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McHale NG, Thornbury KD, Hollywood MA. 5-HT inhibits spontaneous contractility of isolated sheep mesenteric lymphatics via activation of 5-HT(4) receptors. Microvasc Res 2000; 60:261-8. [PMID: 11078642 DOI: 10.1006/mvre.2000.2275] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Spontaneous isometric contractions were measured in rings of sheep mesenteric lymphatic vessels in vitro. 5-Hydroxytryptamine (5-HT) produced a concentration-dependent decrease in spontaneous contraction frequency and force which was not antagonised by either the nonspecific 5-HT(1)/5-HT(2) receptor antagonist methysergide (1 microM) or the 5-HT(3) receptor antagonist ondansetron (1 microM). The 5-HT(4) receptor agonist BIMU-8 mimicked the inhibitory effect of 5-HT and its effects were abolished by the 5-HT(4) receptor antagonist DAU 6285 (1 microM). DAU-6285 also abolished the inhibitory effect of 5-HT and unmasked a weak excitatory response, which was mimicked by the 5-HT(2) receptor agonist alpha-methyl-5-hydroxytryptamine maleate. This excitatory response was, in turn, blocked by the 5-HT(2) receptor antagonist pirenperone (1 microM). The results of this study suggest that sheep mesenteric lymphatics possess both 5-HT(4) receptors and 5-HT(2) receptors. The inhibitory 5-HT(4) receptor appeared to be the predominant subtype since the excitatory response to 5-HT could only be observed in the presence of the 5-HT(4) receptor antagonist DAU 6285.
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Toland HM, McCloskey KD, Thornbury KD, McHale NG, Hollywood MA. Ca(2+)-activated Cl(-) current in sheep lymphatic smooth muscle. Am J Physiol Cell Physiol 2000. [PMID: 11029279 DOI: 10.1117/12.842579] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/14/2023]
Abstract
Freshly dispersed sheep mesenteric lymphatic smooth muscle cells were studied at 37 degrees C using the perforated patch-clamp technique with Cs(+)- and K(+)-filled pipettes. Depolarizing steps evoked currents that consisted of L-type Ca(2+) [I(Ca(L))] current and a slowly developing current. The slow current reversed at 1 +/- 1.5 mV with symmetrical Cl(-) concentrations compared with 23.2 +/- 1.2 mV (n = 5) and -34.3 +/- 3.5 mV (n = 4) when external Cl(-) was substituted with either glutamate (86 mM) or I(-) (125 mM). Nifedipine (1 microM) blocked and BAY K 8644 enhanced I(Ca(L)), the slow-developing sustained current, and the tail current. The Cl(-) channel blocker anthracene-9-carboxylic acid (9-AC) reduced only the slowly developing inward and tail currents. Application of caffeine (10 mM) to voltage-clamped cells evoked currents that reversed close to the Cl(-) equilibrium potential and were sensitive to 9-AC. Small spontaneous transient depolarizations and larger action potentials were observed in current clamp, and these were blocked by 9-AC. Evoked action potentials were triphasic and had a prominent plateau phase that was selectively blocked by 9-AC. Similarly, fluid output was reduced by 9-AC in doubly cannulated segments of spontaneously pumping sheep lymphatics, suggesting that the Ca(2+)-activated Cl(-) current plays an important role in the electrical activity underlying spontaneous activity in this tissue.
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Toland HM, McCloskey KD, Thornbury KD, McHale NG, Hollywood MA. Ca(2+)-activated Cl(-) current in sheep lymphatic smooth muscle. Am J Physiol Cell Physiol 2000; 279:C1327-35. [PMID: 11029279 DOI: 10.1152/ajpcell.2000.279.5.c1327] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Freshly dispersed sheep mesenteric lymphatic smooth muscle cells were studied at 37 degrees C using the perforated patch-clamp technique with Cs(+)- and K(+)-filled pipettes. Depolarizing steps evoked currents that consisted of L-type Ca(2+) [I(Ca(L))] current and a slowly developing current. The slow current reversed at 1 +/- 1.5 mV with symmetrical Cl(-) concentrations compared with 23.2 +/- 1.2 mV (n = 5) and -34.3 +/- 3.5 mV (n = 4) when external Cl(-) was substituted with either glutamate (86 mM) or I(-) (125 mM). Nifedipine (1 microM) blocked and BAY K 8644 enhanced I(Ca(L)), the slow-developing sustained current, and the tail current. The Cl(-) channel blocker anthracene-9-carboxylic acid (9-AC) reduced only the slowly developing inward and tail currents. Application of caffeine (10 mM) to voltage-clamped cells evoked currents that reversed close to the Cl(-) equilibrium potential and were sensitive to 9-AC. Small spontaneous transient depolarizations and larger action potentials were observed in current clamp, and these were blocked by 9-AC. Evoked action potentials were triphasic and had a prominent plateau phase that was selectively blocked by 9-AC. Similarly, fluid output was reduced by 9-AC in doubly cannulated segments of spontaneously pumping sheep lymphatics, suggesting that the Ca(2+)-activated Cl(-) current plays an important role in the electrical activity underlying spontaneous activity in this tissue.
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Hollywood MA, McCloskey KD, McHale NG, Thornbury KD. Characterization of outward K(+) currents in isolated smooth muscle cells from sheep urethra. Am J Physiol Cell Physiol 2000; 279:C420-8. [PMID: 10913009 DOI: 10.1152/ajpcell.2000.279.2.c420] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The perforated-patch technique was used to measure membrane currents in smooth muscle cells from sheep urethra. Depolarizing pulses evoked large transient outward currents and several components of sustained current. The transient current and a component of sustained current were blocked by iberiotoxin, penitrem A, and nifedipine but were unaffected by apamin or 4-aminopyridine, suggesting that they were mediated by large-conductance Ca(2+)-activated K(+) (BK) channels. When the BK current was blocked by exposure to penitrem A (100 nM) and Ca(2+)-free bath solution, there remained a voltage-sensitive K(+) current that was moderately sensitive to blockade with tetraethylammonium (TEA; half-maximal effective dose = 3.0 +/- 0.8 mM) but not 4-aminopyridine. Penitrem A (100 nM) increased the spike amplitude and plateau potential in slow waves evoked in single cells, whereas addition of TEA (10 mM) further increased the plateau potential and duration. In conclusion, both Ca(2+)-activated and voltage-dependent K(+) currents were found in urethral myocytes. Both of these currents are capable of contributing to the slow wave in these cells, suggesting that they are likely to influence urethral tone under certain conditions.
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Sergeant GP, Hollywood MA, McCloskey KD, Thornbury KD, McHale NG. Specialised pacemaking cells in the rabbit urethra. J Physiol 2000; 526 Pt 2:359-66. [PMID: 10896724 PMCID: PMC2270007 DOI: 10.1111/j.1469-7793.2000.t01-2-00359.x] [Citation(s) in RCA: 196] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2000] [Accepted: 05/15/2000] [Indexed: 11/27/2022] Open
Abstract
1. Collagenase dispersal of strips of rabbit urethra yielded, in addition to normal spindle-shaped smooth muscle cells, a small proportion of branched cells which resembled the interstitial cells of Cajal dispersed from canine colon. These were clearly distinguishable from smooth muscle in their appearance under the phase-contrast microscope, their immunohistochemistry and their ultrastructure. They had abundant vimentin filaments but no myosin, a discontinuous basal lamina, sparse rough endoplasmic reticulum, many mitochondria and a well-developed smooth endoplasmic reticulum. 2. Interstitial cells were non-contractile but exhibited regular spontaneous depolarisations in current clamp. These could be increased in frequency by noradrenaline and blocked by perfusion with calcium-free solution. In voltage clamp they showed abundant calcium-activated chloride current and spontaneous transient inward currents which could be blocked by chloride channel blockers. 3. The majority of smooth muscle cells were vigorously contractile when stimulated but did not show spontaneous electrical activity in current clamp. In voltage clamp, smooth muscle cells showed very little calcium-activated chloride current. 4. We conclude that there are specialised pacemaking cells in the rabbit urethra that may be responsible for initiating the slow waves recorded from smooth muscle cells in the intact syncitium.
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McCloskey KD, Toland HM, Hollywood MA, Thornbury KD, McHale NG. Hyperpolarisation-activated inward current in isolated sheep mesenteric lymphatic smooth muscle. J Physiol 1999; 521 Pt 1:201-11. [PMID: 10562345 PMCID: PMC2269640 DOI: 10.1111/j.1469-7793.1999.00201.x] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/1999] [Accepted: 08/18/1999] [Indexed: 11/30/2022] Open
Abstract
1. Freshly isolated sheep lymphatic smooth muscle cells were studied using the perforated patch-clamp technique. Hyperpolarisation with constant-current pulses caused a time-dependent rectification evident as a depolarising 'sag' followed by an anode-break overshoot at the end of the pulse. Both sag and overshoot were blocked with 1 mM Cs+. 2. Cells were voltage clamped at -30 mV and stepped to -120 mV in 10 mV steps of 2 s duration. Steps negative to -60 mV evoked a slowly activating, non-inactivating inward current which increased in size and rate of activation with increasing hyperpolarisation. 3. The slowly activating current was reduced in Na+-free bathing solution but enhanced when the extracellular K+ concentration was increased to 60 mM. The current was significantly reduced by 1 mM Cs+ and 1 microM ZD7288 but not by 1.8 mM Ba2+. 4. The steady-state activation curve of the underlying conductance showed a threshold at -50 mV and half-maximal activation at -81 mV. Neither threshold nor half-maximal activation was significantly affected by increasing the external K+ concentration to 60 mM. 5. The frequency of spontaneous contractions and fluid propulsion in isolated cannulated segments of sheep mesenteric lymphatics were decreased by 1 mM Cs+ and by 1 microM ZD7288. 6. We conclude that sheep lymphatics have a hyperpolarisation-activated inward current similar to the If seen in sinoatrial node cells of the heart. Blockade of this current slows spontaneous pumping in intact lymphatic vessels suggesting that it is important in normal pacemaking.
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Glasgow PD, Hill ID, Baxter GD, Allen JM, Cramp AFL, Noble JG, Lowe AS, Walsh DM, Ryan S, O’Regan RG, McNicholas WT, Nolan P, Corkery PP, Leek BF, Carroll O, O’Cuinn G, Keane FM, Clarke CR, Robson T, McKeown SR, Moore SD, Hirst D, Sergeant GP, Hollywood MA, McHale NG, Thornbury KD, McCloskey KD, Magee PJ, Barnett CR, Downes CS, Humphrey R, McGuigan A, Hutchinson C, Hannigan BM, Saleshando G, O’Connor JJ, Curran BP, O’Neill LAJ, Kerrigan SW, Quinn M, Fitzerald DJ, Cox D, Dunne EM, Herron CE, O’Loinsigh E, Boland G, O’Boyle KM, Cullen VC, Mackarel AJ, O’Connor CM, Keenan AK, Cannon DM, McBean G, Baird AW, Frizelle HP, Moriarty DC, McGuire M, Bradford A, Ryan JP, Quinn T, Walker MD, Hirst DG, Hurley DA, McDonough SM, Moore A, Lagan KM, Dusoir AE, Wilson S, Sweeney C, Curtis TM, Scholfield CN, O’Connor S, Kilbride E, McLoughlin P, Gallagher CG, Harty HR, Gormley BA. Royal Academy of Medicine in Ireland Section of Biomedical Sciences. Ir J Med Sci 1999. [DOI: 10.1007/bf02944360] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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Abstract
We have studied the electrical and mechanical behaviour of two very different smooth muscle preparations, mesenteric lymphatic ducts and proximal urethra. These tissues generate different patterns of spontaneous contraction adapted to fulfil their contrasting functions. While lymphatics undergo regular phasic contractions and relaxations, suited to their role in propelling lymph, the urethra remains in a state of contracture to maintain urinary continence. The challenge is to understand how both of these achieve their respective roles. Interestingly, electrical activity of lymphatics resembles that in the heart in having a one to one relationship between the action potential and phasic contraction. Patch clamp studies have shown that lymphatic cells express 3 ionic currents that are not present in urethral cells, but are shared with cardiac muscle. These are, i) fast Na+ current, ii) T-type Ca2+ current and iii) a hyperpolarization-activated cation current, Ir. The fast Na+ current is ideally suited to the propagation of the action potential over large distances, as required by a vessel capable of generating a rapid well co-ordinated contraction along its length. The T-current and Ir, on the other hand, appear to be involved in electrical pacemaking as they are in the heart. The urethra does not usually undergo regular phasic contractions and it lacks these currents. Instead, urethral tone may depend on an interaction between L-type Ca2+ current and a large Ca(2+)-activated Cl- current. Activation of Cl- channels (perhaps by spontaneous release of Ca2+ from intracellular stores) would depolarize the membrane potential to within the 'window current' range for L-type Ca2+ channels and result in Ca2+ influx and contraction. This process may be maintained for a time by positive feedback whereby the influx of Ca2+ continues to activate the Cl- channels.
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Hollywood MA, Cotton KD, McHale NG, Thornbury KD. Enhancement of Ca2+-dependent outward current in sheep bladder myocytes by evans blue dye. Pflugers Arch 1998; 435:631-6. [PMID: 9479015 DOI: 10.1007/s004240050563] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Whole-cell and inside-out patch-clamp techniques were used to assess the action of a well-known dye, Evans blue, on membrane currents in bladder isolated smooth muscle cells from sheep. In whole cells Evans blue dose-dependently increased the outward current by up to fivefold. In contrast, Evans blue had no effect on inward Ca2+ current. The effect on outward current was abolished or reduced if the cells were bathed in Ca2+-free solution, iberiotoxin (5 x 10(-8) M), or charybdotoxin (5 x 10(-8) M), but was unaffected by externally applied caffeine (5 mM) or in cells exposed to heparin (1 mg/ml) via the patch pipette. In inside-out patches bathed in a Ca2+ concentration of 5 x 10(-7) M, Evans blue (10(-4) M) increased the open probability of large-conductance (298-pS) Ca2+-dependent K+ channels (BK channels), shifting the half maximal-activation voltage by -70 mV. We conclude that Evans blue dye acts as an opener of BK channels.
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Cotton KD, Hollywood MA, McHale NG, Thornbury KD. Ca2+ current and Ca(2+)-activated chloride current in isolated smooth muscle cells of the sheep urethra. J Physiol 1997; 505 ( Pt 1):121-31. [PMID: 9409476 PMCID: PMC1160098 DOI: 10.1111/j.1469-7793.1997.121bc.x] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
1. Isolated sheep urethral cells were studied using the perforated patch clamp technique (T = 37 degrees C). Depolarizing steps ranging from -40 to -10 mV evoked an inward current that peaked within 10 ms and a slower inward current. Stepping back to the holding potential of -80 mV evoked large inward tail currents. All three currents were abolished by nifedipine (1 microM). Substitution of external Ca2+ with Ba2+ resulted in potentiation of the fast inward current and blockade of the slow current and tails. 2. Changing the chloride equilibrium potential (ECl) from 0 to +27 mV shifted the reversal potential of the tail currents from 1 +/- 1 to 27 +/- 1 mV (number of cells, n = 5). Chloride channel blockers, niflumic acid (10 microM) and anthracene-9-carboxylic acid (9AC, 1 mM), reduced the slow current and tails suggesting that these were Ca(2+)-activated Cl- currents, ICl(Ca). 4. Caffeine (10 mM) induced currents that reversed at ECl and were blocked by niflumic acid (10 microM). 5. In current clamp mode, some cells developed spontaneous transient depolarizations (STDs) and action potentials. Short exposure to nifedipine blocked the action potentials and unmasked STDs. In contrast, 9AC and niflumic acid reduced the amplitude of the STDs and blocked the action potentials. 6. In conclusion, these cells have both L-type ICa and ICl(Ca). The former appears to be responsible for the upstroke of the action potential, while the latter may act as a pacemaker current.
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Cotton KD, Hollywood MA, McHale NG, Thornbury KD. Outward currents in smooth muscle cells isolated from sheep mesenteric lymphatics. J Physiol 1997; 503 ( Pt 1):1-11. [PMID: 9288669 PMCID: PMC1159881 DOI: 10.1111/j.1469-7793.1997.001bi.x] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
1. The patch-clamp technique was used to measure membrane currents in isolated smooth muscle cells dispersed from sheep mesenteric lymphatics. Depolarizing steps positive to -30 mV evoked rapid inward currents followed by noisy outward currents. 2. Nifedipine (1 microM) markedly reduced the outward current, while Bay K 8644 (1 microM) enhanced it. Up to 90% of the outward current was also blocked by iberiotoxin (Kd = 36 nM). 3. Large conductance (304 +/- 15 pS, 7 cells), Ca(2+)- and voltage-sensitive channels were observed during single-channel recordings on inside-out patches using symmetrical 140 mM K+ solutions (at 37 degrees C). The voltage required for half-maximal activation of the channels (V1/2) shifted in the hyperpolarizing direction by 146 mV per 10-fold increase in [Ca2+]i. 4. In whole-cell experiments a voltage-dependent outward current remained when the Ca(2+)-activated current was blocked with penitrem A (100 nM). This current activated at potentials positive to -20 mV and demonstrated the phenomenon of voltage-dependent inactivation (V1/2 = -41 +/- 2 mV, slope factor = 18 +/- 2 mV, 5 cells). 6. Tetraethylammonium (TEA; 30 mM) reduced the voltage-dependent current by 75% (Kd = 3.3 mM, 5 cells) while a maximal concentration of 4-aminopyridine (4-AP; 10 mM) blocked only 40% of the current. TEA alone had as much effect as TEA and 4-AP together, suggesting that there are at least two components to the voltage-sensitive K+ current. 7. These results suggest that lymphatic smooth muscle cells generate a Ca(2+)-activated current, largely mediated by large conductance Ca(2+)-activated K+ channels, and several components of voltage-dependent outward current which resemble 'delayed rectifier' currents in other smooth muscle preparations.
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Hollywood MA, Cotton KD, Thornbury KD, McHale NG. Tetrodotoxin-sensitive sodium current in sheep lymphatic smooth muscle. J Physiol 1997; 503 ( Pt 1):13-20. [PMID: 9288670 PMCID: PMC1159882 DOI: 10.1111/j.1469-7793.1997.013bi.x] [Citation(s) in RCA: 48] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
1. Fast inward currents were elicited in freshly isolated sheep lymphatic smooth muscle cells by depolarization from a holding potential of -80 mV using the whole-cell patch-clamp technique. The currents activated at voltages positive to -40 mV and peaked at 0 mV. 2. When sodium chloride in the bathing solution was replaced isosmotically with choline chloride inward currents were abolished at all potentials. 3. These currents were very sensitive to tetrodotoxin (TTX). Peak current was almost abolished at 1 microM with half-maximal inhibition at 17 nM. 4. Examination of the voltage dependence of steady state inactivation showed that more than 90% of the current was available at the normal resting potential of these cells (-60 mV). 5. The time course of recovery from inactivation was studied using a double-pulse protocol and showed that recovery was complete within 100 ms with a time constant of recovery of 20 ms. 6. Under current clamp, action potentials were elicited by depolarizing current pulses. These had a rapid upstroke and a short duration and could be blocked with 1 microM TTX. 7. Spontaneous contractions of isolated rings of sheep mesenteric lymphatic vessels were abolished or significantly depressed by 1 microM TTX.
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Mescall FM, Kane MT, Keyes WM, Quinlan LR, Hynes AC, Kane MT, Jordan FM, Hynes AC, McGarvey C, Kelly JP, O’Donnell JM, Kelliher P, O’Donnell JM, Cotton KD, Hollywood MA, Thornbury KD, McHale NG, Curran AK, O’Halloran KD, Bradford A, O’Rourke M, Docherty JR, Brady G, Lyall P, Felle P, Fanning P, O’Boyle KM, Cummins M, Naughton Y, Ryan MP, Clarke H, O’Connell C, McNamara B, Cuffe J, O’Sullivan G, Harvey B, Urbach V, Leguen I, Butt G, MacDonncha C, Watson AWS, Aherne AM, Vaughan CJ, Murphy MB, O’Connell DP, Walsh DE, Harvey BJ, Connor TJ, Kelly JP, Leonard BE, Wrynn AS, Earley B, Harkin AJ, Cassidy EM, O’Connor JJ, Brayden DJ, Dunne JF, Baird AW, McCole DF, Newsholme PN, Love GP, Keenan AK, Doolan CM, Higgins MA, Higgins T, Horwitz E, Reidy D, Redmond AM, McNamara MG, Maginn M, Tamate K, Charleton M, Leavy J, Nolan A, Egan D, Gosling JP, Fottrell PF, Kane M, Murphy N, Long M, Fitzgerald D, O’Fegan P, O’Doherty A, Forde T, Molloy G, Dawson MA, Maher M, Houghton JA, Mccole JC, Moran AP, O/rsmalley DT, Helander IM, Lindner B, Callaghan GA, Mcclorey MB, Hannigan BM, Gilmore WS, Allen JM, Whelton HJ, Dowdall D, Dawson M, Smith T, Whelton H, O≿doherty A, Mccusker J, Joyce KM, Mlay P, Leek BF, Clements BA, Grimes F, Walsh DM, Baxter GD, Toussi H, Lagan KM, Ashford R. Royal academy of medicine in ireland section of biomedical sciences. Ir J Med Sci 1996. [DOI: 10.1007/bf02940256] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Cotton KD, Hollywood MA, Thornbury KD, McHale NG. Effect of purinergic blockers on outward current in isolated smooth muscle cells of the sheep bladder. THE AMERICAN JOURNAL OF PHYSIOLOGY 1996; 270:C969-73. [PMID: 8638680 DOI: 10.1152/ajpcell.1996.270.3.c969] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
Freshly dispersed cells from sheep urinary bladder were voltage clamped using the whole cell and inside-out patch-clamp technique. Cibacron and Basilen blue increased outward current in a dose-dependent manner with a half-maximal response at 10(-5)M. Suramin, in concentrations to 10(-3)M, had no such effect. The Cibacron blue response was abolished in Ca2+ -free physiological salt solution, suggesting that it was acting on a Ca2+ -dependent current. Similarly, the Cibacron blue-sensitive current was significantly attenuated by charybdotoxin. Cibacron blue did not modulate inward current nor were its effects modified by caffeine or heparin, suggesting that its effect on outward current was not secondary to an increase in intracellular Ca2+. Application of 10(-4)M Cibacron blue to the inside membrane of excised patches caused a rapid increase in open probability of a large conductance (300 pS) K+ channel. These results suggest that Cibacron blue is a potent activator of a Ca2+ -dependent outward current in bladder smooth muscle cells in addition to its action as a purinergic blocker.
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Thornbury KD, Donaghy KM, Peake J. Characteristics of the NANC post-stimulus ('rebound') contraction of the urinary bladder neck muscle in sheep. Br J Pharmacol 1995; 116:2451-6. [PMID: 8581284 PMCID: PMC1909037 DOI: 10.1111/j.1476-5381.1995.tb15095.x] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
1. Strips of muscle from sheep bladder neck were set up for tension recording and subjected to electrical field stimulation (EFS) to stimulate their intramural nerves. 2. In the presence of atropine (1 microM) and guanethidine (1 microM), the response to 1 Hz EFS was biphasic, characterized by a relaxation during the stimulus period, followed by a post-stimulus contraction. A similar biphasic response was also seen following bolus application of nitric oxide (NO). 3. In the absence of atropine and guanethidine, the relaxations were masked by contractions during stimulation; however, the post-stimulus contraction were unaffected. L-NAME (100 microM) blocked the post-stimulus contractions and L-arginine (1 mM) restored them, suggesting that they were NO-mediated. 4. M&B 22948, a phosphodiesterase inhibitor, prolonged the relaxations and abolished the post-stimulus contractions. This suggests that rapid removal of cyclic GMP is required for post-stimulus contraction to occur. 5. When the number of pulses in the stimulus train was kept constant, the size of the post-stimulus contraction increased as the duration of the preceding period of stimulation increased. Maximal post-stimulus contractions were obtained following stimulation for > 40 s. 6. The L-channel antagonist, nifedipine (1 microM) and verapamil (1 microM), had little effect on the amplitude of the post-stimulus contractions. 7. In contrast, ryanodine-(8 microM) reduced the post-stimulus contractions by over 90%. Caffeine (20 mM) also abolished the post-stimulus contractions and cyclopiazonic acid (CPA, 10 microM) reduced them by 76%. However, in the presence of CPA a slower post-stimulus contraction developed. Nifedipine (1 microM) reduced this by 40%. 8. In conclusion, these results support a role for NO in the post-stimulus contraction of the sheep bladder neck muscle. The post-stimulus contraction depends more on release of intracellular Ca2+, than Ca2+ influx through L-type channels.
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Galligan E, Al-Assar O, McIntyre IA, McKeown SR, Hollywood MA, Thornbury KD, McHale NG, Keenan AK, Gierschik P, Nelson AA, McKenna PG, Barnett YA, Curran AK, O’Halloran KD, Bradford A, O’Haloran KD, Curran AK, Bradford A, Kent A, Keenan AK, Redrobe JP, Kelly JP, Leonard BE, Chambers PL, Ryan PM, Kelly JP, Leonard BE, Chambers PL, Redmond AM, Kelly JP, Leonard BE, McNamara MG, Kelly JP, Leonard BE, McShane AJ, Tobin E, Smith T, Fox GB, Kennedy N, Regan CM, O’Farrell FJ, Hannigan BM, Barnett YA, Walsh IK, Johnston SR, McKelvey-Martin VJ, McKeown SR, McAleer JJA, O’Halloran KD, Curran AK, Bradford A, Curran AK, O’Halloran KD, Bradford A, O’Regan RG, Kelly JP, Leonard BE, Mullen AM, Earley B, Leonard BE, O’Neill J, O’Connor JJ, Moynagh P, O’Neill LAJ, Kelly JA, Keenan AK, McHale NG, Gierschik P, Browne I, Gavin K, Docherty JR, Smith K, Gavin K, Docherty JR, Cawley T, Docherty JR, Geraghty J, Osborne H, Hyland PL, McKinney MW, McKenna PG, Barnett YA, McKeown SR, Hejmadi MV, McAleer JJA, Patterson LH, Sweeney M, McLoughlin P, O’Donnell MD, McGeeney KF, Cottell DC. Royal academy of medicine in ireland section of biomedical sciences. Ir J Med Sci 1995. [DOI: 10.1007/bf02967214] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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Cullinane A, Coca-Prados M, Harvey B, O’Reilly C, Ryan MP, Maguire D, O’Sullivan G, Harvey BJ, Gebruers EM, Hall WJ, Harris AM, O’Halloran KD, Curran AK, Bradford A, Bunting HE, McConaghy P, McLoughlin C, Sweeney D, Hardiman O, Grealy M, Sreenan JM, Gilmartin L, O’Cuinn G, Lawlor M, O’Boyle KM, Farrell CB, Foster NEL, Walsh DM, Baxter GD, Allen JM, Cawley T, Breslin E, Docherty JR, Hynes AC, Kane MT, Duffy C, Mohd Nor A, Johnson AH, Tomkin GH, Collins PB, Crónín DÓ, McCloskey S, Thornbury KD, O’Rourke M, Kearns S, Campion DP, Leek BF, Curran AK, Curran AK, O’Regan RG, McLaughlin N, Curran AK, Gaffney J, Edgell TA, Walker JM, MacSweeney CP, Faherty C, Kelly JP, Leonard BE, Earley B, O’Neill M, Reymann JM, Allain H, Caldwell M, Jennings M, Prosser E, Urbach V, Horwitz E, Horwitz ER, Presser E, Raffin JP, Thomas S, Egan DA, O’Farrell A. Royal academy of medicine in Ireland section of biomedical sciences Proceedings of Summer Meeting held June, 1994. Ir J Med Sci 1995. [DOI: 10.1007/bf02968123] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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Abstract
Spontaneous isometric contractions were measured in rings of sheep mesenteric lymphatics. Field stimulation at short pulse widths increased the frequency of spontaneous contractions and this response was blocked by 10(-7) M tetrodotoxin. The alpha-antagonists phentolamine, prazosin, and yohimbine failed to block the excitatory response in a dose of 10(-6) M. Exogenous noradrenaline (10(-6) M) increased the frequency and force of spontaneous contractions and this effect was blocked by a 10(-6) M phentolamine. Atropine 10(-6) M failed to block the excitatory response to field stimulation. alpha beta-methylene ATP caused an intense transient excitatory effect followed by recovery to a frequency level just above that of control but the excitatory effect of field stimulation was not blocked in these desensitized vessels. When vessels were exposed to a mixture of 10(-4) M noradrenaline and 10(-5) M phentolamine field stimulation did not further increase the frequency of spontaneous contractions. These results demonstrate that the innervation of sheep mesenteric lymphatics is different from that of bovine mesenteric lymphatics. The identity of the transmitter is as yet unknown but it does not appear to be ATP nor is it noradrenaline acting on postsynaptic alpha-receptors.
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MacDermott M, Doolan C, Keenan AK, Twomey C, Doyle M, Kirby F, McDonald N, McShane AJ, Deasy PB, Boles MG, Donnellan MF, Hilton AK, Wall M, Horan R, Houghton JA, Southey A, O’Connor CM, Fitzgerald MX, Scott TG, Fitzgerald MF, Hegarty V, Keane CT, Coakley D, Moran AP, Walsh EJ, Hickey K, Monkhouse S, Folan-Curran J, Caulfield B, Garrett M, Lowe AS, Baxter GD, Walsh DM, Allen JM, Lawlor M, Farrelly C, O’Boyle KM, O’Connell A, Earley B, Leonard BE, Han B, Kelly JP, O’Donnell JM, O’Neill M, Song C, Sherphard RA, Leslie JC, Toal L, Wedlock P, Yeruva N, O’Donovan DJ, Craig JA, Fegan JA, Kent A, Atkinson PRT, Peake J, Thornbury KD, Campion DP, Leek BF, Bird J, Carroll C. Royal academy of medicine in Ireland section of biomedical sciences. Ir J Med Sci 1993. [DOI: 10.1007/bf02942170] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Thornbury KD, Harty HR, McGeown JG, McHale NG. Mesenteric lymph flow responses to splanchnic nerve stimulation in sheep. THE AMERICAN JOURNAL OF PHYSIOLOGY 1993; 264:H604-10. [PMID: 8447473 DOI: 10.1152/ajpheart.1993.264.2.h604] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
The main mesenteric lymph duct was cannulated in halothane-anesthetized sheep, and continuous recordings were made of lymph flow, lymphatic pressure fluctuations, and arterial pressure. Stimulation of the left greater splanchnic nerve at frequencies of 1, 4, and 10 Hz caused lymph flow to increase by 30 +/- 9, 74 +/- 19, and 80 +/- 21%, respectively. Lymphatic contraction frequency and mean arterial pressure showed graded increases in response to increasing stimulus frequencies. These responses were reduced after intravenous infusion of phentolamine, suggesting that they were mediated by alpha-adrenoceptors. Lymph protein concentration remained unchanged during stimulation, suggesting that lymph formation in the nodes was not responsible for the increased lymph flow. The lymph flow response during 20 min of stimulation was biphasic, showing an initial transient increase followed by a depression to 45% of control. It is concluded that the initial increase in flow may be explained by stimulation of the lymphatic pump by nerves and/or circulating catecholamines, while the subsequent decrease reflected a reduction in lymph formation.
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Thornbury KD, Ward SM, Sanders KM. Participation of fast-activating, voltage-dependent K currents in electrical slow waves of colonic circular muscle. THE AMERICAN JOURNAL OF PHYSIOLOGY 1992; 263:C226-36. [PMID: 1636679 DOI: 10.1152/ajpcell.1992.263.1.c226] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The plateau phase of electrical slow waves in phasic gastrointestinal muscles is critical for excitation-contraction coupling. The plateau appears to depend upon a balance between inward Ca2+ current and outward K+ currents that is sustained for several seconds. Voltage-dependent, non-Ca(2+)-dependent K currents were studied in canine colonic circular muscle cells using the whole cell patch-clamp technique. At room temperature, depolarization activated a slow outward current that showed little inactivation during 500 ms. Increasing the temperature to 37 degrees C significantly increased the rate of activation of voltage-dependent outward current. The onset of the outward current overlapped the transient inward Ca2+ current, suggesting that this K current may act as a brake on the upstroke depolarization of electrical slow waves in intact muscles. Voltage-dependent outward current was sustained for the duration of test pulses. This current balanced the sustained inward current that was also activated at physiological test potentials. The outward current evoked by test pulses positive to -20 mV inactivated by at least 50% within 500 ms. Half inactivation occurred at -36 mV. Voltage-dependent K current was reduced by 4-aminopyridine (4-AP; 1-5 mM), but difference currents obtained by subtracting currents elicited from holding potentials of -45 mV from currents obtained from holding potentials of -100 mV were not affected by 4-AP (1 mM). Studies were also performed on intact muscles to test the effects of 4-AP on electrical slow waves. 4-AP increased the amplitude and rate of rise of the upstroke potential and increased the amplitude and prolonged the plateau phase of slow waves. These data suggest that a rapidly activating, inactivating, voltage-dependent K current participates in electrical slow waves of colonic circular smooth muscles.
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Bourke W, O’Connor C, Fitzgerald MX, McConnell TJ, Kent A, Redmond EM, Keenan AK, Smyth EM, Shanahan R, O’Donnell N, O’Connor CM, Kelly V, Barry-Kinsella C, Sharma SC, Cottrell E, Harrison RF, Sheppard BL, Bonnar J, McNally O, Hannigan B, Allen JM, Feely J, Buggy D, Barry M, Keeling PWN, Weir DG, Breathnach A, Keogh B, Cooke T, Murphy J, O’Sullivan C, Walsh M, Tyrrell J, Bergin C, Colgan M, Moore D, Shanik DG, Cooke T, Southey A, Costello E, Jehn B, Marti R, Deane R, Thornton F, Jaggi R, Martin F, Armstrong C, Mannion D, Feely T, Fitzpatrick G, McCormack PME, O’Reilly E, Walsh JB, Coakley D, Stinson JC, Murphy CM, Andrews JF, Tomkin GH, Howe JP, Fogarty DJ, Manahan-Vaughan D, Rowan MJ, Anwyl R, Thornbury KD, Ward SM, Sanders KM, Murnin M, Guthrie DJS, Irvine GB, Doyle E, Regan CM, Bannigan J, Giles J, Adebayo GI, Deasy PB, Omara AAM, Lambert MB, Shields TD, O’Kane S, Leckey D, Gilmore WS, Hannigan BM, McKeogh D, Bradford A, O’Regan RG, Nolan P, McEvoy F, Edgell T, Webbon P, Creighton-Kempsford L, Gaffney PJ, O’Donnell MD, McGeeney KF, Breslin E, Smith K, Docherty JR, Adams N, Ravey J, Bell AJ, Tong KK, Strain JJ, Walsh DM, Baxter GD, Mokhtar B, Victory R, Bergin D, Cooney C, Staunton M, Fitzgerald J, Gardiner J, Blunnie W, Smith J, Magee O, Lowe D, Robinson R, Magner J, Eustace P, Martyn CJ, Cooney CM, Adams H, Lyons JB, Blunnie WP, Moriarty DC. Royal academy of medicine in ireland section of biological sciences. Ir J Med Sci 1992. [DOI: 10.1007/bf02942159] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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Thornbury KD, Ward SM, Sanders KM. Outward currents in longitudinal colonic muscle cells contribute to spiking electrical behavior. THE AMERICAN JOURNAL OF PHYSIOLOGY 1992; 263:C237-45. [PMID: 1378997 DOI: 10.1152/ajpcell.1992.263.1.c237] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Electrical events in longitudinal and circular muscles of the colon are different. Longitudinal muscles generate action potentials superimposed upon small depolarizations termed myenteric potential oscillations and circular muscles generate slow wave events that persist for several seconds. Differences between circular and longitudinal muscles may be related to the potassium channels these cells express. We have studied Ca(2+)-dependent and voltage-dependent K currents of isolated longitudinal cells with the whole cell patch-clamp technique. Test depolarizations positive to -40 mV yielded a transient inward current followed by a large sustained outward current. Blockade of the inward Ca2+ current reduced the amplitude of the outward current. Outward current was also reduced by tetraethylammonium (TEA; 1 mM), suggesting that a component of the outward current is Ca2+ dependent. After blockade of the Ca(2+)-dependent outward current, a voltage- and time-dependent component of outward current remained. The activation and inactivation properties and sensitivity to TEA and 4-aminopyridine (4-AP) were characterized. The voltage-dependent outward current in longitudinal cells had different properties than the voltage-dependent K currents in circular muscle cells (i.e., more negative inactivation, less sensitivity to 4-AP). TEA (1-5 mM) increased the amplitude and frequency of action potentials in intact longitudinal muscles; 4-AP (1 mM) had little effect on electrical activity of longitudinal muscles. The data suggest that differences in electrical behavior of the 2 muscle layers may be related to the expression of different species of K channels.
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Ward SM, Dalziel HH, Thornbury KD, Westfall DP, Sanders KM. Nonadrenergic, noncholinergic inhibition and rebound excitation in canine colon depend on nitric oxide. THE AMERICAN JOURNAL OF PHYSIOLOGY 1992; 262:G237-43. [PMID: 1539659 DOI: 10.1152/ajpgi.1992.262.2.g237] [Citation(s) in RCA: 28] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Nonadrenergic, noncholinergic (NANC) nerves regulate slow waves along the submucosal border of the canine proximal colon. Experiments were performed to determine the role of nitric oxide (NO) in NANC responses. NANC responses are characterized by hyperpolarization and reduction in slow-wave amplitude and duration during the period of stimulation. This is followed by a "rebound" excitation (increase in amplitude and duration) of the slow wave immediately after the stimulus. These responses were blocked by L-arginine methyl ester (L-NAME), an inhibitor of nitric oxide synthase and by tetrodotoxin (TTX). Exogenous NO mimicked NANC responses, including the poststimulus rebound excitation. Responses to NO were unaffected by L-NAME or TTX. Responses to NANC nerve stimulation and NO were blocked by oxyhemoglobin but not by methemoglobin. Rebound excitation was reduced by pretreatment with indomethacin, suggesting that an eicosanoid may mediate this phase of NANC responses. Taken together, these data suggest that NO mediates NANC nerve responses in the proximal colon. NO appears to directly cause the inhibitory response, but the rebound response may depend on release of an eicosanoid.
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Sanders KM, Ward SM, Thornbury KD, Dalziel HH, Westfall DP, Carl A. Nitric oxide as a non-adrenergic, non-cholinergic neurotransmitter in the gastrointestinal tract. JAPANESE JOURNAL OF PHARMACOLOGY 1992; 58 Suppl 2:220P-225P. [PMID: 1354765] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Grants] [Subscribe] [Scholar Register] [Indexed: 03/25/2023]
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