1
|
Dalla Fontana M, Anesi S, Czopowicz M, Corr SA. Assessment of potential maladaptive pain in dogs with elbow osteoarthritis using a von Frey aesthesiometer. Vet Rec 2024:e4043. [PMID: 38575548 DOI: 10.1002/vetr.4043] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2023] [Revised: 12/11/2023] [Accepted: 02/15/2024] [Indexed: 04/06/2024]
Abstract
BACKGROUND This study aimed to investigate the possible presence of maladaptive pain in the thoracic limbs of dogs with elbow osteoarthritis (OA) using an electronic von Frey aesthesiometer (eVFA). METHODS Twenty-eight client- and staff-owned dogs (OA, n = 14; controls, n = 14) were enrolled in the study. Every dog underwent a full orthopaedic examination, and then five von Frey measurements were obtained from each carpal pad of each dog. A maximum test threshold of 400 g was set and approved by an ethics committee. RESULTS eVFA thresholds were significantly lower (p < 0.001) in dogs with OA (median 248 g, range 128-369 g) than in control dogs (median 390 g, range 371-400 g). In the OA group, the sensory threshold was significantly lower (p = 0.048) in the more severely affected limb than the less severely affected limb. LIMITATION The low maximum threshold required for ethical approval may influence the variability in the control group. CONCLUSIONS Dogs with elbow OA had significantly lower sensory thresholds than control dogs, which is compatible with the presence of maladaptive pain, potentially due to central sensitisation. Further research is required to evaluate the potential use of the eVFA for monitoring clinical progression and treatment response in dogs with elbow OA.
Collapse
Affiliation(s)
- Maria Dalla Fontana
- Small Animal Hospital, School of Biodiversity, One Health & Veterinary Medicine, University of Glasgow, Scotland, UK
- Blaise Veterinary Referral, Birmingham, UK
| | - Simone Anesi
- Small Animal Hospital, School of Biodiversity, One Health & Veterinary Medicine, University of Glasgow, Scotland, UK
- Willows Veterinary Centre and Referral Service, Solihull, UK
| | - Michal Czopowicz
- Division of Veterinary Epidemiology and Economics, Institute of Veterinary Medicine, Warsaw University of Life Sciences-SGGW, Warsaw, Poland
| | - Sandra A Corr
- Small Animal Hospital, School of Biodiversity, One Health & Veterinary Medicine, University of Glasgow, Scotland, UK
| |
Collapse
|
2
|
Marshall WG, Filliquist B, Tzimtzimis E, Fracka A, Miquel J, Garcia J, Fontana MD. Delayed union, non-union and mal-union in 442 dogs. Vet Surg 2022; 51:1087-1095. [PMID: 36053918 PMCID: PMC9804201 DOI: 10.1111/vsu.13880] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2022] [Revised: 06/23/2022] [Accepted: 08/08/2022] [Indexed: 01/05/2023]
Abstract
OBJECTIVES (1) To estimate the prevalence of delayed union, non-union and mal-union in canine fractures; (2) to describe fracture, demographic, and treatment characteristics for these outcomes; (3) to identify risk factors for delayed or non-union. STUDY DESIGN Retrospective study. SAMPLE POPULATION Four hundred and forty two dogs (461 fractures). METHODS A review was conducted of clinical records and radiographs from 2 teaching hospitals. "Union," "delayed union," "non-union" and "mal-union" were defined, and fracture, demographic, treatment, and outcome variables described. Differences in proportions or medians between "union," "delayed union" and "non-union" were tested using χ2 and Mann-Whitney U-tests for categorical and continuous variables respectively. Potential explanatory variables for "delayed or non-union" were tested using logistic regression to identify risk factors. RESULTS Median radiographic follow up was 53 days (14-282). Delayed union occurred in 13.9% of fractures (64/461), non-union in 4.6% (21/461), and mal-union in 0.7% (3/461). Risk factors for delayed or non-union were age (OR 1.21, 95% CI 1.12-1.31); comminuted fracture (OR 4.24, 95% CI 2.4-7.5); treatment with bone graft (all types) (OR 3.32, 95% CI 1.3-8.5); surgical site infection (OR 3.24, 95% CI 1.17-8.97), and major implant failure (OR 12.94, 95% CI 5.06-33.1). CONCLUSION Older dogs, dogs with comminuted fractures, surgical site infection, or major implant failure were at increased odds of delayed or non-union. Radius and ulna fractures in toy breed dogs were not at increased odds of delayed or non-union. CLINICAL SIGNIFICANCE The identified risk factors should inform fracture planning and prognosticating. The prognosis for radial fractures in toy breeds appears better than historically believed.
Collapse
Affiliation(s)
| | - Barbro Filliquist
- Department of Surgical and Radiological Sciences, School of Veterinary MedicineUniversity of California DavisDavisCaliforniaUSA
| | - Emmanouil Tzimtzimis
- Small Animal Hospital, School of Veterinary MedicineUniversity of GlasgowGlasgowUK
| | - Agnieszka Fracka
- Small Animal Hospital, School of Veterinary MedicineUniversity of GlasgowGlasgowUK
| | - Jose Miquel
- Small Animal Hospital, School of Veterinary MedicineUniversity of GlasgowGlasgowUK
| | - Javier Garcia
- Small Animal Hospital, School of Veterinary MedicineUniversity of GlasgowGlasgowUK
| | - Maria Dalla Fontana
- Small Animal Hospital, School of Veterinary MedicineUniversity of GlasgowGlasgowUK
| |
Collapse
|
3
|
Durlach R, Kaufer F, Carral L, Freuler C, Ceriotto M, Rodriguez M, Freilij H, Altcheh J, Vazquez L, Corazza R, Dalla Fontana M, Arienti H, Sturba E, Gonzalez Ayala S, Cecchini E, Salomon C, Nadal M, Gutierrez N, Guarnera E. [Argentine Consensus of Congenital Toxoplasmosis]. Medicina (B Aires) 2008; 68:75-87. [PMID: 18416325] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/26/2023] Open
Abstract
The mother-to-child transmission in Toxoplasma gondii infection occurs only when the infection is acquired for the first time during pregnancy. The prenatal and early postnatal diagnosis can only be achieved by serological testing. Serologic tests have different sensitivities, specificities and complexities, so that different tests in more than one blood sample are necessary for the diagnosis. Serological follow-up of the infants should be conducted during the first year of life or until the diagnosis of congenital toxoplasmosis can be ruled out. Treatment recommendations try to reduce the transmission rate and the risk of congenital damage. Congenital toxoplasmosis incidence rate is approximately 5 per 1000 births, but can be reduced to 0.5 per 1000 with an active screening program. The aim of this consensus group was to review the scientific literature on congenital toxoplasmosis and prepare a statement on prevention, diagnosis and treatment that should be implemented in our country.
Collapse
|
4
|
Fontana MD, Metrat G, Servoin JL, Gervais F. Infrared spectroscopy in KNbO3through the successive ferroelectric phase transitions. ACTA ACUST UNITED AC 2000. [DOI: 10.1088/0022-3719/17/3/020] [Citation(s) in RCA: 217] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
|
5
|
|
6
|
Kugel GE, Fontana MD, Hafid M, Roleder K, Kania A, Pawelczyk M. A Raman study of silver tantalate (AgTaO3) and its structural phase transition sequence. ACTA ACUST UNITED AC 2000. [DOI: 10.1088/0022-3719/20/9/012] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
|
7
|
Kugel GE, Brehat F, Wyncke B, Fontana MD, Marnier G, Carabatos-Nedelec C, Mangin J. The vibrational spectrum of a KTiOPO4single crystal studied by Raman and infrared reflectivity spectroscopy. ACTA ACUST UNITED AC 2000. [DOI: 10.1088/0022-3719/21/32/011] [Citation(s) in RCA: 130] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
|
8
|
|
9
|
Brazil OV, Fontana MD, Heluany NF. Nature of the postsynaptic action of crotoxin at guinea-pig diaphragm end-plates. J Nat Toxins 2000; 9:33-42. [PMID: 10701179] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 02/15/2023]
Abstract
Crotoxin is known to desensitize the nicotinic receptor of Torpedo marmorata and Electrophorus electricus electroplaques. The aim of the present study was to elucidate whether the postsynaptic effect of crotoxin at a mammalian muscle end-plate is also caused by receptor desensitization or results from a curaremimetic action. For this purpose, we investigated the action of 4-aminopyridine (4-AP) on crotoxin-induced blockade of miniature end-plate potentials (m.e.p.p.s) and of the depolarization of end-plates produced by carbachol. The experiments were carried out in guinea-pig diaphragms bathed in Tyrode solution at 37 degrees C and gassed with 95% O2, 5% CO2. The potentials were measured with conventional techniques using glass microelectrodes. Even at low concentrations, crotoxin blocked the m.e.p.p.s and this blockade was antagonized by 4-AP. Neostigmine was without effect. 4-AP did not restore the m.e.p.p.s blocked by either d-tubocurarine (dTc) or beta-bungarotoxin (beta-BTX). 4-AP also antagonized the crotoxin-induced blockade of the end-plate depolarization produced by carbachol. These results show that the postsynaptic effect of crotoxin at the guinea-pig muscle end-plate also results from nicotinic receptor desensitization.
Collapse
Affiliation(s)
- O V Brazil
- Department of Pharmacology, Faculty of Medical Sciences, State University of Campinas (UNICAMP), SP, Brazil
| | | | | |
Collapse
|
10
|
Abstract
The effects of Ancylometes sp. venom on muscle contraction and bioelectrical potentials were investigated in the rat phrenic nerve diaphragm muscle preparation. The venom (50 microg/ml) depolarized the diaphragm muscle fiber membranes. This effect was abolished by tetrodotoxin and by reduction of the sodium concentration of the Tyrode solution. The increase in the frequency of miniature end plate potentials induced by the venom was also suppressed by tetrodotoxin (3 microM). These results indicate that the venom may activate voltage-dependent sodium channels in cell membranes. All of the effects of Ancylometes sp. venom on this nerve muscle preparation (i.e. increase in twitch tension, spontaneous small phasic contractions and increase in the frequency of miniature end-plate potentials) may be explained in terms of its action on sodium channels.
Collapse
Affiliation(s)
- A M Grégio
- Department of Pharmacology, Faculty of Odontology (UNICAMP), Piracicaba, SP, Brazil
| | | | | | | |
Collapse
|
11
|
Mattiello-Sverzut AC, Fontana MD, Diniz CR, da Cruz-Höfling MA. Pathological changes induced by PhTx1 from Phoneutria nigriventer spider venom in mouse skeletal muscle in vitro. Toxicon 1998; 36:1349-61. [PMID: 9723834 DOI: 10.1016/s0041-0101(98)00012-9] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The 'armed' spider Phoneutria nigriventer is responsible for most human accidents involving spiders in Brazil. The effects of fraction Tx1 (PhTx1) from the venom of this spider were investigated by physiological and morphological methods using the mouse phrenic nerve-diaphragm preparation. PhTx1 (1 and 5 microg) did not affect the twitch tension of muscle fibers under indirect electrical stimulation. At this same concentration, PhTx1 also did not alter the miniature end-plate potential (mepp) frequency and amplitude, nor did it change the resting membrane potential 60 min after addition to the preparation. Light microscopy (LM) revealed that in muscles incubated with PhTx1 a number of fibers were morphologically altered, as evidenced by microvacuolization and myofibril hypercontraction and loss within 15 min after toxin administration. Transmission electron microscopy (TEM) showed sarcoplasmic reticulum swelling, disorganization of the sarcomeres and mitochondrial damage, and occasionally, sarcolemmal discontinuities with a persisting basal membrane. The intra-muscular fascicles of the phrenic nerve showed myelinated axons with vacuolated myelin sheaths as well as peri- and intra-axoplasmic vacuoles. The neuromuscular junction changes were variable, but were rarely severe. Thus, although PhTx1 did not depolarize or hyperpolarize the neuromuscular junction, it was nevertheless toxic to a restricted number of muscle fibers and nerve structures. The site of action of PhTx1 may involve the sarcolemma and axolemma as suggested by the morphological abnormalities which could reflect hydroelectrolytic disturbances.
Collapse
|
12
|
Fontana MD, Heleno MG, Brazil OV. Mode of action of Duvernoy's gland extracts from the colubrid Dryadophis bifossatus in the chick biventer cervicis nerve-muscle preparation. Toxicon 1996; 34:1187-90. [PMID: 8931259 DOI: 10.1016/0041-0101(96)00066-9] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Extracts and secretion of the Duvernoy's gland are venomous, inducing in several cases motor paralysis in experimental animals. The extracts of the Duvernoy's gland from the aglyphous colubrid Dryadophis bifossatus are very toxic, eliciting flaccid paralysis in pigeons, rabbits and Hylae (Brazil and Vellard, 1926). In the present study, the neuromuscular action of the extracts of Duvernoy's gland from this Colubridae was investigated in the chick biventer cervicis nerve-muscle preparation. The muscle was indirectly stimulated with supramaximal pulses, and by addition of acetylcholine or carbachol to the organ bath. Direct muscle stimulation was carried out in curarized preparations. The extracts induced an irreversible neuromuscular blockade and also inhibited irreversibly the contracture of the biventer cervicis produced by either acetylcholine or carbachol. The twitches elicited by direct muscle stimulation were not depressed. These results show that the neurotoxin(s) of the extracts interact with the end-plate cholinergic receptors.
Collapse
Affiliation(s)
- M D Fontana
- Department of Pharmacology, Faculty of Medical Sciences, State University of Campinas(UNICAMP), Brazil
| | | | | |
Collapse
|
13
|
Abstract
The number of tetrodotoxin molecules bound to the membrane of the fibres of muscles in normal conditions and after detubulation produced by glycerol-induced osmotic shock pointed to a higher sodium channel density at the surface membrane than at the membrane in the transverse tubules. Study of the maximum rate of rise of the action potential at the junctional and nonjunctional regions of the muscle fibre membrane suggested that the Na+ channel density is also not the same along the muscle fibre membrane, being higher at the junctional region. Further studies on the distribution of the Na+ channel along the muscle fibre membrane were carried out with the use of (1) the loose patch voltage-clamp technique, (2) labelling the Na+ channels with fluorescently labelled scorpion toxins, (3) autoradiography of localized Na+ channels with 125I-labelled scorpion toxins, and (4) toxins that induce persistent activation of the Na+ channel. The studies referred to in (1), (2) and (3) demonstrate that the density of the Na+ channel is much higher at the junctional region than elsewhere in the membrane of the muscle fibre. On the other hand, in experiments carried out on curarized rat diaphragms several sodium channel activating toxins (crotamine, Phoneutria nigriventer venom, its toxin PhTx2, veratrine) were found to produce a much greater depolarization of the membrane at the junctional region than at nonjunctional regions. However, it was also found that some toxins (veratridine, batrachotoxin) depolarized equally well the junctional and nonjunctional regions. Two alternative hypotheses to explain the uniform depolarization of the muscle fibre membrane induced by these toxins are suggested.
Collapse
Affiliation(s)
- O V Brazil
- Department of Pharmacology, Faculty of Medical Sciences, State University of Campinas, São Paulo, Brazil
| | | |
Collapse
|
14
|
Etchepare J, Grillon G, Antonetti A, Loulergue JC, Fontana MD, Kugel GE. Third-order nonlinear susceptibilities and polariton modes in PbTiO3 obtained by temporal measurements. Phys Rev B Condens Matter 1990; 41:12362-12365. [PMID: 9993709 DOI: 10.1103/physrevb.41.12362] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
|
15
|
Fontana MD, Kugel GE, Carabatos-Nedelec C. Comment on "Direct observation of relaxation modes in KNbO3 and BaTiO3 using inelastic light scattering". Phys Rev B Condens Matter 1989; 40:786-787. [PMID: 9990984 DOI: 10.1103/physrevb.40.786] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
|
16
|
Brazil OV, Fontana MD, Pavani NJ. Effect of 4-aminopyridine on the postsynaptic action of polymyxin B. Eur J Pharmacol 1989; 159:47-51. [PMID: 2540012 DOI: 10.1016/0014-2999(89)90042-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Polymyxin B produces neuromuscular blockade by acting at pre- and postsynaptic sites. Its postsynaptic effect has been attributed either to blockade of open ionic channels or to the conversion of the end-plate receptor from a low to a high affinity state, i.e. to a state similar to the desensitized one caused by agonists. Since 4-aminopyridine inhibits agonist-induced end-plate receptor desensitization, we decided to investigate its effect on the postsynaptic action of polymyxin B. The experiments were carried out on the isolated rat diaphragm; miniature end-plate potentials (m.e.p.p.s) and carbachol-induced depolarization at the end-plate region were recorded with microelectrode techniques. Polymyxin B, 40 micrograms/ml reduced the amplitude of the m.e.p.p.s and suppressed them in about 30 min. 4-Aminopyridine completely antagonized this effect. Neostigmine did not restore the m.e.p.p.s suppressed by polymyxin B nor did 4-aminopyridine antagonize the effect of d-tubocurarine on these potentials. The carbachol-induced depolarization was blocked only partially by polymyxin B. 4-Aminopyridine B nearly completely antagonized this effect. The antagonistic effect of 4-aminopyridine on the postsynaptic action of polymyxin B favors the receptor desensitization' hypothesis.
Collapse
Affiliation(s)
- O V Brazil
- Department of Pharmacology, Faculty of Medical Sciences, State University of Campinas, São Paulo, Brazil
| | | | | |
Collapse
|
17
|
Oliveira MJ, Fontana MD, Giglio JR, Sampaio SV, Corrado AP, Prado WA. Effects of the venom of the Brazilian scorpion Tityus serrulatus and two of its fractions on the isolated diaphragm of the rat. Gen Pharmacol 1989; 20:205-10. [PMID: 2714618 DOI: 10.1016/0306-3623(89)90016-5] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
1. The effects of Tityus serrulatus venom and of two of its toxic fractions, toxin gamma (Tx gamma) and T2III1, on the rat isolated diaphragm were examined. 2. The crude venom (5 ng) facilitated the neuromuscular transmission and increased the twitch tension evoked by retrograde injection of Ach. 3. Tx gamma (25-100 ng) and fraction T2III1 (2.5 ng) also facilitated the neuromuscular transmission but only fraction T2III1 increased the twitch tension evoked by retrograde injection of Ach. 4. Tx gamma (50 ng) and fraction T2III1 (2.5 ng) produced a tetrodotoxin-sensitive increase in the frequency of miniature endplate potentials (m.e.p.p.) and a transitory reduction of the resting potential. The latter effect of the fractions was prevented by treating muscles with tetrodotoxin or D-tubocurarine. Fraction T2III1 also produced a tetrodotoxin-resistance increase of m.e.p.p. amplitude. 5. These results suggest that Tx gamma enhances Ach output through the activation of Na+ channels in the motor nerve terminals. Fraction T2III1 produced effects similar to those induced by Tx gamma but also acted at postjunctional sites, probably by increasing subsynaptic membrane sensitivity to the neurotransmitter.
Collapse
Affiliation(s)
- M J Oliveira
- Department of Pharmacology, Faculty of Medicine of Ribeirão Preto, Brazil
| | | | | | | | | | | |
Collapse
|
18
|
Kugel GE, Mesli H, Fontana MD, Rytz D. Experimental and theoretical study of the Raman spectrum in KTa1-xNbxO3 solid solutions. Phys Rev B Condens Matter 1988; 37:5619-5628. [PMID: 9943756 DOI: 10.1103/physrevb.37.5619] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/11/2023]
|
19
|
|
20
|
Vogt H, Fontana MD, Kugel GE, Günter P. Low-frequency dielectric response in cubic KNbO3 studied by hyper-Raman scattering. Phys Rev B Condens Matter 1986; 34:410-415. [PMID: 9939276 DOI: 10.1103/physrevb.34.410] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/11/2023]
|
21
|
Abstract
The effect produced by veratrine on transmembrane potential was investigated in five distinct regions of the isolated rat diaphragm blocked with either d-tubocurarine or alpha-bungarotoxin. It was found that small (0.4 micrograms/ml) and large (2.0 micrograms/ml) doses of veratrine depolarize only two or three of these regions. With the use of a very large (10.0 micrograms/ml) dose depolarization occurred in all five regions of the diaphragm but the effect was much larger in those areas of the muscle fibre membrane which were selectively depolarized by the smaller ones. These results clearly indicate either an unequal distribution of sodium channels activated by veratrine or differences in sodium channel density in distinct areas of the muscle fibre membrane. Supersensitivity of veratrinized muscles to potassium was confirmed. However, the sensitiveness to the depolarizing action of potassium was only increased in the regions of the diaphragm partially depolarized by veratrine. This suggests that partial depolarization of the muscle fibre membrane was actually the cause of the supersensitivity. The possible involvement of potassium and of the unequal depolarization of the muscle fibre membrane in the veratrine response is considered.
Collapse
|
22
|
Abstract
The effect of 4-aminopyridine on receptor desensitization was investigated in the isolated rat diaphragm by measuring transmembrane potential in the end-plate region. When 4-aminopyridine was added to the bath before carbachol, the depolarization produced by the agonist was permanent, that is 4-aminopyridine completely inhibited the receptor desensitization produced by prolonged exposure of the receptors to carbachol. When it was added after carbachol in the phase in which the membrane had already repolarized, the end-plate region depolarized. Therefore, 4-aminopyridine was also able to reverse the receptors from the desensitized state to the resting non-desensitized one. The effect of 4-aminopyridine was concentration-dependent. Calcium antagonized the effect of 4-aminopyridine. 4-Aminopyridine also reversed the receptors from their desensitized state to the resting one in the isolated and chronically denervated rat hemidiaphragm. The known action of the aminopyridines cannot explain the effect of 4-aminopyridine described here. It is suggested that it is caused by an action on either the receptor-ionic channel complex or the lipids of the postjunctional membrane surrounding it.
Collapse
|