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The electrophysiological and pharmacological properties of nicotinic acetylcholine receptors (nAChRs) were studied in guinea pig small intestinal myenteric neurons maintained in culture or in acutely isolated preparations. Acetylcholine and nicotine caused inward currents that desensitized in ϳ4 s. The current-voltage (I-V) relationship rectified inwardly with a reversal potential near 0 mV. The agonist rank order potency was 1,1-dimethyl-4-phenylpiperazinium Ͼ acetylcholine ϭ nicotine Ͼ Ͼ cytisine. Agonistinduced currents were blocked by nAChR antagonists with a rank order potency of mecamylamine Ͼ hexamethonium Ͼ dihydro-␤-erythroidine (DH␤E); mecamylamine and DH␤E exhibit high potency at ␤4 and ␤2 subunit-containing nAChRs, respectively. ␣-Bungarotoxin (0.1 M) or ␣-methyllycaconitine (0.1 M), antagonists that block nAChRs containing ␣7 subunits, did not affect acetylcholine-induced responses. Immunohistochemical studies revealed that nearly every neuron in culture was labeled by an antibody (mAb35) that recognizes nAChR ␣3 and ␣5 subunits. Antibodies selective for ␣3, ␣5, or ␤2 subunits also stained most neurons, whereas an ␣7 subunit antibody revealed very few neurons. In neurons in the intact myenteric plexus from newborn and adult guinea pigs, local application of acetylcholine (1 mM) and cytisine (1 mM) caused similar amplitude depolarizations, and these responses were blocked by nAChR antagonists with a rank order potency of mecamylamine Ͼ hexamethonium Ͼ DH␤E. These data indicate that myenteric neurons maintained in culture predominately express nAChRs composed of ␣3, ␣5, ␤2, and ␤4 subunits. These subunits may be in a homogenous population of receptors with unique pharmacological properties, or multiple receptors of different subunit composition may be expressed by individual neurons.In the nervous system, nAChRs are ligand-gated cation channels composed of pentameric combinations of 11 subunits (␣2-␣9; ␤2-␤4) (Sargent, 1993;Lukas et al., 1999). The specific subunit composition yields receptors with pharmacological and electrophysiological properties that are unique to that subunit combination (Luetje and Patrick, 1991;Gerzanich et al., 1998). For example, antagonists can discriminate among nAChRs with different subunit compositions. ␣-Methyllycaconitine and ␣-bungarotoxin (␣-BGT) are potent and selective antagonists of ␣7 subunit-containing nAChRs (Couturier et al., 1990;Ward et al., 1990). Receptors composed of the ␣4␤2 or ␣3␤2 subunit combinations are more sensitive to block by dihydro-␤-erythroidine (DH␤E) than receptors composed of other subunit pairs. Alternatively, mecamylamine has high affinity for nAChRs composed of ␣3␤4 subunits (Albuquerque et al., 1997).There are two main classes of neuron in the enteric nervous system: S neurons and AH neurons. S neurons are enteric interneurons or motor neurons (Kunze and Furness, 1999). S neurons receive fast excitatory synaptic input mediated partly by acetylcholine acting at nAChRs (Galligan and Bertrand, 1994). Studies of the pharmacological p...

This study characterized P2X receptors in guinea pig ileum myenteric S neurons (n = 124) in vitro using electrophysiological methods. ATP or alpha,beta-methylene ATP (alpha,beta-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 micromol L(-1)) blocked ATP- and alpha,beta-mATP-induced depolarizations. ATP-induced depolarizations and fast excitatory postsynaptic potentials (fEPSPs) were reduced by trinitrophenyl-ATP (10 micromol L(-1)), an antagonist that can block P2X(3) receptors. Ivermectin (10 micromol L(-1)), a modulator of P2X(4) and P2X(4/6) receptors, had no effect on alpha,beta-mATP-induced depolarizations. In 58% of neurons, the alpha,beta-mATP induced-depolarization was followed by an afterhyperpolarization (AHP) (P2X-AHP). Under voltage clamp, alpha,beta-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.

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New type of substituted 1H‐pyrazole‐4‐carboxamides were obtained by regioselective synthesis under the catalysis of different bases. The structures of the title compounds were confirmed by elemental analysis, 1H NMR, IR, MS and X‐ray crystallography. Compounds 1 were transacylated into their corresponding amides 3 in the presence of sodium hydride. Preliminary bioassays indicated that some compounds showed fungicidal activities against Rhizoctonia solani and Sclerotinia sclerotiorum.