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ANDO T, KUME H, URATA Y, TAKAGI K. Effects of JTV-506, a new K+
channel activator, on airway smooth muscle contraction and systemic blood pressure. Clin Exp Allergy 2006. [DOI: 10.1111/j.1365-2222.1997.tb01200.x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Martin TJ, Broadley KJ. Contractile responses to adenosine, R-PIA and ovalbumen in passively sensitized guinea-pig isolated airways. Br J Pharmacol 2002; 137:729-38. [PMID: 12411402 PMCID: PMC1573546 DOI: 10.1038/sj.bjp.0704902] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
1. Responses to adenosine, R-PIA and ovalbumen were examined in guinea-pig isolated superfused tracheal spirals to determine the effects of passive sensitization by overnight incubation in serum from ovalbumen (OA)-sensitized or non-sensitized guinea-pigs. 2. Tissues incubated with serum from non-sensitized and OA-sensitized guinea-pigs contracted (0.07+/-0.02 and 0.04+/-0.01 g, respectively) to adenosine (300 micro M) whereas non-incubated or Krebs-incubated tissues produced no contractions to adenosine or ovalbumen (10 micro g). Ovalbumen caused substantial contractions (0.40+/-0.09 g) after OA-sensitized serum incubation and significantly (P<0.05) smaller contractions (0.08+/-0.03 g) after non-sensitized serum incubation. Tracheae from guinea-pigs actively sensitized to ovalbumen 14-21 days beforehand also contracted to adenosine, R-PIA (3 micro M) and ovalbumen. 3. The A(1)/A(2) adenosine receptor antagonist, 8-phenyltheophylline (8-PT, 3 micro M), failed to antagonize these contractions, suggesting that A(1)/A(2) adenosine receptors were not involved. 4. Unlike adenosine, R-PIA (3 micro M) produced contractions in non-incubated (0.23+/-0.04 g) or Krebs-incubated (0.15+/-0.04 g) tracheae, as well as after passive and active sensitization. None of these responses were blocked by 8-PT. 5. The A(3) receptor agonist, IB-MECA, in the presence of 8-PT produced small contractions in passively sensitized tracheae (10 micro M, 0.02+/-0.003 g) and, in larger doses (100 micro M and 1 mM), contracted actively sensitized tracheae. 6. In actively sensitized trachea, the A(3) receptor antagonist, MRS-1220 (100 nM), significantly (P<0.05) attenuated adenosine contractions in the presence of 8-PT from 0.23+/-0.07 g to 0.07+/-0.03 g. 7. These results show that passive, like active sensitization, reveals bronchoconstrictions to adenosine of isolated tracheae. The insensitivity to 8-PT blockade, the antagonism by MRS-1220, and the fact that the A(3) receptor agonist, IB-MECA, mimics this response, suggest involvement of A(3) receptors. R-PIA, however, has a different profile of adenosine receptor activity.
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Affiliation(s)
- Timothy J Martin
- Department of Pharmacology, Welsh School of Pharmacy, Cardiff University, Cathays Park, Cardiff, CF10 3XF, U.K
| | - Kenneth J Broadley
- Department of Pharmacology, Welsh School of Pharmacy, Cardiff University, Cathays Park, Cardiff, CF10 3XF, U.K
- Author for correspondence:
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Abstract
Bronchial hyperresponsiveness (BHR), the increased sensitivity to a wide variety of stimuli that narrow the airways, is a central abnormality in patients with asthma, and is frequently observed in patients with chronic obstructive pulmonary disease. In the study of the underlying mechanisms of BHR, various animal models have been employed, using methods of active and passive immunization. These studies have led to a changed understanding of smooth muscle hyperreactivity, questioning both the past paradigm of altered neural activity and the modern concepts of inflammation as the single most factor determining BHR, and emphasizing the particular importance of the end organ- the smooth muscle cell. More recently, passive sensitization of human airways has been used by several investigators to describe the mechanisms of allergic sensitization and to study the role of functional abnormalities of human airway smooth muscle, which may represent the key to understanding human BHR, and thus lead to novel treatment approaches for the future.
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Affiliation(s)
- K F Rabe
- Krankenhaus Grosshansdorf, Zentrum fur Pneumologie und Thoraxchirurgie, LVA Freie und Hansestadt Hamburg, Grosshansdorf, Germany.
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Li L, Paakkari I, Vapaatalo H. Effects of K+ channel inhibitors on the basal tone and KCl- or methacholine-induced contraction of mouse trachea. Eur J Pharmacol 1998; 346:255-60. [PMID: 9652367 DOI: 10.1016/s0014-2999(98)00074-0] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
The present study examined the effects of K+ channel inhibitors on the basal tone and on KCl- or methacholine-induced contraction of the mouse-isolated trachea. Glibenclamide and iberiotoxin, procaine, quinine and tetraethylammonium did not induce any contraction of the indomethacin-treated mouse trachea. 4-Aminopyridine induced concentration-dependent contraction. This action of 4-aminopyridine was abolished by atropine and reduced by tetrodotoxin and nifedipine. Glibenclamide failed to modify KCl- or methacholine-induced contraction. Iberiotoxin and 4-aminopyridine potentiated KCl- and methacholine-induced contractions. Nifedipine, procaine, quinine and tetraethylammonium inhibited KCl- and methacholine-induced contractions. These data suggest that the closure of large Ca2+-dependent K+ channels can potentiate KCI- and methacholine-induced contraction. The effects of 4-aminopyridine on the mouse trachea reflect chiefly activation of muscarinic receptors. Procaine, quinine and tetraethylammonium inhibit depolarization-induced and receptor-mediated contractions of the mouse-isolated trachea.
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Affiliation(s)
- L Li
- Institute of Biomedicine, Department of Pharmacology and Toxicology, University of Helsinki, Finland
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Mitchell RW, Rabe KF, Magnussen H, Leff AR. Passive sensitization of human airways induces myogenic contractile responses in vitro. J Appl Physiol (1985) 1997; 83:1276-81. [PMID: 9338437 DOI: 10.1152/jappl.1997.83.4.1276] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
We assessed effects of passive sensitization on human bronchial smooth muscle (BSM) response to mechanical stretching in vitro. Bronchial rings were sham (control) or passively sensitized overnight by using sera from donors demonstrating sensitivity to Dermatophagoides farinae and having immunoglobulin E (IgE) concentrations of 2,600 +/- 200 U/ml. Tissues were fixed isometrically to force transducers to measure responses to electrical field stimulation (EFS) and quick stretch (QS). The myogenic response to QS was normalized to the maximal response to EFS (%EFS). The myogenic response of sensitized BSM was 47.9 +/- 10.9 %EFS to a QS of approximately 6.5% optimal length (Lo); sham-sensitized tissues had a myogenic response of 13.5 +/- 6.4 %EFS (P = 0.012 vs. passively sensitized). A QS of approximately 13% Lo in sensitized BSM caused a response of 82.8 +/- 20.9 %EFS; sham-sensitized tissues developed a response of 38.2 +/- 17.3 %EFS (P = 0.004). BSM incubated with serum from nonallergic donors did not demonstrate increased QS response (4.6 +/- 1.4 %EFS, P = not significant vs. tissue exposed to atopic sera). However, tissues incubated in sera from nonatopic donors supplemented with hapten-specific chimeric IgE (JW8) demonstrated augmented myogenic response to QS of approximately 6.5% Lo (21.9 +/- 6.2 %EFS, P = 0. 027 vs. nonatopic sera alone). We demonstrate that passive sensitization of human BSM preparations causes induction and augmentation of myogenic contractions to QS; this hyperresponsiveness corresponds to the IgE concentration in sensitizing sera.
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Affiliation(s)
- R W Mitchell
- Asthma, Allergy, and Immunological Disease Research Center, The University of Chicago, Chicago, Illinois 60637, USA
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Shieh CC, Petrini M, Dwyer T, Farley J. Effects of Elevated Cytosolic Calcium on ACh-Induced Swine Tracheal Smooth Muscle Contraction. J Biomed Sci 1996; 3:348-358. [PMID: 11725117 DOI: 10.1007/bf02257965] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
Abstract
Increased intracellular calcium concentration ([Ca(2+)](i)) is required for smooth muscle contraction. In tracheal and other tonic smooth muscles, contraction and elevated [Ca(2+)](i) are maintained as long as an agonist is present. To evaluate the physiological role of steady-state increases in Ca(2+) on tension maintenance, [Ca(2+)](i) was elevated using ionomycin, a Ca(2+) ionophore or charybdotoxin, a large-conductance calcium-activated potassium channel (K(Ca)) blocker prior to or during exposure of tracheal smooth muscle strips to ACh (10(-9) to 10(-4) M). Ionomycin (5 &mgr;M) in resting muscles induced increases in [Ca(2+)](i) to 500 +/- 230 nM and small increases in force of 2.6 +/- 2.3 N/cm(2). This tension is only 10% of the maximal tension induced by ACh. Charybdotoxin had no effect on [Ca(2+)](i) or tension in resting muscle. After pretreatment of muscle with ionomycin, the concentration-response relationship for ACh-induced changes in tension shifted to the left (EC(50) = 0.07 +/- 0.05 &mgr;M ionomycin; 0.17 +/- 0.07 &mgr;M, control, p < 0.05). When applied to the muscles during steady-state responses to submaximal concentrations of ACh, both ionomycin and charybdotoxin induced further increases in tension. The same magnitude increase in tension occurs after ionomycin and charybdotoxin treatment, even though the increase in [Ca(2+)](i) induced by charybdotoxin is much smaller than that induced by ionomycin. We conclude that the resting muscle is much less sensitive to elevation of [Ca(2+)](i) when compared to muscles stimulated with ACh. Steady-state [Ca(2+)](i) limits tension development induced by submaximal concentrations of ACh. The activity of K(Ca) moderates the response of the muscle to ACh at concentrations less than 1 &mgr;M. Copyright 1996 S. Karger AG, Basel
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Affiliation(s)
- C.-C. Shieh
- Department of Pharmacology and Toxicology, University of Mississippi Medical Center, Jackson, Miss., USA
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Thulesius O, Mustafa S. Stretch-induced myogenic responses of airways after histamine and carbachol. CLINICAL PHYSIOLOGY (OXFORD, ENGLAND) 1994; 14:135-43. [PMID: 8205744 DOI: 10.1111/j.1475-097x.1994.tb00499.x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
The purpose of the study described here was to determine the possible role of a myogenic response of bronchial smooth muscle in deep inspiration (DI)-induced bronchoconstriction. Model experiments were performed on sheep tracheal strips. The effect of sudden stepwise elongation on isometric tension of tracheal muscle was studied in the absence and presence of the bronchoconstrictors carbachol (10(-8) M) and histamine (10(-4) M). In control strips tension increased rapidly with stretch and was followed by stress relaxation which corresponds to creep or bronchial dilatation. In histamine- and carbachol-treated strips a reactive contraction with a rhythmic pattern interrupted the process of stress relaxation. These responses appeared after only 20% elongation and were characteristic of a myogenic contraction which in the in vivo situation would correspond to a bronchoconstriction. These findings are interpreted as a functional transformation of multiple- to single-unit smooth muscle due to the influence of carbachol and histamine. This suggests that stretching (DI) of bronchial smooth muscle in the presence of carbachol and histamine induces a protracted myogenic contraction, which may explain bronchoconstriction after DI in severe asthma.
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Affiliation(s)
- O Thulesius
- Department of Clinical Physiology, University Hospital Linköping, Sweden
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Fleischmann BK, Washabau RJ, Kotlikoff MI. Control of resting membrane potential by delayed rectifier potassium currents in ferret airway smooth muscle cells. J Physiol 1993; 469:625-38. [PMID: 8271220 PMCID: PMC1143891 DOI: 10.1113/jphysiol.1993.sp019834] [Citation(s) in RCA: 68] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
1. In order to determine the physiological role of specific potassium currents in airway smooth muscle, potassium currents were measured in freshly dissociated ferret trachealis cells using the nystatin-permeabilized, whole-cell method, at 35 degrees C. 2. The magnitude of the outward currents was markedly increased as bath temperature was increased from 22 to 35 degrees C. This increase was primarily due to the increase in maximum potassium conductance (gK,max), although there was also a small leftward shift in the relationship between gK and voltage at higher temperatures. The maximum conductance and the kinetics of current activation and inactivation were also temperature dependent. At 35 degrees C, gating of the current was steeply voltage dependent between -40 and 0 mV. Current activation was well fitted by fourth-order kinetics; the mean time constants of activation (30 mV clamp step) were 1.09 +/- 0.17 and 1.96 +/- 0.27 ms at 35 and 22 degrees C, respectively. 3. Outward currents using the nystatin method were qualitatively similar to delayed rectifier currents recorded in dialysed cells with high calcium buffering capacity solutions. 4-Aminopyridine (4-AP; 2 mM), a specific blocker of delayed rectifier potassium channels in this tissue, inhibited over 80% of the outward current evoked by voltage-clamp steps to between -10 and +20 mV (n = 6). Less than 5% of the outward current was blocked over the same voltage range by charybdotoxin (100 nM; n = 15), a specific antagonist of large-conductance, calcium-activated potassium channels in this tissue. 4. The degree to which delayed rectifier and calcium-activated potassium conductances control resting membrane potential was examined in current-clamp experiments. The resting membrane potential of current clamped cells was -33.6 +/- 1.0 mV (n = 62). Application of 4-AP (2 mM) resulted in a 14.4 +/- 1.0 mV depolarization (n = 8) and an increase in input resistance. Charybdotoxin (100 nM) had no effect on resting membrane potential (n = 6). 5. Force measurements were made in isolated strips of trachealis muscle to determine the effect of pharmacological blockade of individual potassium conductances on resting tone. In the presence of tetrodotoxin (1 microM) and atropine (1 microM), 4-AP increased baseline tension in a dose-dependent manner, with an EC50 of 1.8 mM (n = 13); application of 5 mM 4-AP increased tone to 86.8 +/- 8.1% of that produced by 1 microM methacholine, and this tone was almost completely inhibited by nifedipine (1 microM).(ABSTRACT TRUNCATED AT 400 WORDS)
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Affiliation(s)
- B K Fleischmann
- Department of Animal Biology, School of Veterinary Medicine, University of Pennsylvania, Philadelphia 19104-6046
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Stephens NL, Jiang H, Halayko A. Role of airway smooth muscle in asthma: possible relation to the neuroendocrine system. Anat Rec (Hoboken) 1993; 236:152-63; discussion 163-7. [PMID: 8507002 DOI: 10.1002/ar.1092360119] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Though not yet firmly established, it appears likely that the neuroendocrine system (NES) regulates airway smooth muscle function. As it is the latter which is altered in asthma, the importance of the role of the NES in this disease is clear. The fact that transmitters from the NE cells are released from their basal aspect, and are in close proximity to the subjacent airway smooth muscle, further indicates an interaction. The question then arises as to what are the experimental desiderata for conducting studies of the ASM. These should constitute what Sergei Sorokin has called the "Koch's postulates of airway smooth muscle research." As human tissues from asthmatics are difficult to obtain, animal models have been developed. The requirements are that, in these animals, the allergy be IgE based, that a congenital or familial factor be operative, that a noncholinergic nonadrenergic inhibitory system be a component of the neural regulatory system, and that the antigen for immunization be of a type commonly found in human asthmatics. Ideally, evidence of clinical asthma and exercise-induced asthma and nocturnal attacks should also be present. Unfortunately, no ideal animal models exist and one cannot talk about asthmatic animals, but only of animals with allergic bronchospasm. If in vitro research is to be conducted, there are additional requirements. The tissue should be from a relevant location. The tracheal smooth muscle which has been the favorite, purely because of its convenience, is not a good model. For the early asthmatic attack, central bronchi (3-5 mm diameter) should be used. Muscle strips obtained from them should be parallel-fibred and the cartilage plaques should be carefully dissected away, otherwise they contribute unwanted frictional forces when velocity is measured. Care should be taken to ensure that the epithelial cell layer is intact, as evidence indicates that it may regulate airway muscle function, though this has not been established for all the animal species used in asthma research. The isolated muscle strip should be in a steady state, particularly with respect to the functional variable under study, before definitive data are collected. Most importantly, it is shortening capacity that must be studied, as this is the in vitro analogue to in vivo narrowing of airways. Isometric force development provides information about wall stiffness and is of very little relevance to the elucidation of the mechanism of bronchospasm.(ABSTRACT TRUNCATED AT 400 WORDS)
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12
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Abstract
Potassium channels are an important determinant of smooth muscle excitability and force generation. Two potassium channels have been fully described in airway smooth muscle: large conductance, calcium-activated potassium channels and voltage-dependent delayed rectifier channels. This article will review the biophysics and pharmacology of these channels and discuss what is currently known with respect to their regulation and physiological significance.
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Affiliation(s)
- M I Kotlikoff
- Department of Animal Biology, School of Veterinary Medicine, University of Pennsylvania, Philadelphia 19104-6046
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Boyle JP, Tomasic M, Kotlikoff MI. Delayed rectifier potassium channels in canine and porcine airway smooth muscle cells. J Physiol 1992; 447:329-50. [PMID: 1593449 PMCID: PMC1176039 DOI: 10.1113/jphysiol.1992.sp019005] [Citation(s) in RCA: 67] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
1. In order to define the ion channels underlying the inactivating, calcium-insensitive current in airway smooth muscle cells, unitary potassium currents were recorded from canine and porcine trachealis cells, and compared with macroscopic currents. On-cell and inside-out single-channel currents were compared with whole-cell recordings made in dialysed cells. 2. Depolarizing voltage steps evoked outward unitary currents. In addition to a large conductance, calcium-activated potassium channel (KCa), a lower conductance potassium channel was identified. This channel has a conductance of 12.7 pS (on-cell; 1 mM-K+ in the pipette). 3. The lower conductance channel (Kdr) was not sensitive to cytosolic Ca2+ concentration and unitary current openings occurred following a delay after the voltage step. The time course of activation of the current composed of averaged single-channel events was very similar to that of the whole-cell, delayed rectifier potassium current (IdK), recorded under conditions of low intracellular calcium (Kotlikoff, 1990). 4. Kdr channels also inactivated with kinetics similar to those of the macroscopic current. Averaged single-channel records revealed a current that inactivated with kinetics that could be described by two exponentials (tau 1 = 0.14 s, tau 2 = 1.1 s; at 5 mV). These values corresponded well with previously determined values for time-dependent inactivation of IdK. Inactivation of Kdr channels was markedly voltage dependent, and was well fitted by a Boltzmann equation with V50 = -53 mV; this was similar to measurements of the macroscopic current, although the V50 value was shifted to more positive potentials in whole-cell measurements. When only the inactivating component of the macroscopic current was considered, the voltage dependence of inactivation of the single-channel current and macroscopic current were quite similar. 5. Single-channel kinetics indicated that Kdr channels occupy one open and two closed states. The mean open time was 1.7 ms. Inactivation results in a prominent increase in the long closed time, with little effect on the mean open time or short closed time. 6. The Kdr channel was not blocked by tetraethylammonium (TEA; 1 mM), charybdotoxin (ChTX; 100 nM) or glibenclamide (20 microM), but was blocked by 4-aminopyridine (4-AP; 1 mM). Similarly, 4-AP blocked the inactivating component of the macroscopic current, but a non-inactivating current remained. KCa currents were blocked by TEA (0.5-1 mM) and charybdotoxin (40 nM), but were insensitive to to 4-AP (1 mM) and glibenclamide (20 microM).(ABSTRACT TRUNCATED AT 400 WORDS)
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Affiliation(s)
- J P Boyle
- Department of Animal Biology, School of Veterinary Medicine, University of Pennsylvania, Philadelphia 19104-6046
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Green KA, Foster RW, Small RC. A patch-clamp study of K(+)-channel activity in bovine isolated tracheal smooth muscle cells. Br J Pharmacol 1991; 102:871-8. [PMID: 1713110 PMCID: PMC1917987 DOI: 10.1111/j.1476-5381.1991.tb12269.x] [Citation(s) in RCA: 44] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
1. Single smooth muscle cells were isolated from bovine trachealis by enzymic digestion. The properties of large conductance plasmalemmal K(+)-channels in these cells were studied by the patch-clamp recording technique. 2. Recordings were made from inside-out plasmalemmal patches when [K+] was symmetrically high (140 mM) and when [Ca2+] on the cytosolic side of the patch was varied from nominally zero to 10 microM. Large unitary currents of both Ca(2+)-dependent and -independent types were observed. Measured between + 20 and + 40 mV, the slope conductances of the channels carrying these currents were 249 +/- 18 pS and 268 +/- 14 pS respectively. 3. Lowering [K+] on the cytosolic side of the patches from 140 to 6 mM, shifted the reversal potentials of the two types of unitary current from approximately zero to much greater than + 40 mV, suggesting that both currents were carried by K(+)-channels. 4. The Ca(2+)-dependent and -independent K(+)-channels detected in inside-out plasmalemmal patches could also be distinguished on the basis of their sensitivity to inhibitors (tetraethylammonium (TEA), 1-10 mM; Cs+, 10 mM; Ba2+, 1-10 mM; quinidine, 100 microM) applied to the cytosolic surface of the patches. 5. Recordings were made from outside-out plasmalemmal patches when [K+] was symmetrically high (140 mM) and when [Ca2+] on the cytosolic side of the patch was varied from nominally zero to 1 microM. Ca(2+)-dependent unitary currents were observed and the slope conductance of the channel carrying these currents was 229 +/- 5 pS. 6. Activity of the Ca2+-dependent K+-channel detected in outside-out patches could be inhibited by application of TEA (1 mM), Cs+ (10mM), Ba2(+210mM) or quinidine (100 microM) to the external surface of the patch. 4-Aminopyridine (4-AP; 1 mM) was ineffective as an inhibitor. 7. The activity of the Ca2+-dependent K+-channel recorded from outside-out patches was reversibly inhibited by charybdotoxin (100 nM). 8. When whole-cell recording was performed, the application of a depolarizing voltage ramp evoked outward current which was dependent on the [Ca2 +] in the recording pipette and which could be reversibly inhibited by charybdotoxin (50 nM-I microM) applied to the external surface of the cell.9. We conclude that bovine trachealis cells are richly endowed with charybdotoxin-sensitive, large conductance, Ca2 +-dependent K+-channels. These channels carry most of the outward current evoked by a depolarizing ramp and could play a major role in determining the outward rectifying properties of the trachealis cells. The role of the large Ca2 + -independent K+ -channels remains unclear.
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Affiliation(s)
- K A Green
- Department of Physiological Sciences, University of Manchester
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Chand N, Diamantis W, Sofia RD. Induction of non-specific airway hyperreactivity by potassium channel blockade in rat isolated trachea. Br J Pharmacol 1990; 101:541-4. [PMID: 2076475 PMCID: PMC1917732 DOI: 10.1111/j.1476-5381.1990.tb14117.x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
1. The exposure of rat isolated tracheal segment to the K(+)-channel inhibitor tetraethylammonium (TEA, 10 mM) for a period of 10-15 min generally produced little or no contractile response. 2. Cooling (10 C) provocation alone usually produced small (10 +/- 3% acetylcholine maximum) contractile responses. 3. In the presence of TEA (10 mM, 10-15 min exposure), rat trachea exhibited airway hyperreactivity to acetylcholine, 5-hydroxytryptamine (5-HT) and cooling. It also increased the peak tension induced by 5-HT. 4. TEA-induced airway hyperreactivity to cooling was significantly inhibited in Ca2(+)-free Krebs solution suggesting an important role for extracellular Ca2+ influx. 5. We conclude that the blockade of potassium channels with TEA induces non-specific airway hyperreactivity to cooling, 5-HT and acetylcholine in rat isolated tracheal segments.
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Affiliation(s)
- N Chand
- Wallace Laboratories, Division of Carter-Wallace, Inc., Cranbury, New Jersey 08512
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Muraki K, Imaizumi Y, Kojima T, Kawai T, Watanabe M. Effects of tetraethylammonium and 4-aminopyridine on outward currents and excitability in canine tracheal smooth muscle cells. Br J Pharmacol 1990; 100:507-15. [PMID: 1697197 PMCID: PMC1917802 DOI: 10.1111/j.1476-5381.1990.tb15838.x] [Citation(s) in RCA: 56] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
1. The effects of tetraethylammonium (TEA) and 4-aminopyridine (4-AP) on membrane currents and on single channel K currents in smooth muscle cells isolated from canine trachea were examined by use of tight seal whole cell- and patch-clamp techniques. 2. Depolarizing current applied through a recording pipette did not elicit an action potential under current clamp. A strong outward rectification was observed. 3. In most cells under voltage-clamp, only an outward current was observed upon depolarization from -60 mV when a pipette solution contained mainly KCl. The outward current consisted of three components; a large initial transient, a following sustained component and an additional component of irregular small transients on the sustained one. The two transient components were almost abolished when extracellular and pipette solutions contained 2.2 mM Cd2+ (0 mM Ca2+) and 10 mM EGTA, respectively. The sustained component was well maintained under these conditions. 4. TEA at low concentrations (less than 1 mM) effectively decreased the transient components and made the outward current smooth; it also suppressed the sustained component at higher concentrations. In outside-out patches, external 1 mM TEA reduced the single channel conductance of Ca-activated K channels by about 87% whereas 3 mM 4-AP did not. 4-AP at low concentrations (less than 3 mM) selectively reduced the sustained component of the outward current. 5. A Ca current recorded after the suppression of outward current by internal Cs+ had a peak of approximately 200 pA at +10 mV (holding potential: -60 mV). The half inactivation voltage in the steady-state was approximately -30 mV. 6. Simultaneous application of 1 mM TEA and 4-AP reduced the outward current and unmasked a Ca current. Under these conditions, an action potential with overshoot was easily elicited under current clamp. 7. It is concluded that the low excitability of canine tracheal smooth muscle cell upon depolarization is due to a large outward K current which consists of Ca-dependent and Ca-independent components. The peak amplitude of the Ca current is similar to that in highly excitable smooth muscle cells such as those of the ureter.
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Affiliation(s)
- K Muraki
- Department of Chemical Pharmacology, Faculty of Pharmaceutical Sciences, Nagoya City University, Japan
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Richards IS, Kulkarni AP, Brooks SM. Ethanol-induced bronchodilatation in TEA-treated canine tracheal smooth muscle is mediated by a beta-adrenoceptor-dependent mechanism. Eur J Pharmacol 1989; 167:155-60. [PMID: 2550255 DOI: 10.1016/0014-2999(89)90757-7] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
The effects of moderate concentrations of ethanol (8-34 mM) on the electromechanical activity of airway smooth muscle cells of canine trachealis, stimulated by the spasmogen tetraethylammonium (TEA), are described for in vitro and cultured reaggregate preparations. Ethanol produced a concentration-dependent hyperpolarization, and suppression of action potentials in smooth muscle preparations, in vitro, whereas it was without effect in cultured airway smooth muscle cells. In the presence of the beta-adrenoceptor antagonist propranolol (1 microM), ethanol had no effect on in vitro preparations. Isoproterenol (0.1 microM) produced hyperpolarization and suppression of action potentials in airway smooth muscle of both preparations. These effects were not observed when propranolol was additionally present. This suggests that both in vitro, and cultured airway smooth muscle preparations maintained their beta-receptors, and that ethanol caused the release of endogenous catecholamine from adrenergic nerve endings which apparently remained intact in in vitro, but not in cultured airway smooth muscle preparations.
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Affiliation(s)
- I S Richards
- Department of Environmental and Occupational Health, University of South Florida, College of Public Health, Tampa 33612-3899
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18
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Chideckel EW, Anireddy DR, el-Ayoubi N, Singh A. Cyclic nucleotides augment the phasic action of tetraethylammonium on guinea-pig trachealis. Eur J Pharmacol 1989; 166:367-72. [PMID: 2553434 DOI: 10.1016/0014-2999(89)90347-6] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
It is known that after exposure to (3 mM) tetraethylammonium (TEA), guinea-pig isolated trachealis generates tonic spasm followed by phasic tension changes. We found that 8-Br-cAMP or 8-Br-cGMP (10(-6)-5 x 10(-4) M) suppressed tonic spasm secondary to TEA and induced rapid mechanical oscillations. NaN3, forskolin, aminophylline, and isoprenaline had effects similar to those of the cyclic nucleotides. Tetrodotoxin, atropine, diphenhydramine, and cimetidine were without effect on the rapid oscillations. KCl (16 mM) stimulated the oscillations in tissue treated with TEA or TEA plus 8-Br-cGMP. Diltiazem abolished all rhythmic activity in TEA plus 8-Br-cGMP-treated tissues. We conclude: (A) The rapid oscillations are a result of increased cytoplasmic calcium flux with K+ affecting the contractile arm by increasing Ca2+ entry and cyclic nucleotides affecting the relaxant arm by reducing cytosolic free Ca2+. (B) The cyclic nucleotide effect is direct. (C) Cyclic nucleotides may enhance the rate of contraction and relaxation in the presence of some forms of phasic activity.
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Affiliation(s)
- E W Chideckel
- Department of Medicine, West Virginia University, Morgantown 26506
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19
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Smith TK, Reed JB, Sanders KM. Effects of membrane potential on electrical slow waves of canine proximal colon. THE AMERICAN JOURNAL OF PHYSIOLOGY 1988; 255:C828-34. [PMID: 3202152 DOI: 10.1152/ajpcell.1988.255.6.c828] [Citation(s) in RCA: 63] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
The effects of membrane potential on the waveforms and propagation of slow waves were tested using circular muscles of the canine colon. Studies were conducted with intracellular recording techniques on cross-sectional strips of canine proximal colon. Circular muscle cells near the submucosa generated slow waves that decayed in amplitude as they spread through the circular layer. The membrane potentials of cells were less negative as a function of distance from the submucosal border. Cells near the submucosa were depolarized with elevated external K+ and electrical pulses using the partitioned chamber technique. The waveforms of depolarized submucosal cells were compared with events recorded from cells in the bulk of the circular layer. The waveform changes caused by experimental depolarization were different from the changes in waveform that occur during propagation, suggesting the latter are due to a different mechanism than depolarization. The effects of the membrane potential on syncytial input resistance and length constant were also evaluated. The results of these studies are consistent with the hypothesis that slow-wave propagation across the circular layer in canine proximal colon occurs passively.
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Affiliation(s)
- T K Smith
- Department of Physiology, University of Nevada School of Medicine, Reno 89557
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20
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Iwaki M, Nakaya Y, Kawano K, Mizobuchi S, Nakaya S, Mori H. Tetraethylammonium-induced contraction of rabbit coronary artery. Heart Vessels 1988; 4:141-8. [PMID: 2977782 DOI: 10.1007/bf02058426] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
The vasoactive effect of tetraethylammonium (TEA), a well-known K channel blocker, was tested on helical strips excised from the large epicardial coronary arteries of rabbit hearts. TEA (10 mM) induced transient tetanic contraction of greater amplitude as a result of summation of twitch responses. Occasionally, spontaneous periodic contractions occurred during prolonged exposure to 10 mM TEA. This TEA-induced contraction was abolished in Ca-free solution and suppressed by Ca-entry blockers: nitroglycerin, nicorandil, and isoproterenol, but not by phentolamine or atropine. In strips in which TEA did not induce remarkable contraction, subsequent addition of a subthreshold concentration of ergonovine, serotonin, acetylcholine, ouabain, K-rich solution, or alkalinization of the solution provoked remarkable contraction. These results are consistent with previous reports that TEA induced tetanic contraction as a result of summation of twitch responses due to spontaneous discharge of Ca-spikes in some arterial and tracheal smooth muscle. The results also support the idea that TEA-induced contraction of the rabbit coronary artery is mediated by the same mechanism, i.e., spontaneous Ca-spike discharge.
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Affiliation(s)
- M Iwaki
- 2nd Department of Internal Medicine, School of Medicine, University of Tokushima, Japan
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21
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Kotlikoff MI. Calcium currents in isolated canine airway smooth muscle cells. THE AMERICAN JOURNAL OF PHYSIOLOGY 1988; 254:C793-801. [PMID: 2454029 DOI: 10.1152/ajpcell.1988.254.6.c793] [Citation(s) in RCA: 58] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Canine tracheal smooth muscle cells were enzymatically dissociated, and individual myocytes were voltage clamped through use of the whole cell, patch-clamp method. Cells dialyzed with solutions high in potassium and bathed in physiological saline demonstrated brief inward currents, followed by large outward currents that inactivated very slowly. When outward currents were blocked, a voltage-activated inward current was observed that activated with depolarizations to voltages positive to -45 mV, with an apparent reversal potential greater than 110 mV, and a peak current at 15 mV. This current was identified as a calcium current on the basis of 1) its presence under conditions in which calcium was the only permeant cation, 2) the lack of a blocking effect of 2 microM tetrodotoxin, and 3) block of the current by Mn2+, Cd2+, and CO2+. Increases in external calcium concentration from 2 to 20 mM resulted in an increase in current amplitude and a shift of voltage activation toward more positive potentials. The current displayed a rapid inactivation phase with a time constant of 16-52 ms, which was well fit by a single exponential. Steady-state inactivation of the calcium current was sigmoidal, with a voltage of half inactivation of -21 mV in 20 mM Ca2+. The principle component of the calcium current was further identified as a transient current on the basis of its rapid inactivation, current-voltage characteristics, and relative insensitivity to dihydropyridine calcium channel blocking agents.
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Affiliation(s)
- M I Kotlikoff
- Department of Animal Biology, University of Pennsylvania, Philadelphia 19104-6046
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Boyle JP, Davies JM, Foster RW, Good DM, Kennedy I, Small RC. Spasmogen action in guinea-pig isolated trachealis: involvement of membrane K+-channels and the consequences of K+-channel blockade. Br J Pharmacol 1988; 93:319-30. [PMID: 2451965 PMCID: PMC1853808 DOI: 10.1111/j.1476-5381.1988.tb11437.x] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
1. Acetylcholine (ACh), histamine, prostaglandin E2 and potassium chloride (KCl) each evoked concentration-dependent spasm of guinea-pig isolated trachealis treated with indomethacin (2.8 microM). 2. Neither tetraethylammonium (TEA; 0.1-10 mM) nor procaine (0.1-10 mM) potentiated these spasmogens. Indeed, procaine (10 mM) depressed the log concentration-effect curves of all the spasmogens while TEA (1-10 mM) caused some depression of the log concentration-effect curve of prostaglandin E2. 3. Intracellular electrophysiological recording was performed in trachealis bathed by normal Krebs solution or by Krebs solution containing 2.8 microM indomethacin. In either medium the majority of trachealis cells exhibited spontaneous electrical slow waves while some cells were electrically quiescent. In either medium the spasmogenic effects of ACh (1 mM) and histamine (0.2 mM) were accompanied by depolarization and abolition of slow wave discharge. In many cases the record of membrane potential subsequently exhibited noise which incorporated fast, hyperpolarizing transients. 4. In the absence and presence of indomethacin, TEA (10 mM) and procaine (5 mM) markedly reduced the membrane noise and hyperpolarizing transients evoked by ACh or histamine without augmenting the evoked tension. 5. It is concluded that slow wave discharge does not depend on prostaglandin synthesis. The membrane noise and hyperpolarizing transients evoked by ACh and histamine represent the opening of membrane K+-channels. While such K+-channel opening may offset spasmogen-induced depolarization it does not moderate the evoked tension.
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Affiliation(s)
- J P Boyle
- Department of Physiological Sciences, Medical School, University of Manchester
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Mitchell HW. Electromechanical effects of tetraethylammonium and K+ on histamine-induced contraction in pig isolated tracheal smooth muscle. Lung 1987; 165:129-42. [PMID: 3108590 DOI: 10.1007/bf02714429] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
The effect of tetraethylammonium (TEA) and K+ on contractions to histamine and acetylcholine have been compared in the pig isolated trachea using organ bath and sucrose-gap techniques. Histamine elicited weak contractions, compared with acetylcholine; however, these contractions were markedly potentiated by pretreatment with TEA (10 mM) or by raising the external KCl concentration to 30-50 mM. Neither TEA nor K+ increased the sustained depolarization evoked by histamine (or acetylcholine) although oscillatory depolarizations were often observed in the presence of TEA. Verapamil and a zero Ca2+ Krebs solution reduced contractions to histamine and reduced or abolished the effect of TEA and K+ on histamine-induced contractions. The results unmask different mechanisms of contraction for histamine and acetylcholine. Histamine-induced tone appears to be linked with mechanisms sensitive to TEA and high K+, possibly involving increased translocation of Ca2+ across the plasma membrane.
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Giembycz MA, Rodger IW. Electrophysiological and other aspects of excitation-contraction coupling and uncoupling in mammalian airway smooth muscle. Life Sci 1987; 41:111-32. [PMID: 2439865 DOI: 10.1016/0024-3205(87)90485-1] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
In this article the electrophysiological events which are believed to underly agonist-induced contraction and relaxation of airway smooth muscle are reviewed, with special emphasis on the indispensable role of the Ca ion. The contribution made by Na, K, Ca and Cl to, and the role that the electrogenic Na:K-dependent ATPase plays in, the maintenance of the resting membrane potential in both normal and sensitised airway smooth muscle cells is described together with the permeability changes that occur in the plasmalemma in response to excitatory and inhibitory agonists. In addition, the currently available evidence for the existence of potential-sensitive and receptor-operated Ca channels in respiratory smooth muscle, and how such channels may be involved in the regulation of airway calibre, is critically assessed.
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Kirkpatrick CT. A biophysical approach to bronchospasm. Ir J Med Sci 1987; 156:205-10. [PMID: 2443464 DOI: 10.1007/bf02954041] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
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Kamm KE. Myosin light chain phosphorylation during phasic contractions of tracheal smooth muscle. Pflugers Arch 1987; 408:474-8. [PMID: 3601636 DOI: 10.1007/bf00585071] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Rapid, coordinated contractions of tracheal smooth muscle were elicited by either direct electrical depolarization of muscle cells or treatment with tetraethylammonium which produced spontaneous phasic contractile activity. Both types of contraction were blocked by the calcium channel antagonist verapamil, indicating that these contractions are supported primarily by calcium of extracellular origin. With direct electrical stimulation, force was biphasic and phosphate content of the phosphorylatable light chain (P-light chain) of myosin increased rapidly (approximately 2.5 s) from 0.1 to 0.4 mol phosphate/mol P-light chain, then decreased to levels above resting values. Phosphorylation increased more rapidly than force. Under conditions of spontaneous activity, phasic contractions occurred above a level of basal tone significantly greater than resting force, and minimum values of phosphorylation measured at the base of contraction were significantly greater than those observed in the resting muscle. Phosphorylation oscillated with force (from 0.2 to 0.4 mol phosphate/mol P-light chain) and peak values occurred during the rising phase of contraction. Time courses of phosphorylation and force showed evidence of a prolonged state of activation of myosin following dephosphorylation. These results suggest that phosphorylation and dephosphorylation of myosin P-light chain are sufficiently rapid to participate in regulation of contractility during phasic mechanical activity.
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Agrawal R, Daniel EE. Control of gap junction formation in canine trachea by arachidonic acid metabolites. THE AMERICAN JOURNAL OF PHYSIOLOGY 1986; 250:C495-505. [PMID: 3006508 DOI: 10.1152/ajpcell.1986.250.3.c495] [Citation(s) in RCA: 34] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
This study examined whether the synthesis of the metabolites of arachidonic acid (AA) was involved in gap junction formation by 4-aminopyridine (4-AP) treatment in vitro in canine trachealis. Studies were made of the effects on gap junction formation of putative inhibitors of the cyclooxygenase and of both this and the lipoxygenase pathway of AA metabolism and the direct effects of prostaglandins (PG) E2 and I2. The number of gap junctions of similar size was increased after brief exposure to 4-AP. After indomethacin (IDM), 4-AP treatment decreased the number of gap junctions but did not affect their size. Pretreatment with 5,8,11,14-eicosatetraynoic acid or nordihydroguiaretic acid, putative inhibitors of cyclooxygenase and lipoxygenase enzymes, inhibited both the 4-AP-induced increase and decrease in the number of gap junctions. FPL 55712, a putative antagonist of leukotriene C4, did not alter either the number or the size of gap junctions when added alone or in combination with IDM. AA alone increased the number of gap junctions, but after IDM, AA decreased the number of gap junctions compared with the controls. Incubation of trachealis strips in vitro for 30 min with PGE2 increased the number of gap junctions by about threefold along with an increase in the size of the gap junctions. Similar incubation with PGI2, however, increased the number of gap junctions by approximately 60% without any change in the size. In the course of some control experiments, an interaction between carbachol and alcohol was observed such that alcohol caused an IDM-sensitive relaxation of carbachol-induced contractions, which was not observed when serotonin was the contractile agent. These results strongly suggest that PGE2 and PGI2 increase the formation of gap junctions in canine trachealis and that these prostanoids are released by 4-AP treatment. Leukotrienes may also be inhibitory in the formation of gap junctions, but FPL 55712 did not affect either the increase or the decrease in gap junctions after 4-AP.
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Abstract
Airway smooth muscle cells from canine trachealis muscle were dispersed by treatment with collagenase and elastase. Cells were identified as smooth muscle by their binding of anti-smooth muscle gamma-isoactin monoclonal antibodies and by their contraction in response to acetylcholine. The patch-clamp technique was used to study single channel currents in cell-attached and isolated patches of membrane. The most common single channel currents had a conductance of 266 +/- 12 pS (mean +/- S.D., n = 7) in symmetrical 135 mM-K solutions. The reversal potential of the channel was unaltered by large chemical gradients for Cl, Na and Ca and was determined exclusively by the chemical K gradient. Thus, the channel is highly selective for K. In both cell-attached and isolated patches of membrane, depolarization increased the frequency of channel opening and the duration of the open state. In isolated patches of membrane, increasing [Ca] on the cytoplasmic side of the membrane from 10(-8) to 10(-6) M increased both the frequency of channel opening and the duration of the open state. Tetraethylammonium, tetramethylammonium, or Cs (10 mM) on the cytoplasmic side of the membrane caused a voltage-dependent decrease in conductance of the open channel while having no obvious effect on channel kinetics. These blocks were completely reversible. Ba (10 mM) on the cytoplasmic side of the membrane slightly decreased inward currents and completely blocked outward currents through the channel. External Ba (10 mM) caused a voltage-dependent decrease in inward current. External tetraethylammonium (10 mM) completely blocked single channel currents.
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Advenier C, Cerrina J, Duroux P, Floch A, Renier A. Effects of five different organic calcium antagonists on guinea-pig isolated trachea. Br J Pharmacol 1984; 82:727-33. [PMID: 6611187 PMCID: PMC1987015 DOI: 10.1111/j.1476-5381.1984.tb10812.x] [Citation(s) in RCA: 68] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
The relaxant effects of five organic calcium antagonists (nicardipine, diltiazem, PY 108068, verapamil and bepridil) on guinea-pig isolated trachea were tested against contractions induced by acetylcholine, histamine, 5-hydroxytryptamine, potassium chloride (KCl) and tetraethylammonium (TEA) in a medium containing the normal amount of calcium and against calcium dose-response curves in a calcium-free, potassium-enriched medium. These effects were compared with those of spasmolytic or specific acetylcholine or histamine antagonists. In contrast to the other drugs tested, organic calcium antagonists exerted a specific inhibitory effect on KCl- and TEA-induced contractions. Their degree of activity was in the order: nicardipine greater than diltiazem greater than PY 108068 greater than verapamil greater than bepridil. All calcium antagonists inhibited calcium dose-response curves at similar concentrations. Organic calcium antagonists therefore seem to exert a specific inhibitory effect on depolarizing agents in the guinea-pig isolated trachea, unlike other tissues, notably some vascular smooth muscles.
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Foster RW, Small RC, Weston AH. The spasmogenic action of potassium chloride in guinea-pig trachealis. Br J Pharmacol 1983; 80:553-9. [PMID: 6640206 PMCID: PMC2044996 DOI: 10.1111/j.1476-5381.1983.tb10728.x] [Citation(s) in RCA: 56] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
Tissue bath experiments showed that potassium chloride (KC1) at 10-40 mmoll-1 evoked spasm of guinea-pig trachealis which was unaffected by atropine (1 mumoll-1), mepyramine (1 mumoll-1), tetrodotoxin (3 mumoll-1) or indomethacin (2.8 mumoll-1). Spasm evoked by KC1 was depressed in Ca2+-free Krebs solution or by exposure of tissues to LaCl3 (0.25-1 mmoll-1). Extracellular electrical recording showed that the spasm evoked by KCl 10 mmoll-1 was associated with promotion of electrical slow wave activity. Higher concentrations of KC1 abolished slow wave activity but caused further tension development. Intracellular recording confirmed the ability of KC1 10 mmoll-1 transiently to promote slow wave activity in individual trachealis cells. This action was associated with depolarization and tension development. Higher concentrations of KC1 evoked further tension development but slow waves were suppressed as the depolarization evoked by KC1 increased. KC1 (10-40 mmoll-1) increased the lanthanum-resistant calcium fraction of muscle-containing strips of trachea. It is concluded that KC1 acts directly on the smooth muscle of guinea-pig trachea. The spasmogenic action is associated with transient promotion of slow wave activity and a fall in resting membrane potential. The spasm involves the cellular influx of Ca2+ and is dependent on the presence of Ca2+ in the extracellular fluid.
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Dixon JS, Small RC. Evidence of poor conduction of muscle excitation in the longitudinal axis of guinea-pig isolated trachea. Br J Pharmacol 1983; 79:75-83. [PMID: 6871556 PMCID: PMC2044817 DOI: 10.1111/j.1476-5381.1983.tb10498.x] [Citation(s) in RCA: 38] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
1 Mechanical activity was recorded from one segment of guinea-pig trachealis muscle while intracellular electrical activity was simultaneously recorded from a contiguous segment. When the tissue was stimulated by 1-32 mmol/l tetraethylammonium (TEA) it became clear that the electrical and mechanical records were not directly correlated. 2 Dual recording of mechanical activity from two contiguous segments of trachealis revealed that one tissue segment could exhibit phasic activity whilst the other could exhibit tonic activity, despite exposure to the same concentration of TEA. 3 Histological studies revealed that the trachealis muscle was organized into bundles largely separated from one another by spaces filled with connective tissue. However, muscle bundles branched and formed anastomotic connections with near neighbours. 4 It is concluded that the cell to cell spread of muscle excitation is very poor along the longitudinal axis of the trachea. The trachealis muscle as a whole does not function as a single unit. Rather it may represent a series of effector units each comprising a small number of smooth muscle bundles.
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Souhrada M, Klein JJ, Berend N, Souhrada JF. Topographical differences in the physiological response of canine airway smooth muscle. RESPIRATION PHYSIOLOGY 1983; 52:245-58. [PMID: 6878912 DOI: 10.1016/0034-5687(83)90009-9] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
The resting membrane potential (Em), electrical and contractile response were studied in three anatomically separate areas of trachealis muscle and also in bronchial muscle (2nd generation) isolated from mongrel dogs. These responses were studied before and after administration of a single dose of histamine, serotonin, carbachol and prostaglandin F2 alpha. A cross-sectional area of airway smooth muscle in each preparation was directly assessed from the histological sections. These values were used to evaluate isometric tension (in g/mm2). It was found that (1) cross-sectional area of airway smooth muscle varies with location; (2) resting membrane potential of airway smooth muscle from upper, middle and lower portions of dog trachea was similar, i.e., -60.4 +/- 0.8, -60.2 +/- 0.4 and -60.8 +/- 0.9 mV, respectively; (3) resting membrane potential of bronchial airway smooth muscle (2nd generation) was -63.4 +/- 0.5 significantly higher (P less than 0.01) than the membrane potential observed in the trachealis muscle; (4) both contractile and electrical changes after single doses of histamine and serotonin administration showed a vertical gradient response. The largest contractile and electrical responses to these two agents were found in preparations from the lower portion of trachea and the smallest response was observed in upper tracheal preparations; (5) contractile responses after a single dose of carbachol and PGF2 alpha, when expressed as isometric tension also showed vertical gradient. In contrast, membrane potential changes after carbachol and prostaglandin F2 alpha were similar in all three types of tracheal segments. Airway smooth muscle of the 2nd generation of bronchi showed large responses after single doses of histamine, carbachol and prostaglandin F2 alpha but the response after serotonin was smaller than that seen in the lower trachea.
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Foster RW, Small RC, Weston AH. Evidence that the spasmogenic action of tetraethylammonium in guinea-pig trachealis is both direct and dependent on the cellular influx of calcium ion. Br J Pharmacol 1983; 79:255-63. [PMID: 6871547 PMCID: PMC2044808 DOI: 10.1111/j.1476-5381.1983.tb10519.x] [Citation(s) in RCA: 79] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
1 Tetraethylammonium (TEA, 1-8 mmol/l) evoked spasm of guinea-pig trachealis which was unaffected by atropine (1 mumol/l), mepyramine (1 mumol/l) or tetrodotoxin (3 mumol/l). 2 The spasm evoked by TEA was markedly suppressed in Ca2+-free Krebs solution while that evoked by acetylcholine was much less affected. 3 Extracellular electrical recording showed that exposure to Ca2+-free Krebs solution suppressed both spontaneous electrical slow wave activity of the trachea and the spasm and slow waves induced by TEA. These effects were reversible. 4 TEA (2 and 8 mmol/l) increased the lanthanum-resistant calcium fraction of trachea. 5 It is concluded that TEA acts directly on the smooth muscle of guinea-pig trachea, that the spasm and electrical slow waves evoked are Ca2+-dependent and that the cellular influx of Ca2+ is increased.
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Sims SM, Daniel EE, Garfield RE. Improved electrical coupling in uterine smooth muscle is associated with increased numbers of gap junctions at parturition. J Gen Physiol 1982; 80:353-75. [PMID: 7142952 PMCID: PMC2228686 DOI: 10.1085/jgp.80.3.353] [Citation(s) in RCA: 102] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023] Open
Abstract
We have studied some passive electrical properties of uterine smooth muscle to determine whether a change in electrical parameters accompanies gap junction formation at delivery. The length constant of the longitudinal myometrium increased from 2.6 +/- 0.8 mm (X +/- SD) before term to 3.7 +/- 1 mm in tissues from delivering animals. The basis of the change was a 33% decrease in internal resistance and a 46% increase in membrane resistance. Axial current flow in an electrical syncytium such as myometrium is impeded by the cytoplasm of individual cells plus the junctions between cells. Measurement of the longitudinal impedance indicated that the specific resistance of the myoplasmic component was constant at 319 +/- 113 omega . cm before term and 340 +/- 93 omega . cm at delivery. However, a decrease in junctional resistance was apparent from 323 +/- 161 omega . cm to 134 +/- 64 omega . cm at delivery. 1.5-2 d after delivery, the junctional resistance was increased, as was the myoplasmic resistance. Thin-section electron microscopy of some of the same muscle samples showed that gap junctions were present in significantly greater numbers in the delivering tissues. Therefore, our results support the hypothesis that gap junction formation at delivery is associated with improved electrical coupling of uterine smooth muscle.
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37
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Small RC. Electrical slow waves and tone of guinea-pig isolated trachealis muscle: effects of drugs and temperature changes. Br J Pharmacol 1982; 77:45-54. [PMID: 7126995 PMCID: PMC2044649 DOI: 10.1111/j.1476-5381.1982.tb09267.x] [Citation(s) in RCA: 54] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023] Open
Abstract
1 Simultaneous recordings of electrical and mechanical activity have been made from guinea-pig isolated trachealis muscle. Electrical activity was recorded both by extracellular and intracellular techniques.2 Extracellular studies showed that the spontaneous development of tone was accompanied by electrical slow waves which frequently exhibited pronounced waxing and waning. Intracellular recording confirmed the discharge of these slow waves in individual cells. Extracellularly-recorded slow waves were often of greatest amplitude while the tissue was developing rather than maintaining tension. Some tissues became electrically quiescent on reaching peak tone.3 Cooling to 27.5 degrees C caused some relaxation. Slow wave amplitude and frequency fell, slow waves eventually being abolished. Subsequent rapid rewarming initially evoked a more profound relaxation. An intense discharge of slow waves then occurred as the tension rapidly rose again towards the pre-cooling value.4 Sodium nitrite, (-)-isoprenaline, adenosine and adenosine triphosphate (ATP) each evoked relaxation and reduced the frequency and amplitude of slow waves. High concentrations of these agents often abolished slow waves. The actions of these drugs were reversible.5 Treatment with methoxyverapamil (D600) 1 mumol/l for 15 min abolished slow wave activity but only evoked partial relaxation of the tissue.6 Acetylcholine, histamine and tetraethylammonium (TEA) each evoked contraction, but TEA was unique in consistently promoting slow waves and (in high concentration) spike activity. Spasm evoked by acetylcholine and histamine did not usually involve the initiation or promotion of slow waves. Indeed in appropriate concentration these two agents always suppressed slow wave activity. The actions of the spasmogens were reversible.7 It is concluded that the smooth muscle cells of the trachealis are electrically coupled. While co-ordinated slow wave activity is associated with the spontaneous development of tension in trachealis, it may not be necessary for the maintenance of the major part of the spontaneous tension exhibited by the tissue or for the spasm evoked by histamine or acetylcholine. Slow wave promotion by TEA suggests that the tissue may have a high resting potassium conductance which normally attenuates the slow waves. Slow waves may be suppressed by a variety of drugs acting by different mechanisms. Since D600 suppresses slow waves of the trachealis the mechanisms underlying the waves may be similar to those underlying spike activity in other smooth muscles.
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Imaizumi Y, Watanabe M. Effect of procaine on potassium permeability of canine tracheal smooth muscle. Pflugers Arch 1982; 394:144-9. [PMID: 7122220 DOI: 10.1007/bf00582916] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
Procaine depolarized the cell membrane, and initiated oscillations and spike-like potentials in canine tracheal smooth muscle, at concentrations between 1 and 5 mM, while higher concentrations of this drug suppressed the spontaneous activities. Inhibitory effects of procaine on 86Rb-efflux were not evident in normal solution. In high K solution, procaine decreased the rate of 86Rb-efflux, in a dose dependent manner, and a Scatchard plot suggested two sites of action for procaine. The site with a higher affinity (KD = 0.26 mM) may directly regulate the K permeability and interact with procaine in a one to one manner. In high concentrations (greater than or equal to 10 mM), procaine interacted at another site and the tracheal smooth muscle which contracted in high K solution relaxed almost completely. Thus, the decrease in 86Rb-efflux by high concentrations of procaine may partly result from a decrease in intracellular Ca concentration. It is proposed that procaine has the dual effect by inhibiting the K conductance: (1) depolarization of cell membrane, (2) increase in membrane excitability. These actions would explain the spontaneous electrical activity induced by procaine in canine tracheal smooth muscle.
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Souhrada M, Souhrada JF. Reassessment of electrophysiological and contractile characteristics of sensitized airway smooth muscle. RESPIRATION PHYSIOLOGY 1981; 46:17-27. [PMID: 7330489 DOI: 10.1016/0034-5687(81)90065-7] [Citation(s) in RCA: 35] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
Airway smooth muscle preparations were isolated from control guinea pigs, from animals sensitized to albumin and Pertussis vaccine, from sensitized animals which had been resensitized and from animals that had been sensitized and exposed to an inhalation challenge of albumin for 14 days. The resting membrane potential, its changes and contractile response of airway smooth muscle were measured during in vitro antigen challenge, administration of histamine dihydrochloride (10(-3) M), or isoproterenol (10(-3) M). We have found that: (1) The resting membrane potential of normal airway smooth muscle of guinea pig was -61.3 +/- 0.2 mV (+/- SE); (2) Resting membrane potential of airway smooth muscle from sensitized animals was significantly increased (P less than 0.05) to -72.9 +/- 0.3 mV (+/- SE); (3) One week after resensitization of animals a further significant increase (P less than 0.05) in resting membrane potential to -76.2 +/- 0.2 mV (+/- SE) was observed; (4) Resting membrane potential of airway smooth muscle isolated from animals repeatedly exposed to inhalation challenge of antigen significantly decreased (P less than 0.01) to -50.6 +/- 0.5 mV (+/- SE) as compared to controls; (5) After histamine, isoproterenol or antigen administration, the airway smooth muscle from sensitized animals repeatedly exposed to inhalation challenge showed attenuated response (P less than 0.01) as measured by both membrane potential and isometric force. In contrast, the response to antigen and histamine in preparations from sensitized animals is potentiated. It is concluded that both acute sensitization and resensitization on one hand and repeated exposure of sensitized animals to inhaled albumin on the other will alter cellular mechanism(s) responsible for the maintenance of membrane potential and the regulation of excitation-contraction coupling in airway smooth muscle.
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Imaizumi Y, Watanabe M. The effect of tetraethylammonium chloride on potassium permeability in the smooth muscle cell membrane of canine trachea. J Physiol 1981; 316:33-46. [PMID: 7320871 PMCID: PMC1248134 DOI: 10.1113/jphysiol.1981.sp013770] [Citation(s) in RCA: 50] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
Abstract
1. The effect of tetraethylammonium ions (TEA) on potassium or rubidium permeability was studied in canine tracheal smooth muscle. 2. TEA (15-30 mM) markedly increased the rate of 42K- and 86Rb-efflux in normal Krebs solution. This increase is probably due mainly to the occurrence of electrical activity such as spike potentials and only partially to depolarization. 3. The rate coefficients of 42K- and 86Rb-efflux from depolarized tracheal smooth muscle bathed in a medium with elevated potassium (50-100 mM) were so large that the coefficients did not remain constant. When chloride ions in the medium were replaced with larger anions such as acetate, propionate or benzoate, the rate of 86Rb-efflux remained constant even in high-potassium solution (70 mM). 4. TEA caused a remarkable blockade of 86Rb-efflux in depolarized tracheal smooth muscle. The maximum decrease in the rate coefficient by TEA was approximately 52.5% of the control value in high-potassium-acetate solution. The dissociation constant for the interaction between TEA and its sites of action on the cell membrane was about 0.93 mM. 5. Spontaneous activity was, however, elicited only when TEA was added at a concentration of 10-30 mM and the membrane was depolarized more than 15-20 mV. It is assumed that TEA blocks not only the voltage-sensitive potassium conductance but also the conductance in the resting state, and that the latter may be possibly less sensitive to TEA.
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McCaig DJ, Souhrada JF. Alteration of electrophysiological properties of airway smooth muscle from sensitized guinea-pigs. RESPIRATION PHYSIOLOGY 1980; 41:49-60. [PMID: 7394375 DOI: 10.1016/0034-5687(80)90022-5] [Citation(s) in RCA: 35] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
Glass microelectrodes were used to study electrophysiological properties of guinea-pig airway smooth muscle (m. trachealis transversus). The resting membrane potential (Em) of airway smooth muscle was found to be -40.4 +/- 0.5 mV (307 cells, 28 preparations). Twenty-seven percent of all cells successfully impaled showed regular spontaneous electrical activity (amplitude of 2-20 mV, with maximum rate of depolarization 15.0 +/- 2.2 mV . sec-1). Forty-four percent of cells showed irregular fluctuations in Em and the remaining cells showed no electrical activity. All three groups of cells had a similar distribution of individual Em values. The sensitization of animals (14 days incubation period) caused a slight but significant increase (P less than 0.001) in Em to -43.1 +/- 0.9 mV. Repeated daily exposure of sensitized animals to aerosolized albumin for two weeks caused a significant reduction of Em to -27.8 +/- 0.8 mV (P less than 0.001). Five weeks repeated exposure caused a further reduction in Em of airway smooth muscle cells to -22.6 +/- 0.7 mV (P less than 0.001). The responses to both histamine (10(-4) M) and isoprenaline (5 x 10(-6) M), as gauged by changes in Em, were altered in the trachea of chronically exposed guinea-pigs. The changes in airway smooth muscle electrical properties were related to the number of times the animals were exposed to inhaled antigen. Even after two weeks of daily exposure, the changes were marked. Airway smooth muscle alteration may be important in the pathogenesis of bronchial asthma.
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Haeusler G, Thorens S. Effects of tetraethylammonium chloride on contractile, membrane and cable properties of rabbit artery muscle. J Physiol 1980; 303:203-24. [PMID: 7431231 PMCID: PMC1282887 DOI: 10.1113/jphysiol.1980.sp013281] [Citation(s) in RCA: 44] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
1. Two types of effects of tetraethylammonium chloride (TEA) have been found in the smooth muscle cells of the rabbit main pulmonary artery. (a) With rapid onset of action TEA depolarizes the cell membrane, increases the membrane resistance, causes anomalous rectification and occasionally spike potentials in response to externally applied depolarizing current pulses and produces tonic contractions. (b) During prolonged (greater than 30 min) incubation in TEA phasic contractions develop progressively and the vascular strips respond to electrical stimulation with synchronized and powerful contractions. 2. There is a linear relationship between log concentration TEA and depolarization over the range of 10-100 mM-TEA. TEA (10 and 30 mM) raises the membrane resistance and decreases the core resistance. The latter effect appeared to develop more slowly than the former. 3. During short exposure to TEA part of the smooth muscle cells respond to depolarizing current pulses with spike potentials of variable amplitude and duration. These spikes are very sensitive to inhibition by verapamil or nickel chloride but are not affected by tetrodotoxin. The amplitude of electrotonic potentials, increased by TEA, is slightly further elevated by verapamil or nickle chloride. 4. TEA (10 mM) increases the mechanical response to low and intermediate potassium concentrations but has no effect on maximal contractions to high potassium. The slope of the line relating log potassium concentration to membrane potential is decreased by TEA. 5. TEA (10 mM) shifts the concentration response curve for the contractile effect of noradrenaline to the left and increases the maximum of noradrenaline-induced contractions. In the presence of TEA, noradrenaline reduces the membrane potential to markedly lower values than under control conditions. 6. It is concluded that the rapidly occurring effects of TEA on the vascular smooth muscle cells of the rabbit main pulmonary artery are a decrease in potassium and an increase in calcium conductance. The latter effect may be related to a blockade of potassium channels; however, we cannot rule out the possibility that TEA affects calcium conductance independent of its presumed action on potassium channels. The slowly developing effects of TEA may be ascribed to the formation of gap junctions and/or (less likely) to an intracellular accumulation of TEA.
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Kannan MS, Daniel EE. Structural and functional study of control of canine tracheal smooth muscle. THE AMERICAN JOURNAL OF PHYSIOLOGY 1980; 238:C27-33. [PMID: 7356008 DOI: 10.1152/ajpcell.1980.238.1.c27] [Citation(s) in RCA: 26] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
The structural bases for myogenic and neurogenic control of canine tracheal smooth muscle were studied. At optimum lengths, strips of muscle showed insignificant neurogenic or myogenic tone. Atropine and/or tetrodotoxin blocked the contractile responses elicited on electrical field stimulation of intrinsic nerves. After raising the tone with tetraethylammonium ion and in the presence of atropine, field stimulation of nerves caused a relaxation, a major component of which was blocked by propranolol and/or tetrodotoxin, suggesting an effect mediated through interaction of mediator released from sympathetic nerves with beta-adrenergic receptors. Electron microscopic studies revealed gap junctions between extensions of smooth-muscle cells and a sparse innervation. The axonal varicosities, corresponding to cholinergic (predominantly) and adrenergic (occasionally) nerves, were seen predominantly in the clefts between cell bundles. The physiological responses were compared with the morphological features. Although this muscle exhibits multiunit behavior in vitro, implying that nerves initiate the coordinate activity, its ultrastructural features suggest a potential for single-unit behavior.
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Ozaki H, Urakawa N. Na-Ca exchange and tension development in guinea-pig aorta. NAUNYN-SCHMIEDEBERG'S ARCHIVES OF PHARMACOLOGY 1979; 309:171-8. [PMID: 522902 DOI: 10.1007/bf00501226] [Citation(s) in RCA: 41] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
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Kannan MS, Daniel EE. Formation of gap junctions by treatment in vitro with potassium conductance blockers. J Cell Biol 1978; 78:338-48. [PMID: 690170 PMCID: PMC2110136 DOI: 10.1083/jcb.78.2.338] [Citation(s) in RCA: 64] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
Gap junctions were regularly seen in thin sections of canine tracheal smooth muscle incubated in vitro. Their number was increased in tissued exposed in vitro to either of two potassium conductance blockers, tetraethylammonium (TEA) and 4-aminopyridine (4-AP), and at the same time the muscles became mechanically active, with spontaneous contractions. The presence of gap junctions in this smooth muscle may provide one basis for cell-to-cell coupling, and their increase after TEA- and 4-AP-treatment could account for a decreased junctional resistance between cells, contributing to a longer space constant. However, an increase in gap junctions was not sufficient to change the behavior of trachealis smooth muscle from multiunit to single-unit type. Gap junctions in increased numbers persisted after washout of 4-AP, which caused inhibition of spontaneous contractions, and despite inhibition of the contractile effects of 4-AP by atropine. The rapid induction of gap junction formation was not dependent on de novo synthesis of protein. The fact that the number of gap junctions can be increased by chemical agents has important implications for control of their formation and provides a tool for analysis fo their role in cell-to-cell coupling.
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Szurszewski JH. A study of the canine gastric action potential in the presence of tetraethylammonium chloride. J Physiol 1978; 277:91-102. [PMID: 650594 PMCID: PMC1282379 DOI: 10.1113/jphysiol.1978.sp012262] [Citation(s) in RCA: 30] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
1. The effects of tetraethylammonium (TEA) ion on the action potential of isolated longitudinal muscle of the dog antrum were used to gain some insight into the mechanism of generation of the plateau potential of the action potential complex. The double sucrose gap was used. 2. In concentrations of TEA up to 5 mM, the amplitude of the upstroke potential was increased. In 10mM-TEA there was also an increase in the amplitude of the plateau potential and in the maximum rate of rise of the upstroke potential. 3. Concentrations of TEA (3 mM and greater) increased the duration of the action potential. Five mM-TEA produced spike potentials which occurred only during the plateau potential of the action potential. Each spike caused a contraction. 4. The steady-state voltage-current relation was studied in normal Krebs solution and in TEA containing Krebs solution. In normal Krebs solution the voltage response was not a linear function of the applied current when outward current pulses were used. In TEA solution the voltage response was a linear function of the entire range of applied depolarizing current. 5. In low concentrations of TEA (2-4 mM), when the steady-state voltage-current relation was linear, constant current pulses were applied between action potentials and during the plateau potential to determine if there were a decrease in membrane slope resistance during the plateau. It was found that the amplitude of the electrotonic potential recorded during the plateau was significantly less than the amplitude of the electrotonic potential recorded between action potentials. 6. The rate of repolarization of the plateau potential was studied in normal Krebs solution and in 2 mM-TEA Krebs solution. The rate of repolarization of the plateau potential was slowed in TEA Krebs solution. 7. It is concluded that there is an increase in the membrane conductance during the plateau potential. The repolarization following the plateau potential is due to a TEA-sensitive outward current.
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Bose R, Bose D. Excitation-contraction coupling in multiunit tracheal smooth muscle during metabolic depletion: induction of rhythmicity. THE AMERICAN JOURNAL OF PHYSIOLOGY 1977; 233:C8-13. [PMID: 406798 DOI: 10.1152/ajpcell.1977.233.1.c8] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Multiunit canine tracheal smooth muscle responded to carbachol with graded depolarization and tonic contraction. The same concentration of carbachol, after metabolic depletion by substrate removal, produced rhythmic contractions and action potentials. Similar mechanical effects were also observed with acetylcholine or histamine. These effects were reversed by reintroducing glucose or beta-hydroxybutyrate, but not by 3-O-methylglucose, which is not metabolized; hence, the structural requirements for glucose, per se, or any osmotic effect were ruled out. Sensitivity to extracellular Ca2+ was increased. A Ca2+-influx blocker, D-600, in low concentration (2 X 10(-8) M) abolished the rhythmic contractions without affecting the tonic contraction. Progressive metabolic depletion in presence of carbachol led to fluctuations in membrane potential with a crest of depolarization and appearance of action potentials, each of which resulted in a small contraction. Many of the small contractions partially fused to form the major rhythmic contractions which appeared at a frequency of one per minute. Rhythmicity could not be produced by increasing extracellular K+ concentration (20-120 mM) in presence of atropine (13(-7) M), but instead a tonic contraction occurred. These results suggest changes in excitation-contraction coupling mechanism with agonists like acetylcholine, carbachol, or histamine during substrate deprivation.
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