Function and Regulation of the Calcium-Activated Chloride Channel Anoctamin 1 (TMEM16A)

Various human tissues express the calcium-activated chloride channel Anoctamin 1 (ANO1), also known as TMEM16A. ANO1 allows the passive chloride flux that controls different physiological functions ranging from muscle contraction, fluid and hormone secretion, gastrointestinal motility, and electrical excitability. Overexpression of ANO1 is associated with pathological conditions such as hypertension and cancer. The molecular cloning of ANO1 has led to a surge in structural, functional, and physiological studies of the channel in several tissues. ANO1 is a homodimer channel harboring two pores - one in each monomer - that work independently. Each pore is activated by voltage-dependent binding of two intracellular calcium ions to a high-affinity-binding site. In addition, the binding of phosphatidylinositol 4,5-bisphosphate to sites scattered throughout the cytosolic side of the protein aids the calcium activation process. Furthermore, many pharmacological studies have established ANO1 as a target of promising compounds that could treat several illnesses. This chapter describes our current understanding of the physiological roles of ANO1 and its regulation under physiological conditions as well as new pharmacological compounds with potential therapeutic applications.

Metabolic acidosis and hyperkalemia differentially regulate cation HCN3 channel in the rat nephron

The kidney controls body fluids, electrolyte and acid-base balance. Previously, we demonstrated that hyperpolarization-activated and cyclic nucleotide-gated (HCN) cation channels participate in ammonium excretion in the rat kidney. Since acid-base balance is closely linked to potassium metabolism, in the present work we aim to determine the effect of chronic metabolic acidosis (CMA) and hyperkalemia (HK) on protein abundance and localization of HCN3 in the rat kidney. CMA increased HCN3 protein level only in the outer medulla (2.74 ± 0.31) according to immunoblot analysis. However, immunofluorescence assays showed that HCN3 augmented in cortical proximal tubules (1.45 ± 0.11) and medullary thick ascending limb of Henle's loop (4.48 ± 0.45) from the inner stripe of outer medulla. HCN3 was detected in brush border membranes (BBM) and mitochondria of the proximal tubule by immunogold electron and confocal microscopy in control conditions. Acidosis did not alter HCN3 levels in BBM and mitochondria but augmented them in lysosomes. HCN3 was also immuno-detected in mitoautophagosomes. In the distal nephron, HCN3 was expressed in principal and intercalated cells from cortical to medullary collecting ducts. CMA did not change HCN3 abundance in these nephron segments. In contrast, HK doubled HCN3 level in cortical collecting ducts and favored its basolateral localization in principal cells from the inner medullary collecting ducts. These findings further support HCN channels contribution to renal acid-base and potassium balance.

Novel Potassium Channels in Kidney Mitochondria: The Hyperpolarization-Activated and Cyclic Nucleotide-Gated HCN Channels

Hyperpolarization-activated cationic HCN channels comprise four members (HCN1–4) that control dendritic integration, synaptic transmission and action potential firing. In the kidney, HCN1, HCN2 and HCN3 are differentially expressed and contribute to the transport of sodium, potassium (K⁺) and ammonium into the nephrons. HCN3 is regulated by K⁺ diets in the kidney. In this work we performed a proteomic analysis of HCN3 expressed in human embryonic kidney cells (HEK293 cells). More than 50% of the interacting proteins belonged to mitochondria. Therefore, we explored the presence of HCN channels in kidney mitochondria. By immunoblotting and immunogold electron microscopy HCN3 protein expression was found in rat kidney mitochondria; it was also confirmed in human kidney. Patch-clamp recordings of renal mitochondria and mitochondria from HEK293 cells overexpressing HCN1, HCN2 and HCN3 channels, stained with MitoTracker Green FM, indicated that only HCN3 could produce inwardly K⁺ currents that were inhibited by ZD7288, a specific blocker of HCN channels. Furthermore, ZD7288 caused inhibition of the oxygen consumption coupled to ATP synthesis and hyperpolarization of the inner mitochondrial membrane. In conclusion, we show for the first time that pacemaker HCN channels contribute to K⁺ transport in mitochondria facilitating the activity of the respiratory chain and ATP synthesis by controlling the inner mitochondrial membrane potential.

Aged garlic extract delays the appearance of infarct area in a cerebral ischemia model, an effect likely conditioned by the cellular antioxidant systems

Experimental evidence has shown that some garlic-derived products have a protective effect against ischemic brain injury. The present study was designed to investigate the effect of aged garlic extract (AGE), establish the therapeutic window, and determine its protective mechanism in a cerebral ischemia model. Animals were subjected to middle cerebral artery occlusion (MCAO) for 2h and treated with 1.2ml/kg body wt.(i.p.) of AGE 30min before, at the beginning of (0R), or 1h after reperfusion. The 0R treatment significantly reduced the size of the infarct area after 2h of reperfusion. Repeated doses subsequent to the 0R treatment (at 1, 2, or 3h after reperfusion) had no effect on the temporal window of protection. The protective 0R treatment with AGE prevented the increase in nitrotyrosine and the decrease in total superoxide dismutase, glutathione peroxidase, and extracellular superoxide dismutase activities induced by MCAO. These data indicate that AGE delays the effects of ischemia/reperfusion-induced neuronal injury. However, this treatment itself was not associated with a noticeable improvement in the neurological outcome, or with an effect on the inflammatory response. We conclude that the neuroprotective effect of AGE in the 0R treatment might be associated with control of the free-radical burst induced by reperfusion, preservation of antioxidant enzyme activity, and the delay of other pathophysiological processes.