Calcium-dependent chloride current in rat cerebellar Purkinje cell membranes

Role of Potassium Ions in Regulation of Calcium-Activated Chloride Channels

Using the patch-clamp method in the whole cell configuration, it was shown that external potassium ions play an important role in the regulation of calcium-activated chloride channels (CaCCs). A clear dependence of the conductivity of the СаССs on the external potassium concentration was shown. The effect of external potassium in the range 0-15 mM on the conductivity of chloride channels was significantly greater than the effect it had on other ionic currents (sodium or potassium). There is reason to believe that these changes in the conductivity of CaCCs may contribute to the development of pathophysiological processes such as hypokalemia or hyperkalemia.

[Calcium-activated chloride channels: structure, properties, role in physiological and pathological processes]

Ca2+-activated chloride channels (CaCC) are a class of intracellular calcium activated chloride channels that mediate numerous physiological functions. In 2008, the molecular structure of CaCC was determined. CaCC are formed by the protein known as anoctamine 1 (ANO1 or TMEM16A). CaCC mediates the secretion of Cl- in secretory epithelia, such as the airways, salivary glands, intestines, renal tubules, and sweat glands. The presence of CaCC has also been recognized in the vascular muscles, smooth muscles of the respiratory tract, which control vascular tone and hypersensitivity of the respiratory tract. TMEM16A is activated in many cancers; it is believed that TMEM16A is involved in carcinogenesis. TMEM16A is also involved in cancer cells proliferation. The role of TMEM16A in the mechanisms of hypertension, asthma, cystic fibrosis, nociception, and dysfunction of the gastrointestinal tract has been determined. In addition to TMEM16A, its isoforms are involved in other physiological and pathophysiological processes. TMEM16B (or ANO2) is involved in the sense of smell, while ANO6 works like scramblase, and its mutation causes a rare bleeding disorder, known as Scott syndrome. ANO5 is associated with muscle and bone diseases. TMEM16A interacts with various cellular signaling pathways including: epidermal growth factor receptor (EGFR), mitogen-activated protein kinases (MAPK), calmodulin (CaM) kinases, transforming growth factor TGF-β. The review summarizes existing information on known natural and synthetic compounds that can block/modulate CaCC currents and their effect on some pathologies in which CaCC is involved.

Effect of New Derivatives of 2-Aminothiophene-3-Carboxylic Acid on Calcium-Activated Chloride Currents in Rat Neurons

Using the patch-clamp method in the whole-cell configuration, we showed that the new derivatives of 2-aminothiophene-3-carboxylic acid, which were synthesized by us earlier, can both block (compound 1) and potentiate (compound 2) calcium-activated chloride currents in single rat cerebellar Purkinje cells.

Key role of external chloride ions in regulation of fast sodium channels in rat cerebellum Purkinje neurons

A decrease in the external chloride ion concentration to 4 mM caused a decrease in the fast sodium current to 85-100% in rat cerebellum Purkinje neurons in the whole-cell configuration using the patchclamp method. This effect did not depend on the main cation from the internal side of the cell membrane (120 mM of potassium or cesium) and also appeared when Cl^- was substituted with sulfate (SO₂^-4) or phosphate (H₂PO₄^-) anion outside of the cell. The effect was reversible after washing out the low chloride by the standard saline.

Modification of Calcium-Activated Chloride Currents in Cerebellar Purkinje Neurons

The whole-cell voltage clamp technique was employed to record the total ionic currents in rat cerebellar Purkinje neurons. When intrapipette solution contained 120 mM KCl, replacement of the standard external physiological saline with Na-free solution resulted in appearance of inward tail current after the end of the depolarizing pulse. When intrapipette potassium ions were replaced for cesium ones, the tail currents were observed even in the presence of normal Na⁺ concentration (140 mM) in the external solution. Tail currents were not observed when external solution contained no Cl^- and/or Ca²⁺ ions. Niflumic acid (25-100 μM) blocked these currents by 80-100%. Complete replacement of external Na⁺ for Tris ions pronouncedly augmented the amplitude and duration of the tail currents. These findings suggest that the tail transients in rat cerebellar Purkinje neurons are calcium-activated chloride currents whose amplitude and kinetics depend on ionic composition of the extracellular and intracellular solutions.

Tetraethylammonium and 4-aminopyridine block calcium-dependent chloride current in rat cerebellum Purkinje cells

Using patch-clamp method (whole cell configuration), it was shown that tetraethylammonium (TEA) and 4-aminopyridine (4-AP) block calcium-dependent chloride currents in the membrane of freshly isolated cerebellar Purkinje cells of rats (12-15 days). In the concentration range studied (50 μM-10 mM TEA and 100 μM-1 mM 4-AP), both compounds blocked the chloride current at IC₅₀ 130 μM for TEA and 110 μM for 4-AP. TEA blockade was reversible after washing. The effect of 4-AP at concentrations greater than 100 μM was irreversible: both outward and inward chloride currents were blocked even after the removal of 4-AP from the incubation medium.