ATP release via anion channels

ATP serves not only as an energy source for all cell types but as an ‘extracellular messenger-for autocrine and paracrine signalling. It is released from the cell via several different purinergic signal efflux pathways. ATP and its Mg2+ and/or H+ salts exist in anionic forms at physiological pH and may exit cells via some anion channel if the pore physically permits this. In this review we survey experimental data providing evidence for and against the release of ATP through anion channels. CFTR has long been considered a probable pathway for ATP release in airway epithelium and other types of cells expressing this protein, although non-CFTR ATP currents have also been observed. Volume-sensitive outwardly rectifying (VSOR) chloride channels are found in virtually all cell types and can physically accommodate or even permeate ATP4- in certain experimental conditions. However, pharmacological studies are controversial and argue against the actual involvement of the VSOR channel in significant release of ATP. A large-conductance anion channel whose open probability exhibits a bell-shaped voltage dependence is also ubiquitously expressed and represents a putative pathway for ATP release. This channel, called a maxi-anion channel, has a wide nanoscopic pore suitable for nucleotide transport and possesses an ATP-binding site in the middle of the pore lumen to facilitate the passage of the nucleotide. The maxi-anion channel conducts ATP and displays a pharmacological profile similar to that of ATP release in response to osmotic, ischemic, hypoxic and salt stresses. The relation of some other channels and transporters to the regulated release of ATP is also discussed

Chondrocyte channel transcriptomics: do microarray data fit with expression and functional data?

To date, a range of ion channels have been identified in chondrocytes using a number of different techniques, predominantly electrophysiological and/or biomolecular; each of these has its advantages and disadvantages. Here we aim to compare and contrast the data available from biophysical and microarray experiments. This letter analyses recent transcriptomics datasets from chondrocytes, accessible from the European Bioinformatics Institute (EBI). We discuss whether such bioinformatic analysis of microarray datasets can potentially accelerate identification and discovery of ion channels in chondrocytes. The ion channels which appear most frequently across these microarray datasets are discussed, along with their possible functions. We discuss whether functional or protein data exist which support the microarray data. A microarray experiment comparing gene expression in osteoarthritis and healthy cartilage is also discussed and we verify the differential expression of 2 of these genes, namely the genes encoding the BK and aquaporin channels

Rare CACNA1A mutations leading to congenital ataxia

Human mutations in the CACNA1A gene that encodes the pore-forming α1A subunit of the voltage-gated CaV2.1 (P/Q-type) Ca2+ channel cause multiple neurological disorders including sporadic and familial hemiplegic migraine, as well as cerebellar pathologies such as episodic ataxia, progressive ataxia, and early-onset cerebellar syndrome consistent with the definition of congenital ataxia (CA), with presentation before the age of 2 years. Such a pathological role is in accordance with the physiological relevance of CaV2.1 in neuronal tissue, especially in the cerebellum. This review deals with the report of the main clinical features defining CA, along with the presentation of an increasing number of CACNA1A genetic variants linked to this severe cerebellar disorder in the context of Ca2+ homeostasis alteration. Moreover, the review describes each pathological mutation according to structural location and known molecular and cellular functional effects in both heterologous expression systems and animal models. In view of this information in correlation with the clinical phenotype, we take into consideration different pathomechanisms underlying the observed motor dysfunction in CA patients carrying CACNA1A mutations. Present therapeutic management in CA and options for the development of future personalized treatment based on CaV2.1 dysfunction are also discussed.This work was funded by the Spanish Ministry of Science and Innovation, the State Research Agency (AEI, Agencia Estatal de Investigación), and FEDER Funds (Fondo Europeo de Desarrollo Regional): Grants RTI2018-094809-B-I00 to J.M.F.F. and CEX2018-000792-M through the “María de Maeztu” Programme for Units of Excellence in R&D to “Departament de Ciències Experimentals i de la Salut”. M.S. is supported by the Generalitat de Catalunya (PERIS SLT008/18/00194) and National Grant PI17/00101 from the National R&D&I Plan, cofinanced by the Instituto de Salud Carlos III (Subdirectorate-General for Evaluation and Promotion of Health Research) and European Regional Development Fund. M.I.-S. holds a “Juan de la Cierva-Incorporación” Fellowship funded by the Spanish Ministry of Science and Innovation

ATP release from non-excitable cells

All cells release nucleotides and are in one way or another involved in local autocrine and paracrine regulation of organ function via stimulation of purinergic receptors. Significant technical advances have been made in recent years to quantify more precisely resting and stimulated adenosine triphosphate (ATP) concentrations in close proximity to the plasma membrane. These technical advances are reviewed here. However, the mechanisms by which cells release ATP continue to be enigmatic. The current state of knowledge on different suggested mechanisms is also reviewed. Current evidence suggests that two separate regulated modes of ATP release co-exist in non-excitable cells: (1) a conductive pore which in several systems has been found to be the channel pannexin 1 and (2) vesicular release. Modes of stimulation of ATP release are reviewed and indicate that both subtle mechanical stimulation and agonist-triggered release play pivotal roles. The mechano-sensor for ATP release is not yet defined