Ausgrabungen » converse white

ÿþAs mentioned above, ASIC inhibition is currently not used clinically. The converse white present compounds except for amiloride, which is clinically used as ENaC inhibitor (IC 50 = 100 200 nM), have been characterized in cell systems and in part also in animal models. An interesting recent review of ASIC pharmacology is provided by Baron and Lingueglia ( 2015 ). Amiloride has a low potency (EC 50 of 10 100 ¼M) and selectivity on ASIC peak currents and does not inhibit the sustained ASIC currents. Amiloride binds into the pore of ENaC and ASICs (Schild et al.1997 ; Adams et al.1999 ; Alijevic and Kellenberger, 2012 ).

The site of action of other small molecule inhibitors on ASICs is not known. Amiloride derivatives modified at the five position of the pyrazine ring by hydrophobic groups increased the potency for ASIC3 inhibition by up to 100 fold (Kuduk et al.2009 ). Nafamostat mesylate, an converse black anti inflammatory agent and protease inhibitor, contains a guanidinium moiety as do amiloride and GMQ and was shown to inhibit ASIC currents, including the sustained current of ASIC3, with IC 50 values of 2 70 ¼M (Ugawa et al.2007 ). The chemically unrelated compound A 317 567 inhibits peak and sustained converse high tops currents of neuronal and recombinant ASICs with IC 50 values between 2 and 30 ¼M (Dube et al.2005 ).

Some of them have a high affinity for selected targets (IC 50 of PcTx1 for ASIC1a: 0.4 13 nM, EC 50 of Mit toxin for ASIC1a: 9 nM; Baron et al.2013 ) and may be used in binding studies after labelling, as shown for PcTx1 (Salinas et al.2006 ). The ASIC toxins have so far not been shown to target other channels besides ASICs, with the exception of APETx2, which also inhibits some voltage gated Na channel isoforms (IC 50 in the converse black high tops range of nanomolar to low micromolar concentrations) (Blanchard et al.2012 ; Peigneur et al.2012 ).

PcTx1 inhibits mammalian ASIC1a by an alkaline shift in the pH dependence of steady state desensitization (leading to complete desensitization at pH 7.4), while Mambalgin inhibition is due to an acidic shift in the pH dependence of activation. The mechanisms of action of the other ASIC toxins are currently not known. Co crystallization showed that PcTx1 binds to the acidic pocket of ASIC1 and that the much larger Mit toxin binds to the wrist, palm and thumb domains, without however reaching into the acidic pocket (Baconguis and Gouaux, 2012 ; Dawson et al.2012 ; Baconguis et al.2014 ). Site directed mutagenesis indicated that Mambalgins also bind to the acidic pocket (Salinas et al.2014 ; Schroeder et al.2014 ).

ASICs in contrast are activated by extracellular acidification. Administration of specific ASIC1a antagonists or disruption of the ASIC1a gene eliminates the majority of the acid induced currents in CNS neurons (Wemmie et al.2013 ; Wu et al.2013 ). This demonstrates that the ASIC1a homomers and ASIC1a containing heteromers are the principal sensors of rapid extracellular acidification in the brain. ASIC1a,  2a and  2b converse trainers are widely expressed in the CNS (reiewed in Wemmie et al.2013 ; Kellenberger and Schild, 2015 ).

Localization by immunohistochemistry studies, evidence for the interaction with the postsynaptic proteins PICK1 and AKAP150, and co localization with PSD 95 in spines together indicate that ASIC1a has a somatodendritic distribution (Zha, 2013 ) and is well situated for the detection of rapid synaptic pH changes. Several recent studies expressed light activated proton pumps in neurons or astrocytes. Light induced activation of these pumps led to extracellular acidification and ASIC activation (Li et al.2014 ; Zeng et al.2015 ; Ferenczi et al.2016 ).