A novel calcium-sensitive potassium conductance is coupled to P2X₃ subunit containing receptors in myenteric neurons of guinea pig ileum.

Ren, J.; Galligan, J. J.

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 P2X1 and P2X3 subunit containing receptors, depolarized 103 neurons (85%). Pyridoxal-phosphate-6-azophenyl-2′,4′ disulfonic acid (10 μmol 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 μmol L−1), an antagonist that can block P2X3 receptors. Ivermectin (10 μmol L−1), a modulator of P2X4 and P2X4/6 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 Ca2+ solutions. Blockers of large, intermediate and small conductance Ca2+-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 P2X3 subunit containing P2X receptors. P2X receptors couple to activation of a Ca2+-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.

ELECTROPHYSIOLOGY; NERVOUS system; ION channels; NEURONS; NEURAL transmission

Neurogastroenterology & Motility, 2007, Vol 19, Issue 11, p912

1350-1925

Academic Journal

10.1111/j.1365-2982.2007.00952.x