Acid Sensing Ion Channels (ASICs) in NS20Y cells - potential role in neuronal differentiation.

Cultured neuronal cell lines can express properties of mature neurons if properly differentiated. Although the precise mechanisms underlying neuronal differentiation are not fully understood, the expression and activation of ion channels, particularly those of Ca(2+)-permeable channels, have been suggested to play a role. In this study, we explored the presence and characterized the properties of acid-sensing ion channels (ASICs) in NS20Y cells, a neuronal cell line previously used for the study of neuronal differentiation. In addition, the potential role of ASICs in cell differentiation was explored. Reverse Transcription Polymerase Chain Reaction and Western blot revealed the presence of ASIC1 subunits in these cells. Fast drops of extracellular pH activated transient inward currents which were blocked, in a dose dependent manner, by amiloride, a non-selective ASIC blocker, and by Psalmotoxin-1 (PcTX1), a specific inhibitor for homomeric ASIC1a and heteromeric ASIC1a/2b channels. Incubation of cells with PcTX1 significantly reduced the differentiation of NS20Y cells induced by cpt-cAMP, as evidenced by decreased neurite length, dendritic complexity, decreased expression of functional voltage gated Na(+) channels. Consistent with ASIC1a inhibition, ASIC1a knockdown with small interference RNA significantly attenuates cpt-cAMP-induced increase of neurite outgrowth. In summary, we described the presence of functional ASICs in NS20Y cells and demonstrate that ASIC1a plays a role in the differentiation of these cells.

Regulating Factors in Acid-Sensing Ion Channel 1a Function.

In recent years, research of acid sensing ion channels (ASICs) has increased tremendously, especially studies focusing on ASIC1a, which plays a critical role in many important physiologic and pathological functions. This review will discuss factors regulating ASIC1a expression and activity in various conditions and will provide a theoretical basis for clinical development and application of ASIC1a modifiers.

Zinc-permeable ion channels: effects on intracellular zinc dynamics and potential physiological/pathophysiological significance.

Zinc (Zn(2+)) is one of the most important trace metals in the body. It is necessary for the normal function of a large number of protein s including enzymes and transcription factors. While extracellular fluid may contain up to micromolar Zn(2+), intracellular Zn(2+) concentration is generally maintained at a subnanomolar level; this steep gradient across the cell membrane is primarily attributable to Zn(2+) extrusion by Zn(2+) transporting systems. Interestingly, systematic investigation has revealed that activities, previously believed to be dependent on calcium (Ca(2+)), may be partially mediated by Zn(2+). This is also supported by new findings that some Ca(2+)-permeable channels such as voltage-dependent calcium channels (VDCCs), N-methyl-D-aspartate receptors (NMDA), and amino-3- hydroxy-5-methyl-4-isoxazolepropionate receptors (AMPA-Rs) are also permeable to Zn(2+). Thus, the importance of Zn(2+) in physiological and pathophysiological processes is now more widely appreciated. In this review, we describe Zn(2+)- permeable membrane molecules, especially Zn(2+)-permeable ion channels, in intracellular Zn(2+)dynamics and Zn(2+) mediated physiology/pathophysiology.

Local anesthetic lidocaine inhibits TRPM7 current and TRPM7-mediated zinc toxicity.

BACKGROUND: Previous study demonstrated that overstimulation of TRPM7 substantially contributes to zinc-mediated neuronal toxicity. Inhibition of TRPM7 activity and TRPM7-mediated intracellular Zn(2+) accumulation may represent a promising strategy in the treatment of stroke. AIMS: To investigate whether local anesthetics lidocaine could inhibit TRPM7 channel and TRPM7-mediated zinc toxicity. METHODS: Whole-cell patch-clamp technique was used to investigate the effect of local anesthetics on TRPM7 currents in cultured mouse cortical neurons and TRPM7-overexpressed HEK293 cells. Fluorescent Zn(2+) imaging technique was used to study the effect of lidocaine on TRPM7-mediated intracellular Zn(2+) accumulation. TRPM7-mediated zinc toxicity in neurons was used to evaluate the neuroprotective effect of lidocaine. RESULTS: (1) Lidocaine dose dependently inhibits TRPM7-like currents, with an IC50 of 11.55 and 11.06 mM in cultured mouse cortical neurons and TRPM7-overexpressed HEK293 cells, respectively; (2) Lidocaine inhibits TRPM7 currents in a use/frequency-dependent manner; (3) Lidocaine inhibits TRPM7-mediated intracellular Zn(2+) accumulation in both cortical neurons and TRPM7-overexpressed HEK293 cells; (4) TRPM7-mediated Zn(2+) toxicity is ameliorated by lidocaine in cortical neurons; (5) QX-314 has a similar inhibitory effect as lidocaine on TRPM7 currents when applied extracellularly; (6) Procaine also shows potent inhibitory effect on the TRPM7 currents in cortical neurons. CONCLUSION: Our data provide the first evidence that local anesthetic lidocaine inhibits TRPM7 channel and TRPM7-mediated zinc toxicity.

Translational strategies for neuroprotection in ischemic stroke--focusing on acid-sensing ion channel 1a.

Ischemic stroke contributes to the majority of brain injuries and remains to be a leading cause of death and long-term disability. Despite the devastating pathology and high incidence of disease, there remain only few treatment options (TPA and endovascular procedures), which may be hampered by time-dependent administration among a variety of other factors. Promising research of glutamate receptor antagonists has been unsuccessful in clinical trial. But, the mechanism by which glutamate receptors initiate injury by excessive calcium overload has spurred investigation of new and potentially successful candidates for stroke therapy. Acid-sensing ion channels (ASICs) may contribute to poor stroke prognosis due to localized drop in brain pH, resulting in excessive calcium overload, independent of glutamate activation. Accumulating studies targeting ASICs have underscored the importance of understanding inhibition, regulation, desensitization, and trafficking of this channel and its role in disease. This review will discuss potential directions in translational ASIC research for future stroke therapies.