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RECEPTORS AND SIGNAL TRANSDUCTION
Department of Physiology and Cell Biology, University of Nevada School of Medicine, Reno, Nevada
Submitted 13 March 2006 ; accepted in final form 15 May 2006
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ABSTRACT |
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inhibitory junction potentials; smooth muscle; enteric nervous system
Traditionally, the repolarization phase of IJPs has been considered secondary to the breakdown or dilution by diffusion of neurotransmitters (i.e., ATP or NO). Reduction of transmitter would lead to cessation of K+ (SK or KNO) channel activation and reestablishment of basal conductances. ATP metabolism by ecto-ATPase is relatively slow and does not account for the rapid repolarization process involved in recovery from the fast IJP (1). We previously suggested (1) that a voltage-dependent inward current may become available at negative potentials and contribute to the active repolarization of fast IJPs.
There are two components of voltage-gated inward current in murine colonic myocytes (25). One current has properties of an L-type Ca2+ current and is sensitive to nicardipine. The second current did not "run down" when cells were dialyzed and was resistant to dihydropyridines (DHP). The DHP-insensitive current was activated at relatively negative potentials (inward current was resolved at potentials as negative as –60 mV) and reversed near 0 mV. The conductance responsible for this current had properties of a voltage-dependent nonselective cation conductance, and the current was termed IVNSCC. IVNSCC may contribute to active repolarization of IJPs due to resetting of these channels during the negative potentials achieved during IJPs. It is also possible that IVNSCC could be regulated by inhibitory neurotransmitters. Here we have investigated the hypothesis that ATP, an inhibitory neurotransmitter responsible for fast IJPs, may activate IVNSCC. We also examined the effects of nucleotides with structures similar to ATP on voltage-dependent inward currents in murine colonic myocytes and examined the second messenger pathway involved in purinergic regulation of IVNSCC.
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METHODS |
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Colons were cut open along the longitudinal axis, pinned out in a Sylgard-lined dish, and washed with Ca2+-free phosphate-buffered saline (PBS) containing (mM) 125 NaCl, 5.36 KCl, 15.5 NaOH, 0.336 Na2HPO4, 0.44 KH2PO4, 10 glucose, 2.9 sucrose, and 11 HEPES and adjusted to pH 7.4 with NaOH. Mucosa and submucosa were removed with fine-tipped forceps. Pieces of muscle were incubated for 8–12 min at 37°C in a Ca2+-free solution containing 4 mg/ml fatty acid-free bovine serum albumin, 2 mg/ml papain, 1 mg/ml collagenase (Worthington Biochemical, Lakewood, NJ), and 1 mM dithiothreitol (DTT). After enzymatic treatment, the muscles were washed with Ca2+-free solution and agitated gently to create a cell suspension. Dispersed smooth muscle cells were stored at 4°C in Ca2+-free solution supplemented with minimum essential medium for suspension culture (S-MEM, Sigma, St. Louis, MO) and (mM) 0.5 CaCl2, 0.5 MgCl2, 4.17 NaHCO3, and 10 HEPES, adjusted to pH 7.4 with Tris. Cells were transferred from the refrigerator to the recording chamber. Drops of the cell suspensions were placed on a glass coverslip forming the bottom of a 300-µl chamber mounted on an inverted microscope and allowed to adhere to the bottom of the chamber for 5 min before recording.
Voltage-clamp methods.
Whole cell voltage-clamp techniques were used to record membrane currents from dissociated smooth muscle cells. Membrane currents were amplified by an Axopatch 1D (Axon Instruments, Foster City, CA) and digitized with an analog-to-digital converter (Digidata 1200, Axon Instruments). Data were collected at 4 kHz, filtered at 1 kHz via Bessel filter, and digitized online with pCLAMP software (version 6.0.4 or 8.1.0, Axon Instruments). The data were analyzed with the use of pCLAMP software (version 8.1.0, Axon Instruments). Pipette resistances were 1–4 M
, and the uncompensated series resistance was between 2 and 4 M. The linear leak current was subtracted digitally. Conventional and perforated whole cell (amphotericin B) patch-clamp techniques were used for recording ionic currents under voltage clamp. Cell capacitance averaged 43 ± 5 pF (n = 7 dialyzed) and 48 ± 5 pF (n = 10 perforated patches), and the series resistances in dialyzed and perforated whole cell configurations were 5.7 ± 0.8 and 7.8 ± 0.6 M, respectively. Experiments were performed at room temperature (between 22 and 25°C).
Solutions and reagents. The external solution used in conventional whole cell recordings contained (in mM) 135 NaCl, 5 KCl, 2 CaCl2, 1.2 MgCl2, 10 glucose, 10 HEPES adjusted to pH 7.4 with Tris (CaPSS). The standard internal solution contained (in mM) 110 CsCl, 30 tetraethylammonium chloride, 10 BAPTA, 5 Na2ATP, 5 MgCl2, and 5 HEPES. This solution was adjusted to pH 7.2 with Tris. Amphotericin B (90 mg/ml) was dissolved in DMSO, sonicated, and diluted in the pipette solution to give a final concentration of 270 µg/ml. U-73122, U-73343, chelerythrine chloride, bisindolylmaleimide I hydrochloride (BIM), and phorbol 12,13-dibutyrate (PDBu) were purchased from Calbiochem (EMD Biosciences, San Diego, CA). All other chemicals were purchased from Sigma. In all experiments, ATP, UTP, UDP, and ADP were dissolved directly in CaPSS (final concentration 1 mM) immediately before application.
RNA isolation and RT-PCR.
Total RNA was isolated from mouse proximal colon tissue (mucosa and submucosa removed) and whole mouse brain with TRIzol reagent (GIBCO, Gaithersburg, MD). Drops of freshly dispersed myocytes were placed on a glass coverslip forming the bottom of a 300-µl chamber mounted on an inverted microscope. Twenty to thirty single cells were collected through applied suction by aspirating them into a wide-bore borosilicate pipette, and the pipette contents were ejected into a sterile 0.5-ml tube. Their characteristic spindle-shaped morphology differentiated smooth muscle cells. Total RNA was isolated with a SNAP total RNA isolation kit (Invitrogen, Carlsbad, CA) per the manufacturer's instructions. First-strand cDNA was prepared from the total RNA with a Superscript Reverse Transcriptase kit (GIBCO). One microgram of total RNA was reverse transcribed with 200 U of reverse transcriptase in a 20-µl reaction containing 25 ng of oligo(dT) primer, dNTPs each at 500 µM, 75 mM KCl, 3 mM MgCl2, 10 mM DTT, and 50 mM Tris·HCl (pH 8.3). As a control, PCR primers specific for 
-actin (GenBank accession no. V01217) nucleotides 2383–2402 and 3071–3091 were used to establish that the cDNA prepared as described above was nongenomic. The -actin-specific primers amplified only the intronless amplification product from all cDNA samples, indicating that these preparations were free of genomic DNA contamination. The cDNA reverse transcription products were amplified with P2Y subtype-specific primers. Gene-specific primers were synthesized based on the reported sequences for P2Y1 (GenBank accession no. NM008772), P2Y2 (GenBank accession no. BC006613), P2Y4 (GenBank accession no. MMU277752), and P2Y6 (GenBank accession no. AF298899). PCR was carried out with AmpliTaq polymerase (PE Biosystems) in a 2300 thermalcycler (PE Biosystems), and PCR fragments were analyzed by gel electrophoresis.
Data analysis. All experimental values are presented as means ± SE, and n refers to the number of cells tested. Differences between the values from different groups were compared with Student's paired t-tests. P values <0.05 were considered significantly different.
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RESULTS |
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Nucleotide effect on two types of inward currents. Purines (adenosine, ADP, and ATP) and pyrimidines (UDP and UTP) act with varying potencies depending on receptor subtype(s) (32). We used the double-pulse protocol described above on colonic myocytes in the perforated-patch configuration and characterized the effects of other nucleotides (ADP, UTP, and UDP) on the two inward currents to further examine the P2 receptor subtypes that mediate the effects of ATP. ADP (1 mM) had no significant effect on IVNSCC (Fig. 3, A–C; n = 10) but decreased IL significantly to 75 ± 1% of the control level (Fig. 3, A, B, and D; n = 15). UTP (1 mM) increased IVNSCC to 169 ± 7% of the control peak current at –45 mV (Fig. 4, A–C; n = 15) and decreased IL by 30 ± 4% at 0 mV (Fig. 4, A, B, and D; n = 10). UDP (1 mM) increased the amplitude of IVNSCC to 157 ± 6% of the control peak current (Fig. 5, A–C; n = 10) and decreased IL by 19 ± 2% (Fig. 5, A, B, and D; n = 10). Thus the order of effectiveness of nucleotides on IVNSCC was UTP = UDP > ATP >> ADP (Fig. 6). There was no variation in effectiveness of the nucleotides on the amplitude of IL (data not shown), suggesting that the effects of nucleotides on IL may not be mediated by P2Y receptors. The metabotrophic P2Y4 receptor has been otherwise referred to as uridine nucleotide-specific receptor and has a nucleotide potency that matches the order of effectiveness of nucleotides on IVNSCC (7, 15). These data suggest that the P2Y4 isoform of purine receptors could be responsible for mediating the actions of nucleotides on IVNSCC in murine colonic myocytes.
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-Actin primers were used as a control for cDNA integrity, and a no-template control was included to rule out DNA contamination (Fig. 8D). In summary, all P2Y transcripts examined (i.e., P2Y1, P2Y2, P2Y4, and P2Y6) were present in brain and colonic muscles; however, only P2Y1 and P2Y4 transcripts were expressed in colonic myocytes.
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ATP increased IVNSCC from –91 ± 18 pA to –153 ± 32 pA at –45 mV. The PLC inhibitor U-73122 (100 nM) completely reversed the effect of ATP, reducing current amplitude to –93 ± 25 pA in the continued presence of ATP (Fig. 9, A–C; n = 7, P < 0.01). An inactive analog of U-73122, U-73343, had no effect on the ATP response (Fig. 9, D–F).
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-Phorbol ester, an inactive analog, had no significant effect on responses to ATP (Fig. 11, E and F).
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DISCUSSION |
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The nitrergic component of enteric inhibitory responses appears to be mediated through close, synaptic-like contacts between nerve varicosities and intramuscular interstitial cells of Cajal [ICC-IM or ICC-deep muscular plexus (DMP)] in the GI tract (see Refs. 9, 41, 42). In contrast to nitrergic responses, the effects of ATP may be due to direct effects on smooth muscle cells because previous experiments showed that purinergic (i.e., apamin sensitive) responses were normal, or even somewhat enhanced, in animals without ICC-IM (9, 34). These observations suggest that neurally released ATP escapes the synaptic region between ICC-IM and nerve varicosities and has direct effects on smooth muscle cells.
Two general types of P2 purinoreceptors have been characterized in pharmacological and molecular experiments. One group of purinoreceptors is activated by ,-methylene ATP and inhibited by suramin and PPADS. The other group is activated by adenosine 5'-O-2-thiodiphosphate (ADPS) and is resistant to suramin and PPADS (8, 29, 45, 46). In guinea pig ileal circular myocytes, ATP induced the apamin-sensitive fast IJP, which was antagonized by reactive blue 2, a purinergic receptor antagonist (17). In human jejunal circular smooth muscle, ATP mediates fast IJPs through an ADPS-sensitive P2 receptor (46). There is growing evidence to support a role for P2Y receptors in activation of SK channels as well as in production of Ca2+ puffs, a response that is inhibited by PLC inhibitors, IP3 receptor antagonists, and PPADS (6, 28). These events trigger the activation of SK channels and apamin-sensitive IJPs (24). Interestingly, exogenous ATP evoked a biphasic change in the membrane potential, which consisted of an initial hyperpolarization followed by a long-lasting depolarization, suggesting that ATP may not only function as an inhibitory neurotransmitter but may also have a role as an excitatory neurotransmitter (11, 27, 39). Purine-dependent rebound excitation may be another explanation for the depolarization, but a mechanism for such a phenomenon has not been described. Thus far, pharmacological approaches to differentiate among purinoreceptor subtypes are not definitive.
In a recent study (1) we investigated a mechanism of active repolarization during which IVNSCC appears to participate in the restoration of resting membrane potentials after apamin-sensitive (fast) IJPs and responses to localized application of ATP. IVNSCC activates at low threshold potentials (inward current was resolved at potentials as low as –60 mV), reverses close to 0 mV, and inactivates and recovers from inactivation very rapidly (full recovery within 300 ms at 31°C; see Ref. 25). These properties render IVNSCC only weakly available at the resting potentials of colonic myocytes, and hyperpolarization increases availability. In the present study we found that ATP increased the amplitude of IVNSCC. Thus during ATP-induced responses ATP first causes hyperpolarization through activation of SK channels, but there is rapid reversal of hyperpolarization ("active repolarization") due to activation of IVNSCC by ATP. The time course of activation of SK channels and IVNSCC is likely to be due to the fact that channels responsible for IVNSCC must be reset (half-inactivation voltage was –65 mV; see Ref. 25) before they can be activated. IVNSCC would tend to inactivate during repolarization of IJPs and would cease to participate in repolarization at around –50 mV. However, by this point in the inhibitory response the effects of NO begin to dominate, producing the slow IJP. Therefore, this sequence may explain why ATP has only transient effects during the time course of IJPs.
Our data suggest that the effects of nucleotides on IVNSCC may be mediated by P2Y4 receptors. P2Y4 receptors are implicated for the following reasons. These receptors are expressed by colonic myocytes. The order of effectiveness of nucleotides on IVNSCC was UTP = UDP > ATP > ADP. This is a characteristic order for P2Y4 receptors (14). PPADS had no effect on the ATP response, suggesting that ATP may act through a PPADS-resistant P2Y receptor (e.g., P2Y2, P2Y4). Previous studies have shown that P2Y4 receptors stably transfected into 1321N1 cells are relatively insensitive to PPADS (13).
In contrast to the effect of ATP on IVNSCC, we previously demonstrated (24) that the activation of SK channels by ATP in murine colonic myocytes was blocked by preincubation with PPADS. As shown here, PPADS did not inhibit ATP stimulation of IVNSCC. Thus nucleotides may act through at least two types of purinergic receptors: a PPADS-sensitive receptor (possibly P2Y1) that is coupled to activation of SK channels and hyperpolarization and a PPADS-resistant receptor that augments IVNSCC and may contribute to active repolarization of IJPs. ATP, acting through P2Y4 receptors, appears to stimulate IVNSCC in murine colonic myocytes.
Nucleotides binding to purinoreceptors may exert their effects through G protein-coupled mechanisms, which activate PLC (14, 30). Activation of PLC leads to production of IP3 (which increases intracellular Ca2+) and DAG, both of which can activate PKC. Thus we considered activation of PKC as a logical mechanism to mediate the effects of nucleotides on IVNSCC. The PLC inhibitor U-73122 completely reversed the effects of ATP on IVNSCC. The PKC inhibitors chelerythrine and BIM had the same effects as the PLC inhibitor on the ATP response. Finally, a PKC activator (PDBu) mimicked the effects of ATP on IVNSCC. These findings suggest a minimal mechanism for the effects of nucleotides on IVNSCC: ATP (or a related nucleotide) binds to P2Y4 receptors and activates Gq/11-coupled activation of PLC. Liberation of DAG and IP3 lead to activation of PKC. PKC, presumably via a phosphorylation step, activates IVNSCC.
In summary, transmural nerve stimulation of the murine colon evokes a fast IJP followed by repolarization toward the resting membrane potential. Traditionally, the repolarization phase of the IJP has been considered to result from passive breakdown of ATP in the postsynaptic volume and a decrease in K+ conductances (SK). Our data suggest the following novel sequence of channel activation during IJPs: Binding of P2Y receptors leads to formation of IP3 and DAG. Release of intracellular Ca2+ via IP3 receptor-operated Ca2+ channels activates SK channels and causes rapid hyperpolarization toward EK. Hyperpolarization leads to resetting of IVNSCC channels that are simultaneously under stimulatory drive from PLC activation. When the availability of IVNSCC channels increases, inward current tends to drive membrane potential back toward the resting potential. We have referred to this step as active repolarization of IJPs, and it appears that ATP, in addition to initiating the hyperpolarization phase of IJPs, is also involved in stimulating the active repolarization of these events. This action shortens the duration of IJPs and greatly reduces the average inhibitory drive of enteric inhibitory junction potentials. IVNSCC is a unique conductance in GI smooth muscles and therefore could provide a target for drugs to regulate colonic motility.
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GRANTS |
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FOOTNOTES |
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The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
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REFERENCES |
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2. Bartho L, Lenard L Jr, and Szigeti R. Nitric oxide and ATP co-mediate the NANC relaxant response in the guinea-pig taenia caeci. Naunyn Schmiedebergs Arch Pharmacol 358: 496–499, 1998.[CrossRef][ISI][Medline]
3. Bauer V. NANC transmission in intestines and its pharmacological modulation. Acta Neurobiol Exp (Warsz) 53: 65–77, 1993.[Medline]
4. Bauer V and Kuriyama H. The nature of non-cholinergic, non-adrenergic transmission in longitudinal and circular muscles of the guinea-pig ileum. J Physiol 332: 375–391, 1982.
5. Bauer V and Matusak O. The non-adrenergic non-cholinergic innervation and transmission in the small intestine. Arch Int Pharmacodyn Ther 280: 137–163, 1986.[ISI][Medline]
6. Bayguinov O, Hagen B, Bonev AD, Nelson MT, and Sanders KM. Intracellular calcium events activated by ATP in murine colonic myocytes. Am J Physiol Cell Physiol 279: C126–C135, 2000.
7. Bogdanov YD, Wildman SS, Clements MP, King BF, and Burnstock G. Molecular cloning and characterization of rat P2Y4 nucleotide receptor. Br J Pharmacol 124: 428–430, 1998.[CrossRef][ISI][Medline]
8. Bultmann R, Dudeck O, and Starke K. Evaluation of P2-purinoceptor antagonists at two relaxation-mediating P2-purinoceptors in guinea-pig taenia coli. Naunyn Schmiedebergs Arch Pharmacol 353: 445–451, 1996.[ISI][Medline]
9. Burns AJ, Lomax AE, Torihashi S, Sanders KM, and Ward SM. Interstitial cells of Cajal mediate inhibitory neurotransmission in the stomach. Proc Natl Acad Sci USA 93: 12008–12013, 1996.
10. Burnstock G. Review lecture. Neurotransmitters and trophic factors in the autonomic nervous system. J Physiol 313: 1–35, 1981.
11. Burnstock G, Cocks T, Crowe R, and Kasakov L. Purinergic innervation of the guinea-pig urinary bladder. Br J Pharmacol 63: 125–138, 1978.[ISI]
12. Bywater RA and Taylor GS. Non-cholinergic excitatory and inhibitory junction potentials in the circular smooth muscle of the guinea-pig ileum. J Physiol 374: 153–164, 1986.
13. Charlton SJ, Brown CA, Weisman GA, Turner JT, Erb L, and Boarder MR. Cloned and transfected P2Y4 receptors: characterization of a suramin and PPADS-insensitive response to UTP. Br J Pharmacol 119: 1301–1303, 1996.[ISI]
14. Communi D, Motte S, Boeynaems JM, and Pirotton S. Pharmacological characterization of the human P2Y4 receptor. Eur J Pharmacol 317: 383–389, 1996.[CrossRef][ISI][Medline]
15. Communi D, Pirotton S, Parmentier M, and Boeynaems JM. Cloning and functional expression of a human uridine nucleotide receptor. J Biol Chem 270, 30849–30852, 1995.
16. Crist JR, He XD, and Goyal RK. Chloride-mediated inhibitory junction potentials in opossum esophageal circular smooth muscle. Am J Physiol Gastrointest Liver Physiol 261: G752–G762, 1991.
17. Crist JR, He XD, and Goyal RK. Both ATP and the peptide VIP are inhibitory neurotransmitters in guinea-pig ileum circular muscle. J Physiol 447: 119–131, 1992.
18. Dalziel HH, Thornbury KD, Ward SM, and Sanders KM. Involvement of nitric oxide synthetic pathway in inhibitory junction potentials in canine proximal colon. Am J Physiol Gastrointest Liver Physiol 260: G789–G792, 1991.
19. Hirst GD, Bywater RA, Teramoto N, and Edwards FR. An analysis of inhibitory junction potentials in the guinea-pig proximal colon. J Physiol 558: 841–855, 2004.
20. Inoue R. Effect of external Cd2+ and other divalent cations on carbachol-activated non-selective cation channels in guinea-pig ileum. J Physiol 442: 447–463, 1991.
21. Inoue R and Isenberg G. Acetylcholine activates nonselective cation channels in guinea pig ileum through a G protein. Am J Physiol Cell Physiol 258: C1173–C1178, 1990.
22. Keef KD, Du C, Ward SM, McGregor B, and Sanders KM. Enteric inhibitory neural regulation of human colonic circular muscle: role of nitric oxide. Gastroenterology 105: 1009–1016, 1993.[ISI][Medline]
23. Koh SD, Campbell JD, Carl A, and Sanders KM. Nitric oxide activates multiple potassium channels in canine colonic smooth muscle. J Physiol 489: 735–743, 1995.
24. Koh SD, Dick GM, and Sanders KM. Small-conductance Ca2+-dependent K+ channels activated by ATP in murine colonic smooth muscle. Am J Physiol Cell Physiol 273: C2010–C2021, 1997.
25. Koh SD, Monaghan K, Ro S, Mason HS, Kenyon JL, and Sanders KM. Novel voltage-dependent non-selective cation conductance in murine colonic myocytes. J Physiol 533: 341–355, 2001.
26. Koh SD, Monaghan K, Sergeant GP, Ro S, Walker RL, Sanders KM, and Horowitz B. TREK-1 regulation by nitric oxide and cGMP-dependent protein kinase. An essential role in smooth muscle inhibitory neurotransmission. J Biol Chem 276: 44338–44346, 2001.
27. Komori S and Ohashi H. Some characteristics of transmission from non-adrenergic, non-cholinergic excitatory nerves to the smooth muscle of the chicken. J Auton Nerv Syst 6: 199–210, 1982.[CrossRef][ISI][Medline]
28. Kong ID, Koh SD, and Sanders KM. Purinergic activation of spontaneous transient outward currents in guinea pig taenia colonic myocytes. Am J Physiol Cell Physiol 278: C352–C362, 2000.
29. Lambrecht G, Friebe T, Grimm U, Windscheif U, Bungardt E, Hildebrandt C, Baumert HG, Spatz-Kumbel G, and Mutschler E. PPADS, a novel functionally selective antagonist of P2 purinoceptor-mediated responses. Eur J Pharmacol 217: 217–219, 1992.[CrossRef][ISI][Medline]
30. Murthy KS and Makhlouf GM. Coexpression of ligand-gated P2X and G protein-coupled P2Y receptors in smooth muscle. Preferential activation of P2Y receptors coupled to phospholipase C (PLC)-1 via Gq/11 and to PLC-3 via G
i3. J Biol Chem 273: 4695–4704, 1998.
31. Park KJ, Baker SA, Cho SY, Sanders KM, and Koh SD. Sulfur-containing amino acids block stretch-dependent K+ channels and nitrergic responses in the murine colon. Br J Pharmacol 144: 1126–1137, 2005.[CrossRef][ISI][Medline]
32. Ralevic V and Burnstock G. Receptors for purines and pyrimidines. Pharmacol Rev 50: 413–492, 1998.
33. Romey G and Lazdunski M. The coexistence in rat muscle cells of two distinct classes of Ca2+-dependent K+ channels with different pharmacological properties and different physiological functions. Biochem Biophys Res Commun 118: 669–674, 1984.[CrossRef][ISI][Medline]
34. Sergeant GP, Large RJ, Beckett EA, McGeough CM, Ward SM, and Horowitz B. Microarray comparison of normal and W/Wv mice in the gastric fundus indicates a supersensitive phenotype. Physiol Genomics 11: 1–9, 2002.
35. Shuttleworth CW, Conlon SB, and Sanders KM. Regulation of citrulline recycling in nitric oxide-dependent neurotransmission in the murine proximal colon. Br J Pharmacol 120: 707–713, 1997.[CrossRef][ISI][Medline]
36. Sneddon P. Electrophysiology of autonomic neuromuscular transmission involving ATP. J Auton Nerv Syst 81: 218–224, 2000.[CrossRef][ISI][Medline]
37. Spencer NJ, Bywater RA, and Taylor GS. Disinhibition during myoelectric complexes in the mouse colon. J Auton Nerv Syst 71: 37–47, 1998.[CrossRef][ISI][Medline]
38. Stark ME, Bauer AJ, Sarr MG, and Szurszewski JH. Nitric oxide mediates inhibitory nerve input in human and canine jejunum. Gastroenterology 104: 398–409, 1993.[ISI][Medline]
39. Venkova K, Milne A, and Krier J. Contractions mediated by alpha1-adrenoceptors and P2-purinoceptors in a cat colon circular muscle. Br J Pharmacol 112: 1237–1243, 1994.[ISI]
40. Vogalis F, Zhang Y, and Goyal RK. An intermediate conductance K+ channel in the cell membrane of mouse intestinal smooth muscle. Biochim Biophys Acta 1371: 309–316, 1998.[Medline]
41. Ward SM, Beckett EA, Wang X, Baker F, Khoyi M, and Sanders KM. Interstitial cells of Cajal mediate cholinergic neurotransmission from enteric motor neurons. J Neurosci 20: 1393–1403, 2000.
42. Ward SM and Sanders KM. Upstroke component of electrical slow waves in canine colonic smooth muscle due to nifedipine-resistant calcium current. J Physiol 455: 321–337, 1992.
43. Ward SM, McLaren GJ, and Sanders KM. Interstitial cells of Cajal in the deep muscular plexus mediate enteric motor neurotransmission in the small intestine. J Physiol 573: 147–159, 2006.
44. Waterman SA and Costa M. The role of enteric inhibitory motoneurons in peristalsis in the isolated guinea-pig small intestine. J Physiol 477: 459–468, 1994.
45. Windscheif U, Pfaff O, Ziganshin AU, Hoyle CH, Baumert HG, Mutschler E, Burnstock G, and Lambrecht G. Inhibitory action of PPADS on relaxant responses to adenine nucleotides or electrical field stimulation in guinea-pig taenia coli and rat duodenum. Br J Pharmacol 115: 1509–1517, 1995.[ISI]
46. Xue L, Farrugia G, Sarr MG, and Szurszewski JH. ATP is a mediator of the fast inhibitory junction potential in human jejunal circular smooth muscle. Am J Physiol Gastrointest Liver Physiol 276: G1373–G1379, 1999.
47. Zagorodnyuk V and Maggi CA. Pharmacological evidence for the existence of multiple P2 receptors in the circular muscle of guinea-pig colon. Br J Pharmacol 123: 122–128, 1998.[CrossRef][ISI][Medline]
48. Zagorodnyuk V, Santicioli P, Maggi CA, and Giachetti A. The possible role of ATP and PACAP as mediators of apamin-sensitive NANC inhibitory junction potentials in circular muscle of guinea-pig colon. Br J Pharmacol 119: 779–786, 1996.[ISI]
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) and L-type Ca2+ current (IL; 
) as a function of time (A) and sample traces (B) in 1 cell in the absence and presence of ATP. Note the typical rundown of IL in a dialyzed cell shown in A. Inset in B denotes the voltage protocol for both currents. Letters a–d in A indicate which points were used for sample traces in B. C and D: summed results for IVNSCC (n = 8) and IL (n = 12), respectively. ATP had no significant effect on either current. The significant decrease in IL was due to rundown. Bars represent mean ± SE peak current. *P < 0.05.
Deceased 19 December 2003. 