5b (novel blocker of ASICs) has little effect converse shoes on inward GABAergic currents in  HEPES 10' solution. In the same series of experiments during each sweep evoked PSCs were recorded below their reversal potential as inward currents ( a ), and above the reversal potential, as outward ones ( b ). Superimposed traces of original current traces (averages of 10 sequential PSCs) before (solid lines) and after (dotted lines) 5b (1 ¼M) application are shown on the right panel, summary graphs ( n = 5) are shown on the left panel. PSC-amplitudes were normalized to control values (average of 20 PSCs preceding drug application).

In spite of growing evidence indicating that the density of ASICs is substantially higher in GABAergic interneurons than in glutamatergic cells [ 17 ] and recent demonstration of functional crosstalk between ASICs and GABA A -receptors [ 10 , 11 ], the possible involvement of ASICs in the regulation converse cdg of GABAergic transmission remained unclear. In our work we present evidence for the first time that ASICs play a functional role at hippocampal GABAergic synapses. This role is mediated, at least partially, by a postsynaptic but (predominantly) modulatory mechanism.We found that GABAergic postsynaptic currents, recorded below their reversal potential as inward converse hi tops currents, are suppressed by all the employed blockers of ASICs.

In the same cells the suppression of postsynaptic currents, recorded above their reversal potential as outward currents was statistically insignificant.Apart from the chemical dissimilarity of amiloride and diminazene, they are structurally different [ 24 ], and mechanisms of their action on ASICs are different as well [ 24 ]. Similarly, amiloride and 5b have different mechanisms of action on ASICs [ 21 ]. Indeed, 5b is an orthosteric antagonist of ASIC1 [ 21 ] while amiloride is an open channel blocker [ 33 ].

Additionally, we would like to mention that although amioloride converse c d g is known to be not selective at high concentrations (for instance [ 34 ]), at concentration (25 ¼M) used in our experiments amiloride was shown to be a potent antagonist, mainly for ASIC receptors. As far as we know, diminazene is rather selective against ASICs within the time scale of our experiments (minutes). It does target DNA [ 35 ], but related consequences of this action shouldn't be expected within minutes. Indeed, we are not aware of any other than ASICs targets of diminazene, which could be responsible for  rapid' side effects.

Activation of GABA A -receptors strongly changed ASIC-currents amplitude and pharmacological sensitivity [ 10 ], and the effect was blocked by antagonists of GABA A receptors [ 10 ]. On the other hand, a modulatory effect of ASIC activation on GABA A -currents was also observed in HEK293 cells co-transfected with GABA A and ASIC1a or in primary cultured DRG neurons. The immunoassays showed that both GABA A and ASIC1a proteins were co-immunoprecipitated mutually either in HEK293 cells co-transfected with GABA A and ASIC1a or in primary cultured DRG neurons [ 11 ]. These data suggest direct protein-protein mechanism of interaction between GABA A and ASICs.

Indeed, this should be expected if the effect cdg converse of 5b on inward PSCS in the absence of bicuculline is due to crosstalk between ASICs and GABA A -receptors, because the crosstalk in isolated neurons was blocked by antagonists of GABA A -receptors- receptors bicuculline and picrotoxin [ 10 ].Within the framework of this assumption, differential effects of the ASICs antagonists on inward and outward PSCs which we observed in our experiments would indicate that this interaction is voltage-dependent. In this regard, possibility to alter GABA-currents decay by changing voltage [ 37 , 38 ] and activation of ASICs [ 11 ] may be not just a coincidence.