Cross-inhibition between nicotinic acetylcholine receptors and P2X receptors in myenteric neurons and HEK-293 cells

Abstract

Decker DA, Galligan JJ. Cross-inhibition between nicotinic acetylcholine receptors and P2X receptors in myenteric neurons and HEK-293 cells. Am J Physiol Gastrointest Liver Physiol 296: G1267-G1276, 2009. First published April 2, 2009 doi:10.1152/ajpgi.00048.2009.-The enteric nervous system (ENS) controls gut function. P2X receptors and nicotinic acetylcholine receptors (nAChRs) are ligand-gated cation channels that mediate fast synaptic excitation in the ENS. Close molecular coupling in enteric neuronal membranes contributes to a mutually inhibitory interaction between these receptors; this effect is called cross-inhibition. We studied the molecular mechanisms responsible for cross-inhibition. Whole cell patch-clamp techniques were used to measure P2X-and nAChR-mediated currents in cultured enteric neurons and HEK-293 cells. In cultured myenteric neurons, ACh (3 mM) and ATP (1 mM) coapplication evoked an inward current that was only 57 Ϯ 6% (P Ͻ 0.05) of the predicted current that would have occurred if the two populations of channels were activated independently. In HEK-293 cells coexpressing ␣ 3 ␤ 4 nAChR/P2X 2 receptors, coapplication of ATP and ACh caused a current that was 58 Ϯ 7% of the predicted current (P Ͻ 0.05). To test the importance of P2X subunit COOH-terminal tail length on cross-inhibition, P2X 3 and P2X4 subunits, which have shorter COOHterminal tails, were studied. Cross-inhibition with ␣ 3␤4 nAChRs and P2X 3 or P2X4 subunits was similar to that occurring with P2X2 subunits. P2X receptor or ␣ 3␤4 nAChR desensitization did not prevent receptor cross-inhibition. These data indicate that the ␣ 3␤4-P2X receptor interaction is not restricted to P2X 2 subunits. In addition, active and desensitized conformations of the P2X receptor inhibit nAChR function. These molecular interactions may modulate the function of synapses that use ATP and ACh as fast synaptic transmitters in the ENS. enteric nervous system; synaptic transmission; ligand-gated ion channels THE ENTERIC NERVOUS SYSTEM (ENS) is the division of the autonomic nervous system (ANS) that controls gastrointestinal function (8). Although parasympathetic, sympathetic, and sensory nerves supply the intestine, the ENS can control gut function independently from central nervous system control. This is possible because the ENS contains all the neural elements needed for reflex control of gastrointestinal function (10, 12). These elements include motoneurons, interneurons, and sensory neurons that respond to mechanical and chemical stimuli provided by intraluminal content (9).There are two classes of ligand-gated ion channel receptors that mediate fast synaptic excitation of enteric neurons; cysloop receptors and P2X receptors. Cys-loop receptors include nicotinic acetylcholine receptors (nAChRs), 5-HT 3 receptors, and GABA A receptors. Cys-loop receptors are pentameric, and each subunit has four transmembrane domains and extracellular NH 2 -and COOH-terminal tails (17,18). Neuronal nAChRs are composed of two ␣-and three ␤-subunits; there are eight ne...

Subtype-Specific Mechanisms for Functional Interaction between α6β4* Nicotinic Acetylcholine Receptors and P2X Receptors

“…Other investigators have seen different roles for desensitization for different receptor combinations (Nakazawa, 1994;Khakh et al, 2000;Decker and Galligan, 2009), indicating that the detailed cross-inhibitory mechanism varies within the P2X and Cys-loop receptor subtypes involved in the interaction.…”

Novel functional roles for enteric glia in the gastrointestinal tract

“…Cross inhibition of enteric purinergic and nicotinic signalling pathways suggests that nicotinic receptor desensitization, as would occur during prolonged stimulation periods, could potentiate purinergic pathways. 59 Presumably, during brief, physiological activation of neuronal nicotinic circuits, the low levels of ATP released are insufficient to stimulate large Ca 2+ responses throughout the enteric glial network. However, with a sufficiently strong, prolonged, or pathophysiological stimulus, enteric neurons release high levels of ATP that recruit large responses in the surrounding glial cells.…”

Regulation of GABAA Receptor Dynamics by Interaction with Purinergic P2X2 Receptors

“…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)).…”