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Molecular Mechanisms of Activation and Regulation of ANO1-Encoded Ca2+-Activated Cl- Channels.
Ca2+-activated Cl- channels (CaCCs) perform a multitude of functions including the control of cell excitability, regulation of cell volume and ionic homeostasis, exocrine and endocrine secretion, fertilization, amplification of olfactory sensory function, and control of smooth muscle cell contractility. CaCCs are the translated products of two members (ANO1 and ANO2, also known as TMEM16A and TMEM16B) of the Anoctamin family of genes comprising ten paralogs. This review focuses on recent progress in understanding the molecular mechanisms involved in the regulation of ANO1 by cytoplasmic Ca2+, post-translational modifications, and how the channel protein interacts with membrane lipids and protein partners. After first reviewing the basic properties of native CaCCs, we then present a brief historical perspective highlighting controversies about their molecular identity in native cells. This is followed by a summary of the fundamental biophysical and structural properties of ANO1. We specifically address whether the channel is directly activated by internal Ca2+ or indirectly through the intervention of the Ca2+-binding protein Calmodulin (CaM), and the structural domains responsible for Ca2+- and voltage-dependent gating. We then review the regulation of ANO1 by internal ATP, Calmodulin-dependent protein kinase II-(CaMKII)-mediated phosphorylation and phosphatase activity, membrane lipids such as the phospholipid phosphatidyl-(4,5)-bisphosphate (PIP2), free fatty acids and cholesterol, and the cytoskeleton. The article ends with a survey of physical and functional interactions of ANO1 with other membrane proteins such as CLCA1/2, inositol trisphosphate and ryanodine receptors in the endoplasmic reticulum, several members of the TRP channel family, and the ancillary Ξ+ channel Ξ² subunits KCNE1/5
Anion-Sensitive Regions of L-Type CaV1.2 Calcium Channels Expressed in HEK293 Cells
L-type calcium currents (ICa) are influenced by changes in extracellular chloride, but sites of anion effects have not been identified. Our experiments showed that CaV1.2 currents expressed in HEK293 cells are strongly inhibited by replacing extracellular chloride with gluconate or perchlorate. Variance-mean analysis of ICa and cell-attached patch single channel recordings indicate that gluconate-induced inhibition is due to intracellular anion effects on Ca2+ channel open probability, not conductance. Inhibition of CaV1.2 currents produced by replacing chloride with gluconate was reduced from βΌ75%β80% to βΌ50% by omitting Ξ² subunits but unaffected by omitting Ξ±2Ξ΄ subunits. Similarly, gluconate inhibition was reduced to βΌ50% by deleting an Ξ±1 subunit N-terminal region of 15 residues critical for Ξ² subunit interactions regulating open probability. Omitting Ξ² subunits with this mutant Ξ±1 subunit did not further diminish inhibition. Gluconate inhibition was unchanged with expression of different Ξ² subunits. Truncating the C terminus at AA1665 reduced gluconate inhibition from βΌ75%β80% to βΌ50% whereas truncating it at AA1700 had no effect. Neutralizing arginines at AA1696 and 1697 by replacement with glutamines reduced gluconate inhibition to βΌ60% indicating these residues are particularly important for anion effects. Expressing CaV1.2 channels that lacked both N and C termini reduced gluconate inhibition to βΌ25% consistent with additive interactions between the two tail regions. Our results suggest that modest changes in intracellular anion concentration can produce significant effects on CaV1.2 currents mediated by changes in channel open probability involving Ξ² subunit interactions with the N terminus and a short C terminal region
INtegration of DEPression Treatment into HIV Care in Uganda (INDEPTH-Uganda): study protocol for a randomized controlled trial
Recurrent exophytic growth on maxillary posterior edentulous alveolar ridge β a diagnostic challenge
Giant Hypervascular Lesion of the Sinonasal Tract Invading the Anterior Skull Base and Orbit: A Puzzling Case
Pyogenic granuloma of the oral cavity: Comparative study of its clinicopathological and immunohistochemical features
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