Membranes in cells have defined distributions of lipids in each leaflet, controlled by lipid scramblases and flip/floppases. However, for some intracellular membranes such as the endoplasmic reticulum (ER) the scramblases have not been identified. Members of the TMEM16 family have either lipid scramblase or chloride channel activity. Although TMEM16K is widely distributed and associated with the neurological disorder autosomal recessive spinocerebellar ataxia type 10 (SCAR10), its location in cells, function and structure are largely uncharacterised. Here we show that TMEM16K is an ER-resident lipid scramblase with a requirement for short chain lipids and calcium for robust activity. Crystal structures of TMEM16K show a scramblase fold, with an open lipid transporting groove. Additional cryo-EM structures reveal extensive conformational changes from the cytoplasmic to the ER side of the membrane, giving a state with a closed lipid permeation pathway. Molecular dynamics simulations showed that the open-groove conformation is necessary for scramblase activity.

Pericyte-mediated capillary constriction decreases cerebral blood flow in stroke after an occluded artery is unblocked. The determinants of pericyte tone are poorly understood. We show that a small rise in cytoplasmic Ca²⁺ concentration ([Ca²⁺]_i) in pericytes activated chloride efflux through the Ca²⁺-gated anion channel TMEM16A, thus depolarizing the cell and opening voltage-gated calcium channels. This mechanism strongly amplified the pericyte [Ca²⁺]_i rise and capillary constriction evoked by contractile agonists and ischemia. In a rodent stroke model, TMEM16A inhibition slowed the ischemia-evoked pericyte [Ca²⁺]_i rise, capillary constriction, and pericyte death; reduced neutrophil stalling; and improved cerebrovascular reperfusion. Genetic analysis implicated altered TMEM16A expression in poor patient recovery from ischemic stroke. Thus, pericyte TMEM16A is a crucial regulator of cerebral capillary function and a potential therapeutic target for stroke and possibly other disorders of impaired microvascular flow, such as Alzheimer’s disease and vascular dementia.

The Concise Guide to Pharmacology 2025/26 marks the seventh edition in this series of biennial publications in the British Journal of Pharmacology. Presented in landscape format, the guide provides a comparative overview of the pharmacology of drug target families. The concise nature of the Concise Guide refers to the style of presentation, being clear, accessible, and well‐structured, rather than the scope of the content, which spans approximately 500 pages. The Concise Guide summarises the key pharmacological properties of around 1900 human drug targets, and nearly 7000 interactions, involving around 4400 ligands. While the content is a substantially condensed version of the more detailed information and links available at the www.guidetopharmacology.org website, the printed guide serves as a permanent, citable, point‐in‐time record, that remains stable despite ongoing updates to the online database. The full contents of this publication can be found at https://bpspubs.onlinelibrary.wiley.com/doi/10.1111/bph.70231 . The Concise Guides provide expert‐curated recommendations of ‘Gold Standard’ selective pharmacological tools, available either commercially or as donations, which enable the identification of individual drug targets or families of drug targets. While the Concise Guide offers a more streamlined overview, more comprehensive information, including detailed pharmacological profiles and links to multiple online databases, is available through the Guide to Pharmacology website. The 2025/26 edition of the Concise Guide is based on material current as of mid‐2025, and supersedes all previous editions, including the 2023/24 Guide, and earlier Guides to Receptors and Channels. It is produced in close conjunction with the Nomenclature and Standards Committee of the International Union of Basic and Clinical Pharmacology (NC‐IUPHAR), and as such provides official IUPHAR classification and nomenclature for human drug targets, where applicable. Ion channels are one of the six major pharmacological targets into which the Guide is divided, with the others being: G protein‐coupled receptors, nuclear hormone receptors, catalytic receptors, enzymes and transporters. Each section includes nomenclature guidance, concise summaries, information of the best available pharmacological tools, key references, and suggestions for further reading.

Background and Purpose: Ca²⁺‐activated Cl⁻ channels (CaCCs) are gated open by a rise in intracellular Ca²⁺ concentration ([Ca²⁺]_i), typically provoked by activation of G_q‐protein coupled receptors (G_qPCR). G_qPCR activation initiates depletion of plasmalemmal phosphatidylinositol 4,5‐bisphosphate (PIP₂). Here, we determined whether PIP₂ acts as a signalling lipid for CaCCs coded by the TMEM16A and TMEM16B genes.Experimental Approach: Patch‐clamp electrophysiology, in conjunction with genetically encoded systems to control cellular PIP₂ content, was used to define the mechanism of action of PIP₂ on TMEM16A and TMEM16B channels.Key Results: A water‐soluble PIP₂ analogue (diC8‐PIP₂) activated TMEM16A channels by up to fivefold and inhibited TMEM16B by ~0.2‐fold. The effects of diC8‐PIP₂ on TMEM16A currents were especially pronounced at low [Ca²⁺]_i. In contrast, diC8‐PIP₂ modulation of TMEM16B channels did not vary over a broad [Ca²⁺]_i range but was only detectable at highly depolarized membrane potentials. Modulation of TMEM16A and TMEM16B currents was due to changes in channel gating, while single channel conductance was unaltered. Co‐expression of TMEM16A or TMEM16B with a Danio rerio voltage‐sensitive phosphatase (DrVSP), which degrades PIP₂, led to reduction and enhancement of TMEM16A and TMEM16B currents respectively. These effects were abolished by an inactivating mutation in DrVSP and antagonized by simultaneous co‐expression of a phosphatidylinositol‐4‐phosphate 5‐kinase that catalyses PIP₂ formation.Conclusions and Implications: PIP₂ acts as a modifier of TMEM16A and TMEM16B channel gating. Drugs interacting with PIP₂ signalling may affect TMEM16A and TMEM16B channel gating and have potential uses in basic science and implications for therapy.

Key points: The recently identified TMEM16/anoctamin protein family includes Ca²⁺‐activated Cl⁻ channels (TMEM16A and TMEM16B), a Ca²⁺‐activated non‐selective cation channel (TMEM16F) and proteins for which the function remains unclear. TMEM16 channel proteins consist of eight putative transmembrane domains (TMs) with the 5th and 6th TMs flanking a loop predicted to protrude deep into the membrane. Recent studies suggest that this re‐entrant loop may compose part of the pore of TMEM16A channels while also containing residues involved in Ca²⁺ binding. Here, we investigate the functional role of the putative pore‐loop by examining the electrophysiological properties of chimeras produced by transplanting this region between TMEM16 family members with different conduction properties and Ca²⁺ sensitivities. We revealed that the putative pore‐loop of TMEM16 channels has an unexpected role in controlling the whole‐cell Ca²⁺‐activated Cl⁻ conductance by regulating the number of functional channels present on the plasma membrane. Abstract  The recently identified TMEM16/anoctamin protein family includes Ca²⁺‐activated anion channels (TMEM16A, TMEM16B), a cation channel (TMEM16F) and proteins with unclear function. TMEM16 channels consist of eight putative transmembrane domains (TMs) with TM5–TM6 flanking a re‐entrant loop thought to form the pore. In TMEM16A this region has also been suggested to contain residues involved in Ca²⁺ binding. The role of the putative pore‐loop of TMEM16 channels was investigated using a chimeric approach. Heterologous expression of either TMEM16A or TMEM16B resulted in whole‐cell anion currents with very similar conduction properties but distinct kinetics and degrees of sensitivity to Ca²⁺. Furthermore, whole‐cell currents mediated by TMEM16A channels were ∼six times larger than TMEM16B‐mediated currents. Replacement of the putative pore‐loop of TMEM16A with that of TMEM16B (TMEM16A‐B channels) reduced the currents by ∼six‐fold, while the opposite modification (TMEM16B‐A channels) produced a ∼six‐fold increase in the currents. Unexpectedly, these changes were not secondary to variations in channel gating by Ca²⁺ or voltage, nor were they due to changes in single‐channel conductance. Instead, they depended on the number of functional channels present on the plasma membrane. Generation of additional, smaller chimeras within the putative pore‐loop of TMEM16A and TMEM16B led to the identification of a region containing a non‐canonical trafficking motif. Chimeras composed of the putative pore‐loop of TMEM16F transplanted into the TMEM16A protein scaffold did not conduct anions or cations. These data suggest that the putative pore‐loop does not form a complete, transferable pore domain. Furthermore, our data reveal an unexpected role for the putative pore‐loop of TMEM16A and TMEM16B channels in the control of the whole‐cell Ca²⁺‐activated Cl⁻ conductance.