Non Channel Function of Kv2.1 to Facilitate Exocytosis; Underlying Molecular Mechanism

Abstract

Classically, voltage-gated potassium channels are viewed as inhibitors of exocytosis by hyperpolarizing membrane potential which is potassium flux-dependent. Recently, we identified a new role for Kv2.1 channels in facilitating vesicle release from neuroendocrine cells, as well as from soma of neurons 1-3. Importantly, this Kv2.1-induced facilitation is potassium flux-independent and is mediated by direct association of Kv2.1 C1a domain with syntaxin. Accordingly, the physical interaction of native Kv2.1 with syntaxin was shown to be dynamic and enhanced during Ca2+- triggerring1,2; impairment of the interaction attenuated release under conditions of no potassium flux2. Further, it was shown3 that the facilitation of exocytosis was mediated by an increase in total number of exocytotic events due to enhanced rate of vesicle recruitment during high Ca2+. Hence, it was suggested that Kv2.1 belongs to a group of proteins that regulate vesicles recruitment by virtue of their direct interaction with syntaxin 4,5.Since Kv2.1 was shown by us to interact with both the open conformation of syntaxin and the binary t-SNARE complex, but not with the ternary SNARE complex, we hypothesized that Kv2.1 stabilization of open syntaxin and/or the t-SNARE complex underlies the Kv2.1-induced recruitment of vesicles. To investigate this hypothesis, we now utilize a probe, constructed by us, that reports, through fluorescence resonance energy transfer (FRET), conformational changes of t-SNAREs with regard to induction of exocytosis via the opening of voltage gated calcium channels in intact PC12 cells.1. Singer-Lahat et al. J Neurosci27 (2007).2. Singer-Lahat et al. PLoS ONE3 (2008).3. Feinshreiber et al. J Cell Sci123 (2010).4. Feinshreiber et al. Ann N Y Acad Sci1152 (2009).5. Mohapatra et al. Sci STKE2007 (2007).