve nodes of Ranvier and in axon initial segments, and form channel–transporter complexes in vitro and in vivo. KCNQ2/3 coexpression protected SMIT1 activity from the otherwise inhibitory effects of cellular depolarization imposed by elevating extracellular [K+], and KCNQ2 was required for potentiation of SMIT activity by myo‐inositol preincubation. Cytoskeletal disruption, which speeds PIP2 dispersion, attenuated potentiation of KCNQ2/3 currents by SMIT1‐mediated myo‐inositol uptake, suggesting close channel–transporter juxtaposition ensures KCNQ2/3 exposure to locally high myo‐inositol‐derived PIP2 concentrations. Thus, KCNQ2/3‐SMIT1/2 coassembly permits cross talk via physical interaction, and may also be required for optimal, reciprocal indirect regulation via membrane potential and PIP2, especially within the specialized architecture of axons.—Neverisky, D. L., Abbott, G. W. KCNQ‐SMIT complex formation facilitates ion channel‐solute transporter cross talk. FASEB J. 31, 2828–2838 (2017). www.fasebj.org