Calcium activated chloride channel (CaCC) C
Unless otherwise stated all data on this page refer to the human proteins. Gene information is provided for human (Hs), mouse (Mm) and rat (Rn).
Overview
Chloride channels activated by intracellular calcium (CaCC) are widely expressed in excitable and non-excitable cells where they perform diverse functions [10]. The molecular nature of CaCC has been uncertain with both CLCA, TWEETY and BEST genes having been considered as likely candidates [7,11,14]. It is now accepted that CLCA expression products are unlikely to form channels per se and probably function as cell adhesion proteins, or are secreted [18]. Similarly, TWEETY gene products do not recapictulate the properties of endogenous CaCC. The bestrophins encoded by genes BEST1-4 have a topology more consistent with ion channels [11] and form chloride channels that are activated by physiological concentrations of Ca2+, but whether such activation is direct is not known [11]. However, currents generated by bestrophin over-expression do not resemble native CaCC currents. The evidence for and against bestrophin proteins forming CaCC is critically reviewed by Duran et al. [7]. Recently, a new gene family, TMEM16 (anoctamin) consisting of 10 members (TMEM16A-K; anoctamin 1-10) has been identified and there is firm evidence that some of these members form chloride channels [6,12]. TMEM16A (anoctamin 1; Ano 1) produces Ca2+-activated Cl- currents with kinetics similar to native CaCC currents recorded from different cell types [2,21-22,27]. Knockdown of TMEM16A greatly reduces currents mediated by calcium-activated chloride channels in submandibular gland cells [27] and smooth muscle cells from pulmonary artery [15]. In TMEM16A(-/-) mice secretion of Ca2+-dependent Cl- secretion by several epithelia is reduced [17,21]. Alternative splicing regulates the voltage- and Ca2+- dependence of TMEM16A and such processing may be tissue-specific manner and thus contribute to functional diversity [8]. There are also reports that TMEM16B (anoctamin 2; Ano 2) supports CaCC activity (e.g.[19]) and in TMEM16B(-/-) mice Ca-activated Cl- currents in the main olfactory epithelium (MOE) and in the vomeronasal organ are virtually absent [1].
Channels and Subunits
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How to cite this family page
Database page citation:
Calcium activated chloride channel (CaCC). Accessed on 19/04/2024. IUPHAR/BPS Guide to PHARMACOLOGY, http://www.guidetopharmacology.org/GRAC/FamilyDisplayForward?familyId=130.
Concise Guide to PHARMACOLOGY citation:
Alexander SPH, Mathie AA, Peters JA, Veale EL, Striessnig J, Kelly E, Armstrong JF, Faccenda E, Harding SD, Davies JA et al. (2023) The Concise Guide to PHARMACOLOGY 2023/24: Ion channels. Br J Pharmacol. 180 Suppl 2:S145-S222.
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Blockade of ICl(Ca) by niflumic acid, DIDS and 9-anthroic acid is voltage-dependent whereas block by NPPB is voltage-independent [10]. Extracellular niflumic acid; DCDPC and 9-anthroic acid (but not DIDS) exert a complex effect upon ICl(Ca) in vascular smooth muscle, enhancing and inhibiting inwardly and outwardly directed currents in a manner dependent upon [Ca2+]i (see [13] for summary). Considerable crossover in pharmacology with large conductance Ca2+-activated K+ channels also exists (see [9] for overview). Two novel compounds, CaCCinh-A01 and CaCCinh-B01 have been identified as blockers of calcium-activated chloride channels in T84 human intestinal epithelial cells [5]). Significantly, other novel compounds totally block currents mediated by TMEM116A, but have only a modest effect upon total current mediated by CaCC native to T84 cells or human bronchial epithelial cells, suggesting that TMEM16A is not the predominant CaCC in such cells [16]. CaMKII modulates CaCC in a tissue dependent manner (reviewed by [10,13]). CaMKII inhibitors block activation of ICl(Ca) in T84 cells but have no effect in parotid acinar cells. In tracheal and arterial smooth muscle cells, but not portal vein myocytes, inhibition of CaMKII reduces inactivation of ICl(Ca). Intracellular Ins(3,4,5,6)P4 may act as an endogenous negative regulator of CaCC channels activated by Ca2+, or CaMKII. Smooth muscle CaCC are also regulated positively by Ca2+-dependent phosphatase, calcineurin (see [13] for summary).