Inhibition of ROMK potassium channel by syntaxin 1A

ROMK potassium channels are present in the cortical collecting duct (CCD) of the kidney and serve as apical exit pathways for K⁺ secretion in this nephron segment. K⁺ secretion in the CCD is regulated by multiple factors. In this study, we show that syntaxin 1A, but not syntaxin 3 or 4, inhibited whole cell ROMK currents in Xenopus laevis oocytes. Syntaxin 1A. but not syntaxin 3 or 4, interacted with the COOH-terminal cytoplasmic domain of ROMK in intro. Coexpression with synaptobrevin 2 reversed inhibition of whole cell ROMK currents by syntaxin 1A. In excised inside-out membranes of oocytes, application of fusion proteins containing the cytoplasmic region of syntaxin 1A to the cytoplasmic face caused a dose-dependent inhibition of ROMK. We further examined regulation of the K⁺ channels in the CCD by syntaxin 1A. Application of botulinum toxin Cl to the excised inside-out membranes of the CCD caused an increase in the activity of K⁺ channels. In contrast, application of toxin B had no effects. These results suggest that syntaxin 1A causes a tonic inhibition of the K⁺ channels in the apical membrane of the CCD. Binding of synaptobrevin 2 to syntaxin 1A during docking and fusion of transport vesicles to the plasma membranes of CCD may lead to activation of these channels.