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  • 1
    ISSN: 0022-2828
    Keywords: Cat papillary muscle ; Contraction-excitation recoupling ; Excitation-contraction coupling ; Length dependent activation ; Quick release ; Quick stretch ; Sucrose gap technique ; Tension transients
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Medicine
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-2013
    Keywords: Cardiac muscle ; Electro-mechanic coupling ; Mechano-electric recoupling ; Contractile deactivation ; Active state
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract 1. A quick release of an isometrically contracting cat papillary muscle results in a depression of the ability to redevelop tension (deactivation) and an increase in the duration of the accompanying action potential (prolonged depolarization). The nature of the mechanical perturbation influencing both phenomena was investigated. 2. The prolongation of the action potential depends on the amplitude of the release and the time it is applied and, provided quick release-quick restretch cycles of less than 50 ms are used, on the duration of the cycle. 3. No change in action potential duration is observed, if initial muscle length, or the velocity of shortening is altered, or if the muscle is stretched at any time during contraction. 4. Although stretches and releases both have a “deactivating” effect on the muscle the effect is more pronounced with releases. This difference in “deactivation” is related to the prolongation of the action potential in so far as it is also controlled by the time and extent of release and release-restretch cycle duration, and is independent of shortening velocity. 5. Caffeine (8 mmol/l) in the bathing solution prolongs isometric tension development whilst the duration of the action potential is relatively unchanged. Under these conditions release-restretch cycles applied at times when the membrane has apparently repolarized, produce a deactivation and an after depolarization which can reach threshold to elicite an action potential. 6. If the membrane is partially depolarized by increasing extracellular potassium to 20 mmol/l, release-restretch cycles still induce deactivation but no change in the action potential. 7. The results are in keeping with the hypothesis that shortening during contraction partly contributes to the deactivating effect by reducing the concentration of internal free ionic calcium. This change in [Ca]i decreases the outward potassium current to produce a prolongation of depolarization which can take the form of an increase in action potential duration or an afterdepolarization wave.
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  • 3
    ISSN: 1432-2013
    Keywords: Contraction-Excitation Recoupling ; Cardiac Force Velocity Relation ; Quick Release ; Controlled Release ; Active State ; Intracellular Action Potentials ; Mechano-elektrische Rückkoppelung ; Kraft-Geschwindigkeitsrelation ; “quick release” ; kontrollierter Release ; “active state” ; intracelluläre Aktionspotentiale
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Zusammenfassung An isolierten Katzenpapillarmuskeln wurden intracelluläre Potentialmessungen bei verschiedenen Kontraktions-Bedingungen durchgeführt. Es wurde gefunden, daß die Aktionspotentialdauer (in Grenzen von etwa 20%) von der Kontraktionsform abhängig ist. Während isotonischer Verkürzung wird das Aktionspotential verlängert, bei isometrischer Spannungsentwicklung abgekürzt. Als Folge dieser Aktionspotential-Veränderungen entwickeln sich treppenartige Zu-oder Abnahmen der mechanischen Aktivität während der folgenden 5–10 Kontraktionen. Durch Anwendung einer kontrollierten Dehnung konnte die Verkürzungsgeschwindigkeit des contractilen Elements (V CE ) kleiner als bei isometrischen Bedingungen gemacht werden. Dabei wurde eine weitere Aktionspotentialverkürzung beobachtet. WurdeV CE dagegen durch Entlastungsexperimente (quick release) über die bei leicht belasteten isotonischen Kontraktionen entwickelte Verkürzungsgeschwindigkeit hinaus erhöht, so ergab sich eine weitere Zunahme der Aktionspotentialdauer. Release-Experimente, die nach der vollständigen Repolarisation durchgeführt wurden, führten zur Auslösung einer neuen Repolarisationswelle von 10–15 mV Amplitude. Zuweilen wurde hierdurch ein neues Aktionspotential ausgelöst. Die Entlastungsexperimente ermöglichten die Abschätzung der “mechanoelektrischen Latenzzeit” des beschriebenen Rückkoppelungssystems. Diese betrug weniger als 10 msec. Die beschriebenen Phänomene lassen sich vermutlich nicht auf Änderungen der membranären Oberflächengeometrie zurückführen. Andere Erklärungsmöglichkeiten werden als Arbeitshypothesen diskutiert. Es erscheint zumindest sicher, daß der Control-Parameter des beschriebenen Rückkoppelungssystems in der Kraft-Geschwindigkeits-Relation des contractilen Elementes selbst zu suchen ist. Möglicherweise bestimmt dessen Kontraktionsform die Dynamik der kontraktionswirksamen Calciumbewegungen.
    Notes: Summary Measurements of transmembrane potentials were performed under different contractile conditions on isolated cat papillary muscles. It was found that the duration of the action potential (within limits of about 20%) depends on the mode of contraction. Isotonic shortening tends to prolong, isometric tension development tends to shorten the duration of the action potential. As a result of the action potential alterations negative or positive inotropic mechanical transients are observed during 5–10 subsequent beats. The decrease in action potential duration is roughly proportional to the force development, and the increase of action potential duration is related to the shortening velocity. By applying a controlled stretch the shortening velocity of the contractile element (V CE ) was reduced below its value during purely isometric conditions. A further decrease of the action potential duration was observed. IncreasingV CE by release experiments increased the action potential duration beyond that observed under lightly loaded isotonic contractions. A quick release taking place after repolarization is complete produces a new distinct wave of depolarization (10–15 mV) which can sometimes initiate a new action potential. The quick release experiments fascilitated the estimation of the time delay of the feedback interaction which is less than 10 msecs. The possibility that passive geometrical changes of the plasma membrane is a causitive factor of the described phenomenon was experimentally excluded. Alternative explanations are discussed. It seems likely that a controlling parameter of this excitation contraction feedback system is contained in the force velocity relation of the contractile element influencing the internal Ca++-transients by its mode of contraction.
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  • 4
    ISSN: 1573-2622
    Keywords: Glare ; Haze ; Keratectomy ; Myopia ; Photorefractive ; Straylight
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract We performed a study to evaluate the influence on visual function of intraocular straylight after photorefractive keratectomy (PRK). We present 4 eyes of 4 myopic individuals, who had contacted our clinic for keratorefractive surgical treatment. PRK's were performed with a Summit laser, using a 5 mm ablation zone. The straylight meter was used to measure the amount of intraocular scattered light, the physical cause of glare complaints, before and after PRK. This apparatus uses the direct compensation method to assess the amount of intraocular light scatter. The results showed a significant increase in straylight values, in the tested eyes, during the first two weeks after PRK. After the initial rise, straylight values returned to preoperative levels, except for two eyes that clearly developed a haze higher than grade two. Instead of returning to baseline levels, straylight values remained significantly higher in these eyes.
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  • 5
    ISSN: 1432-1912
    Keywords: Verapamil ; D 600 ; Cardiac Muscle ; Amplitude-Frequency Relation ; Staircase Phenomena
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary A pattern analysis of inotropic actions was carried out on isotonically shortening cat papillary muscles exposed to (±)-verapamil and (±)-D 600 and compared to other Ca-antagonistic interventions. 1. (±)-Verapamil (1–5 μg/ml) leaves contraction amplitudes nearly unchanged at 6/min, whereas at 60/min more than 90% depression (5 μ/ml) occurs. (±)-D 600 is about twice as effective as (±)-verapamil. 2. An increase of [Ca2+]0 in the presence of (±)-verapamil or (±)-D 600 does not restitute the normal amplitude-frequency relationship. There is only a shift toward higher contraction amplitudes. 3. (±)-Verapamil and (±)-D 600 lead to typical biphasic inotropic transients after step changes of the driving rhythm. First a fast and (at higher frequencies) very pronounced negative staircase occurs, followed by a rather slowly developing positive staircase. 4. These drug effects contrast to the effects of lowering [Ca2+]0 or of adding Ni2+ or La3+, which all produce a rather uniform depression of contraction amplitudes at all frequencies and do not elicit staircase phenomena such as seen under the influence of (±)-verapamil or (±)-D 600. 5. In contrast to the action of Ni2+, La3+ or low [Ca2+]0, (±)-verapamil slows down the restitution kinetics of Ca-reavailability from internal stores as determined by the amplitude of test contractions elicited after various periods of rest. 6. Drug-induced changes in the time course of the transmembrane action potential as depending on frequency may partially but not fully explain the contractile phenomena. 7. Possible interpretations as to the sites where (±)-verapamil or (±)-D 600 interferes with cardiac excitation-contraction coupling are given by the aid of a multicompartment model. This model describes excitation-contraction coupling in terms of transmembrane and intracellular Ca-movements.
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  • 6
    ISSN: 1432-1912
    Keywords: Nifedipine ; Mammalian cardiac muscle ; Amplitude-frequency relationship ; Staircase phenomena ; Transmembrane action potential ; SA-nodal rate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary 1. The effects of nifedipine (3×10−11–3×10−6 M) on contractile activity and transmembrane action potential (AP) were studied in isotonically contracting cat papillary muscles and in isolated SA-nodes. 2. Nifedipine (3×10−8–3×10−6 M) reduces the amplitudes of contraction. The effect is nearly independent of stimulation rate such that at 6/min the ED50 amounts to 6.1×10−7 M as compared to 5.1×10−7 M at 60/min. This negative inotropic action can be nearly completely antagonized by raising [Ca2+] o . 3. Nifedipine induces short-lasting negative stair-cases developing upon step increases of stimulation rate. Raising [Ca2+] o does not counteract this effect. 4. Nifedipine exerts a dual action on the amplitudeinterval relationship for simple test contractions elicited after a variable period of rest and preceding conditioning stimulation: (i) a flattening of the initial part of the “restitution” curve and (ii) a depression of the steady-state level reached after 2–10 s of rest. Raising [Ca2+] o elevates the steady state to control level but does not reestablish the initial slope of the curve. 5. Nifedipine, while leaving resting potential, maximum rate of depolarization and overshoot unaffected, tends to abbreviate the AP duration. Since this effect is more pronounced at lower frequencies, the usual prolongation of the AP occurring at low stimulation rates is inhibited. The AP plateau is depressed, but this effect seems to be stronger at higher stimulation rates. 6. In isolated SA nodes nifedipine (3×10−7–1×10−6 M) decreases discharge rate by reducing both the rate of the slow diastolic depolarization and the maximal diastolic potential until intranodal conduction blocks occur. 7. It is concluded that the negative inotropic action of nifedipine results mainly from diminished transmembrane Ca supply, with a slight action on internal sites of cardiac e.-c. coupling.
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  • 7
    ISSN: 1432-1912
    Keywords: Isolated human iris ; Carbachol ; Atropine ; Muscarine receptor
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Concentration-dependent contractions in response to carbachol were determined on isolated pieces of human iris. Atropine competitively antagonized the effect of carbachol. An apparent dissociation equilibrium constant of 0.4–0.7 nM was estimated for the muscarine receptor-atropine complex.
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  • 8
    ISSN: 1435-702X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Zusammenfassung Bei 66 nicht vorselektierten Kindern mit Schädel-Hirn-Traumen (SHT) unterschiedlicher Schweregrade wurden die visuell evozierten Potentiale (VECP) nach Blitzreizen abgeleitet. Bewertet wurden lediglich Differenzen im corticalen Potential zwischen beiden Hemisphären und/oder zwischen beiden Augen. Dabei ergab sich in 23 Fällen ein pathologisches VECP. Eine Einteilung des SHT Schweregrades nach Lange-Cosack und Tepfer (I–VI) führt zu einer engen Korrelation zwischen der Häufigkeit pathologischer VECP und dem Schweregrad des Traumas. Bei leichten Verletzungen (I–II) waren die VECP-Veränderungen nur vorübergehend, bei schweren Traumen (III–VI) waren sie dauerhaft. VECP- und EEG-Befunde stimmten in 2/3 der Fälle bezüglich der Aussage „pathologisch“ oder „nicht pathologisch“ überein. In 1/3 der Fälle ergaben sich Nichtübereinstimmungen insoweit, als beide Methoden zu unterschiedlichen Bewertungen kamen.
    Notes: Abstract Sixty-six randomly selected children with concussive head injuries of different degrees were subjected to visual evoked potential to flash examination (VECP). Evaluating only the differences in occipital potential between both hemispheres and/or both eyes, the VECP was pathological in 23 cases. Estimating the severity of the head injuries, according to the proposal of Lange-Cosack and Tepfer (grades I–VI), gave rise to a close correlation between the incidence of pathological VECP and increasing degree of trauma. VECP changes were usually transitory in nature with slight injuries (I and II) and constant in traumata of higher degrees (III–VI). As to the agreement of VECP and EEG findings, in two-thirds of the cases, the results of both methods coincided with respect to the indication of “pathological” or “nonpathological”. In one-third the methods gave different results.
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  • 9
    ISSN: 1435-702X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Zusammenfassung Das Elektroretinogramm (ERG) des Menschen, ausgelöst durch kurze (10 μs) Lichtblitze zeigt eine typische Abhängigkeit von der Blitzintensität. Mit steigender Reizintensität strebt die Amplitude der a-Welle einem Sättigungswert zu, wohingegen die Amplitude der b-Welle ein Maximum durchläuft um dann bei höchsten Reizintensitäten wieder abzufallen. Der Sättigungswert der a-Wellenamplituden, als 100% definiert, ermöglicht eine Normierung der Amplituden-Intensitätsfunktionen für die a- und b-Wellen. Die normierte b-Wellenfunktion zeigt nach Dunkel- und Helladaptation einen unterschiedlichen Maximalwert, der — im Gegensatz zu den absoluten Spannungswerten — geringeren interindividuellen Schwankungen unterliegt. Bei einer Ethambutolintoxikation ist die Differenz zwischen normierter maximaler b-Wellenamplitude nach Helladaptation und nach Dunkeladaptation signifikant vermindert. ERG Veränderungen offenbaren sich aber nur in Fällen schwerer Ethambutol-intoxikation (absolutes Zentralskotom) und unterschreiten die Nachweisbarkeitsgrenze in leichteren Fällen (relatives Zentralskotom, Visus 0,4–0,5).
    Notes: Abstract The human electroretinogram (ERG), evoked by white flashes of extremely short duration (10 μs), shows a typical dependence on flash intensity. Increasing stimulus intensity increases the amplitude of the a-wave until saturation is reached. The amplitude of the b-wave reaches a maximum value with flashes of middle intensity, then decreases at higher stimulus strengths. The values of a-wave amplitude saturation, defined as 100%, may serve as a basis for standardizing the various amplitude-intensity relationships of the a- and b-wave. The b-wave function, calculated in this way, shows different maximum values depending on whether it was determined after light adaptation or in dark adaptation and low interindividual variability. However, the difference between bmax in dark and light adaptation is markedly decreased in the case of ethambutol intoxication. ERG changes are only detected in severe cases (total central scotoma) and are below the discrimination level in cases with moderate symptoms (relative central scotoma, visual acuity 〉 0.4–0.5).
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  • 10
    ISSN: 1435-702X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The saccadic eye movements of young diabetic subjects (type I) were analyzed with respect to their synchronism (30° gaze jumps). Regarding the duration (end) of saccadic eye movements, it was found that in diabetics (n = 41) the asymmetry between both eyes (≦ 35 ms) is appreciably more than in normal individuals of equivalent age (n = 25; ≦ 10 ms). The asynchronism described is closely correlated with the hemoglobin AIc concentration in the blood.
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