Inhibitory effects of amiloride on the current mediated by native GABA_A receptors in cultured neurons of rat inferior colliculus

Abstract

1. The diuretic amiloride is known to modulate the activity of several types of ion channels and membrane receptors in addition to its inhibitory effects on many ion transport systems. However, the effects of amiloride on some important ion channels and receptors, such as GABA(A) receptors, in the central nervous system have not been characterized. 2. In the present study, we investigated the functional action of amiloride on native GABA(A) receptors in cultured neurons of rat inferior colliculus using whole-cell patch-clamp recordings. 3. Amiloride reversibly inhibited the amplitude of the GABA-induced current (I(GABA)) in a concentration-dependent manner (IC(50) 454 +/- 24 micromol/L) under conditions of voltage-clamp with a holding potential at -60 mV. The inhibition depended on drug application mode and was independent of membrane potential. Amiloride did not change the reversal potential of I(GABA). Moreover, amiloride induced a parallel right-ward shift in the concentration-response curve for I(GABA) without altering the maximal value and Hill coefficient. 4. The present study shows that amiloride competitively inhibits the current mediated by native GABA(A) receptors in the brain region, probably via a direct action on GABA-binding sites on the receptor. The findings suggest that the functional actions of amiloride on GABA(A) receptors may result in possible side-effects on the central nervous system in the case of direct application of this drug into the cerebrospinal fluid for treatment of diseases such as brain tumours.

Acid extrusion via blood–brain barrier causes brain alkalosis and seizures after neonatal asphyxia

“…3B). We repeated the behavioural tests with the Na/H exchange inhibitor amiloride, because amiloride penetration across the blood–brain barrier is known to be poor (Sipos and Brem, 2000; Fisher, 2002; Liu et al , 2010). Notably, the effects of amiloride and MIA were similar (Fig.…”

“…This conclusion is based on (i) the post-asphyxia increase and alkaline overshoot of both brain intracellular pH and extracellular pH, which indicates a net loss of acid equivalents from brain tissue; (ii) direct measurements of the extracellular pH levels and dynamics in the brain and the rest of the body, which indicated a strict compartmentalization of brain extracellular pH by the blood–brain barrier under normal conditions and in response to asphyxia in the Day 6 rats; (iii) the specific block of the post-asphyxia brain alkalosis by MIA, an inhibitor of Na/H exchange (Kendall et al , 2006; Pedersen et al , 2006) and (iv) the equally strong inhibitory action on seizures by MIA and amiloride, whereof the latter is an Na/H exchange inhibitor that has a very low permeability across the blood–brain barrier (Sipos and Brem, 2000; Fisher, 2002; Liu et al , 2010). …”

“…MIA was administered intraperitoneally 30 min before the onset of experimental asphyxia (Kendall et al , 2006). In some experiments, amiloride (amiloride hydrochloride hydrate; Sigma-Aldrich), the blood–brain barrier-impermeable parent drug of MIA (Sipos and Brem, 2000; Fisher, 2002; Liu et al , 2010), was administered at an identical concentration. Each incidence of loss of righting reflex was given a score of one.…”

Suppression of GABAergic Synaptic Transmission by Azidin: Probable Mechanism of a Seizure-Inducing Side Effect

“…It cannot be ruled out that the action of diminazene aceturate on GABAergic transmission under conditions of our experiments is determined by the action of this drug precisely on the above-mentioned proton-activated channels that are coupled, in some a way, with GABA-activated ones. Such an assumption is indirectly confirmed by the fact that amyloride, another blocker of protonactivated channels, influences considerably the effects induced by application of exogenous GABA [6,7] and GABA-mediated PSCs [8]. Recently, it was found that functional interaction between GABA A receptors and ASIC1a channels is quite possible; a protein complex including both abovementioned receptors has been identified [9].…”

Amiloride and GMQ Allosteric Modulation of the GABA-A ρ1 Receptor: Influences of the Intersubunit Site

“…Amiloride, the prototypical acid-sensing ion channel (ASIC) antagonist, acts as a competitive antagonist for the heteromeric GABA-A abg receptors (Inomata et al, 1988;Fisher, 2002;Liu et al, 2010). The activity of amiloride on the GABA-A r1 receptor remains unclear.…”