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A novel calcium‐sensitive potassium conductance is coupled to P2X 3 subunit containing receptors in myenteric neurons of guinea pig ileum
Author(s) -
Ren J.,
Galligan J. J.
Publication year - 2007
Publication title -
neurogastroenterology and motility
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.489
H-Index - 105
eISSN - 1365-2982
pISSN - 1350-1925
DOI - 10.1111/j.1365-2982.2007.00952.x
Subject(s) - reversal potential , biophysics , neurotransmission , chemistry , agonist , excitatory postsynaptic potential , purinergic receptor , receptor , patch clamp , depolarization , afterhyperpolarization , neuroscience , biochemistry , biology
This study characterized P2X receptors in guinea pig ileum myenteric S neurons ( n = 124) in vitro using electrophysiological methods. ATP or α , β ‐methylene ATP ( α , β ‐mATP), an agonist at P2X 1 and P2X 3 subunit containing receptors, depolarized 103 neurons (85%). Pyridoxal‐phosphate‐6‐azophenyl‐2′,4′ disulfonic acid (10 μ mol L −1 ) blocked ATP‐ and α , β ‐mATP‐induced depolarizations. ATP‐induced depolarizations and fast excitatory postsynaptic potentials (fEPSPs) were reduced by trinitrophenyl‐ATP (10 μ mol L −1 ), an antagonist that can block P2X 3 receptors. Ivermectin (10 μ mol L −1 ), a modulator of P2X 4 and P2X 4/6 receptors, had no effect on α , β ‐mATP‐induced depolarizations. In 58% of neurons, the α , β ‐mATP induced‐depolarization was followed by an afterhyperpolarization (AHP) (P2X‐AHP). Under voltage clamp, α , β ‐mATP induced an inward current followed by an outward current which reversed polarity at 0 and −80 mV respectively. The P2X‐AHP was reduced in low extracellular Ca 2+ solutions. Blockers of large, intermediate and small conductance Ca 2+ ‐activated K + channels or voltage‐gated K + channels did not inhibit the P2X‐AHP. Half of the neurons exhibiting the P2X‐AHP contained nitric oxide synthase (NOS)‐immunoreactivity (ir). In summary, NOS‐ir S neurons express P2X 3 subunit containing P2X receptors. P2X receptors couple to activation of a Ca 2+ ‐activated K + conductance that mediates an AHP. As P2X receptors contribute to fEPSPs, the P2X‐AHP may modulate S neuron excitability during purinergic synaptic transmission.