Whether interactions between synaptotagmin-1 (syt-1) and the soluble NSF attachment protein receptors (SNAREs) are required during neurotransmission is debated. We examined five SNAP-25 mutations designed to interfere with syt-1 interactions. One mutation, D51/ E52/E55A, targeted negative charges within region II of the primary interface (Zhou et al., 2015); two mutations targeted region I (D166A and D166/E170A) and one mutation targeted both (D51/E52/E55/D166A). The final mutation (D186/D193A) targeted C-terminal residues not expected to interact with syt-1. An in vitro assay showed that the region I, region II, and region IϩII (D51/E52/E55/D166A) mutants markedly reduced the attachment between syt-1 and t-SNARE-carrying vesicles in the absence of phosphatidylinositol 4,5-bisphosphate [PI(4,5)P 2 ]. In the presence of PI(4,5)P 2 , vesicle attachment was unaffected by mutation. When expressed in Snap-25-null mouse autaptic neurons, region I mutations reduced the size of the readily releasable pool of vesicles, whereas the region II mutation reduced vesicular release probability. Combining both in the D51/E52/E55/D166A mutation abrogated evoked release. These data point to a division of labor between region I (vesicle priming) and region II (evoked release). Spontaneous release was disinhibited by region I mutations and found to correlate with defective complexin (Cpx) clamping in an in vitro fusion assay, pointing to an interdependent role of synaptotagmin and Cpx in release clamping. Mutation in region II (D51/E52/E55A) also unclamped release, but this effect could be overcome by synaptotagmin overexpression, arguing against an obligatory role in clamping. We conclude that three synaptic release functions of syt-1, vesicle priming, spontaneous release clamping, and evoked release triggering, depend on direct SNARE complex interaction.

Key points• Transient receptor potential (TRP) A ion channels are evolutionarily conserved and play a fundamental role in thermal, chemical and mechanical transduction.• In this study, we characterized Drosophila TRPA1 as a non-selective cation channel that can be activated by heat, voltage and chemicals.• By constructing the chimeric channel between Drosophila TRPA1 and its cold-sensitive human orthologue, we identified key residues in the transmembrane domain that confer heat sensitivity.• Perturbation of the putative voltage-sensing module increased the threshold for heat activation.• Single channel recordings revealed the reaction schemes of wild-type and mutant channels.Abstract The capacity to sense temperature is essential for the survival of all animals. At the molecular level, ion channels belonging to the transient receptor potential (TRP) family of channels function as temperature sensors in animals across several phyla. TRP channels are opened directly by changes in temperature and show pronounced sensitivity at their activation range. To determine how temperature activates these channels, we analysed channels belonging to the TRPA family, which detect heat in insects and cold in mammals. By constructing chimeric proteins consisting of human and Drosophila TRPA1 channels, we mapped regions that regulate thermal activation and identified residues in the pore helix that invert temperature sensitivity of TRPA1. From analysis of individual channels we defined the gating reaction of Drosophila TRPA1 and determined how mutagenesis alters the energy landscape for channel opening. Our results reveal specific molecular requirements for thermal activation of TRPA1 and provide mechanistic insight into this process.

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Previously, we reported photodynamic modification (PDM) of heterologous expressed HCN channels on membrane patches. In the presence of specific (FITC-cAMP) and non-specific (Rose Bengal) photosensitizers, light excitation transforms the function of HCN channels in an oxygen dependent manner. Here we extended the study to native HCN channels expressed in thalamocortical (TC) neurons in the Ventrobasal (VB) complex in the thalamus. We first discovered that blue light excitation significant increases the current amplitude and the rate of activation of the hyperpolarization-activated Ih current, which was a reversible process and did not require exogenous photosensitizers. However, when FITC-cAMP, but not FITC alone or FITC and cAMP, was loaded into the cell through whole-cell recording pipette, light excitation resulted in long-lasting increases in the voltage-insensitive, instantaneous Iinst component and correspondingly decreases in the Ih component. The Ih and Iinst after PDM can be blocked by Csþ and ZD7288, confirming the specific involvement of HCN channels. Next, we investigated the impacts of PDM of native HCN channels on the resting membrane potential (RMP) and input resistance (Rin) of VB neurons. As expected, after PDM, there was a significant positive shift in RMP. Importantly, both the long-lasting increase in Iinst and the positive shift in RMP after light excitation, but not the short-term and reversible increase in Ih during light excitation, could be blocked by Trolox-C, a widely used quencher for singlet oxygen. In summary, we report the PDM of native HCN channels under more physiological condition which should carry meanings for both basic researches and clinical treatments of diseases due to HCN channelopathy. BK potassium channels are attractive drug targets for a wide variety of human disorders affecting almost every organ system. However, the therapeutic potential of many BK channel modulators is limited by lack of tissue specificity, reflecting that the pore forming a-subunit (Slo1) is encoded by a single gene. Properties of modulators that can potentially enhance tissue specificity include (a) sensitivity to regulatory subunits that are expressed in a tissue-dependent manner and (b) state-dependent action, conferring sensitivity to tissue-specific differences in membrane voltage and Ca 2þ that activate BK channels. We have developed a novel 384-well fluorescent thallium-flux kinetic (FLIPR) assay to identify modulators with these properties. The screen includes assays on a panel of BK channel variants composed of hyperactive human Slo1 mutants (F380Y or R275C) in the presence or absence of different regulatory subunits (b1, b2, b2aFIW, b4, g1), expressed in U2OS cells with Bacmam virus. Hyperactive Slo1 mutants allow both inhibitors and activators to be reliably detected under resting cellular conditions. Comparison of R275C and F380Y identifies state-dependent modulators since the voltage-sensors of R275C are constitutively activated while F380Y are not. A test screen of small molecules and...

Ligand-gated ion channels (LGICs) are a group of diverse ion channels that are gated by ligands and play important roles in normal physiological and pathological conditions. Many of them are drug targets that have been pursued, are being pursued, and will likely be pursued in the future by pharmaceutical companies and academic groups for a variety of diseases. One of those LGICs is the GABA A receptor, a heterooligomeric chloride channel that can be blocked and modulated at various sites. In order to study the receptor's functional response to compounds, the manual patch-clamp method provides a detailed but lowthroughput electrophysiological characterization. QPatch II, a next-generation automated patch clamp machine that was recently developed by Sophion Bioscience, provides an automated electrophysiological study of ion channels. In this article, we use the GABA A receptor as an example for studying LGICs and describe two detailed protocols for using QPatch II to carry out pharmacological studies on the receptor.