Cross‐inhibitory interactions between GABA_A and P2X channels in myenteric neurones

Abstract

Inhibitory interactions between GABA(A)[induced by gamma-aminobutyric acid (GABA)] and P2X [activated by adenosine 5'-triphosphate (ATP)] receptors of myenteric neurones from the guinea pig small intestine were characterized using whole-cell recordings. Currents induced by GABA (I(GABA)) or ATP (I(ATP)) were inhibited by picrotoxin or pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid, respectively. Currents induced by GABA + ATP (I(GABA+ATP)) were only as large as the current induced by the most effective transmitter, revealing current occlusion. This occlusion requires maximal activation of at least one of these receptors. Sequential applications of neurotransmitters, and kinetic and pharmacological properties of I(GABA+ATP) indicate that they are carried through both GABA(A) and P2X channels. ATP did not affect I(GABA) in neurones: (i) in which P2X channels were not present; (ii) after inhibiting P2X channels with Ca2+ (iii) in the presence of pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid, a P2X receptor antagonist; (iv) after P2X receptor desensitization or (v) at I(ATP) reversal potential. Similarly, GABA did not affect P2X-mediated currents in neurones: (i) in which GABA(A) channels were not present; (ii) in the presence of picrotoxin, a GABA(A) channel blocker; (iii) after GABA(A) receptor desensitization or (iv) at the I(GABA) reversal potential. Current occlusion occurred as fast as current activation and it was still present in the absence of Ca2+, at 11 degrees C, after adding to the pipette solution a cocktail of protein kinase inhibitors (staurosporine + genistein + K-252a), after substituting the GTP in the pipette with GDP-beta-S and after treating the cells with N-ethylmaleimide. Taken together, all of these results are consistent with a model of cross-inhibition between GABA(A) and P2X.

Cross-talk between P2X4 and γ-Aminobutyric Acid, Type A Receptors Determines Synaptic Efficacy at a Central Synapse

“…In our current work, cross-inhibition between recombinant P2X4 and GABA A receptors was voltage-and ion-independent, which is consistent with the previous studies of other P2X subtypes and cys loop receptor members (12)(13)(14)(15)(16)(17)(18)(19)21). In addition, our biochemical and immunohistochemical experiments in transfected cells and SF-1 GFP-positive neurons further provide the cellular mechanisms that mediate cross-inhibition between the two distinct receptors.…”

“…ATP is released either with an inhibitory neurotransmitter, GABA 4 (7)(8)(9)(10) or with an excitatory neurotransmitter, glutamate in the CNS (4,11). Recent studies have clearly demonstrated the interactions of P2X receptors with other ligand-gated channels, including 5-hydroxytryptamine, GABA A , or nicotinic receptors in recombinant expression and cell culture preparations (12)(13)(14)(15)(16)(17)(18)(19)(20)(21). It thus appears that P2X receptors prefer to interact with other receptors rather than act independently.…”

Purinergic receptors and synaptic transmission in enteric neurons

“…Simultaneous activation of nicotinic and P2X receptors produces a response that is smaller in amplitude than the predicted sum of responses caused by individual activation of each receptor. Recently, GABA A currents or current produced by activation of 5-HT 3 receptors has also been found to occlude P2X currents in much the same way [71,72]. Taken together, these data suggest that a functional interaction between P2X and other ligand-gated channels may be the norm and thus physiologically important.…”

Regulation of GABAA Receptor Dynamics by Interaction with Purinergic P2X2 Receptors

“…GABA A Rs and P2X 2 Rs have been demonstrated to be co-localized and to functionally interact with each other in the spinal cord and dorsal root ganglion (20,21). Simultaneous activation of GABA A Rs and P2X 2 Rs results in nonadditive currents or "cross-talk" of the receptors (22,23). Similar cross-talk was also observed between P2X 2 Rs and other members of the cys-loop receptor family (24 and references therein).…”

“…As members from the P2XR family have been demonstrated to show cross-talk with not only GABA A Rs (20,22,23,58) but also with several other members of Cys loop receptors, which includes 5-hydroxytryptamine/serotonin type 3 receptors (59, 60), GABA C receptors (54), and nicotinic acetylcholine receptors (61,62), association of P2X 2 Rs with other receptors and co-trafficking to specific locations at the cell surface in fact may be a general phenomenon. Indeed, such Cys loop receptor-mediated recruitment to the cell surface is possibly not restricted to P2X 2 Rs as several other members of P2XR family are now known to interact with GABA A Rs (P2X 1 , P2X 4 , and P2X 5 , experiments not shown; P2X 3 (20,58)) and nicotinic receptors (P2X 2 , P2X 3 , and P2X 4 (61)).…”