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Ion channels are regulated by a host of factors, including membrane potential, ligands, intracellular messengers and, perhaps less obviously, SNARE proteins that control membrane fusion. The t-SNARE syntaxin 1a, for example, regulates the cAMP-dependent C1- channel CFTR, N-type Ca2+ channels and K+ channels. But does such regulation involve a direct effect on channel gating or indirect effects on membrane trafficking? Deborah Nelson and co-workers have examined the mechanism by which syntaxin 1a regulates CFTR activity. They demonstrate that syntaxin 1a directly interacts with CFTR and decreases the open probability (Po) of the channel in excised inside-out patches from airway epithelial cells. Since membrane capacitance (which provides a measure of changes in cell surface area and hence exocytosis/endocytosis) is unaffected by syntaxin 1a, the authors convincingly rule out an effect of membrane trafficking. They speculate that a direct protein-protein interaction is a common mechanism for regulation of ion channels by SNAREs, suggesting that coordination of ion channel activity and membrane fusion could be advantageous in certain cells.
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