Influence of osmolarity of perfusate on contractility of mammalian myocardium

1963 ◽  
Vol 204 (6) ◽  
pp. 957-962 ◽  
Author(s):  
Jan Koch-Weser
Keyword(s):  
Time Course ◽  
Muscle Tension ◽  
Water Concentration ◽  
Myocardial Contraction ◽  
Papillary Muscles ◽  
Tension Development ◽  
Mammalian Myocardium ◽  
Spontaneous Contractions ◽  
External Stimuli ◽  
Osmolar Concentration

The effect of changes in the osmolarity of the perfusing fluid on strength and time course of myocardial contraction was studied in cat papillary muscles and atrial strips. Osmolar concentration was varied by adding up to 750 mm sucrose or mannitol to a slightly hypoosmolar solution, leaving molar concentrations of the original solutes unchanged. Optimum osmolarity for tension development by papillary muscles was close to that of serum (330 mosmol/ liter), but for atrial muscles was 150 mosmol/liter higher. Osmolarity changes apparently influence contractility by altering the intracellular water concentration. Increases of osmolarity up to the optimum augment tension development by increasing the degree of activation of the contractile elements. This may be due to increased concentration of calcium in a superficial area of the fiber. Increases of osmolar concentration above the optimum lower developed tension, probably by reducing the intrinsic speed of the muscle. Tension development in response to external stimuli is abolished by raising osmolarity to three times that of serum (1 osmol/liter). Spontaneous contractions cease in solutions of twice normal osmolar concentration.

Epithelial vs. serosal stimulation of tracheal muscle: role of epithelium

1989 ◽  
Vol 67 (6) ◽  
pp. 2522-2526 ◽  
Author(s):  
D. Pavlovic ◽  
M. Fournier ◽  
M. Aubier ◽  
R. Pariente
Keyword(s):  
Time Course ◽  
Muscle Tension ◽  
Active Role ◽  
Force Transducer ◽  
Tension Development ◽  
In Vitro System ◽  
Pharmacological Stimulation ◽  
Stimulation Of

There is evidence implying an active role of airway epithelium in the modulation of bronchomotor tone. To study this phenomenon, we designed an in vitro system allowing pharmacological stimulation of either the inside or outside of the airway lumen. Rat tracheas were excised, cannulated, and their inside and outside perfused independently with Krebs solution. Two hooks were inserted through opposite sides of the tracheal wall, the lower one was attached to a fixed point, while the upper one was connected to a force transducer. Isometric contractions of the tracheal muscle were elicited by carbachol solution perfused in single and cumulative concentrations. In one-half of the preparations the epithelium was mechanically removed. Stimulation of the inside or outside of the trachea produced equal maximal tracheal muscle tension [1.55 +/- 0.14 and 1.2 +/- 0.09 (SE) g in and out, respectively]. The time course of tension development was longer when carbachol was administered inside the trachea: an effect that was abolished when the epithelium was removed. In addition, removal of the epithelium was found 1) to increase the maximal tension irrespective of the route of carbachol perfusion and 2) to increase the sensitivity of the preparation to carbachol stimulation.

Na+–K+ transport, motility and tegumental membrane potential in adult male Schistosoma mansoni

Parasitology ◽  
1981 ◽  
Vol 82 (1) ◽  
pp. 97-109 ◽  
Author(s):  
R. H. Fetterer ◽  
R. A. Pax ◽  
J. L. Bennett
Keyword(s):  
Membrane Potential ◽  
Schistosoma Mansoni ◽  
Adult Male ◽  
Time Course ◽  
Muscle Tension ◽  
Transport Systems ◽  
Effect Of Temperature ◽  
Bathing Medium ◽  
Tension Development ◽  
Tension Increase

SUMMARYOuabain applied to adult male Schistosoma mansoni causes a large, non-reversible tension increase of the parasite's musculature and elimination of spontaneous contractions. The tension increase and the time-course of tension development caused by ouabain are dose dependent with significant effects obtained at 3 × 10−6m. Digoxin and digoxigenin act in a similar manner with a relative potency of ouabain ≃ digoxin > digoxigenin. Lowered temperature as well as substitution of Li+ for Na+ increases muscle tension. The membrane potential recorded from the ventral tegument is also affected by treatments which interact with Na+–K+ transport systems. Ouabain (0·1 mm) causes a rapid depolarization without a significant effect on membrane resistance. The tegument is depolarized by temperatures below 30 °C. The effect of temperature is readily reversible and the temperature sensitivity is eliminated by pretreatment with ouabain. Substitution of Li+ for Na+ also causes a depolarization of the tegument. Tracer experiments show both an increase in Na+ and a decrease in K+ in the parasite within 10 min after treatment with ouabain (1 × 10−5m). Decreasing temperature of the bathing medium also causes an accumulation of Na+ as well as a decrease in the animals. The above results indicate a significant role for active Na+–K+ transport in muscle contraction and in maintenance of the tegumental membrane potential. The data also suggest that the Na+–K+ transport in S. mansoni may be electrogenic.

Respiratory and cardiovascular responses to static handgrip exercise in humans

1993 ◽  
Vol 75 (6) ◽  
pp. 2789-2796 ◽  
Author(s):  
G. A. Fontana ◽  
T. Pantaleo ◽  
F. Bongianni ◽  
F. Cresci ◽  
R. Manconi ◽  
...  
Keyword(s):  
Heart Rate ◽  
Time Course ◽  
Minute Ventilation ◽  
Muscle Tension ◽  
Maximum Voluntary Contraction ◽  
Cardiovascular Responses ◽  
Inspiratory Flow ◽  
Electromyographic Activity ◽  
Handgrip Exercise ◽  
Cardiovascular Variables

We studied the time course of respiratory and cardiovascular responses by evaluating changes in the breathing pattern, mean blood pressure (MBP), and heart rate elicited by 3 min of static handgrip at 15, 25, and 30% of the maximum voluntary contraction (MVC) in 15 healthy volunteers. Muscle tension and integrated electromyographic activity remained fairly constant during each trial. During 15% MVC bouts, initially only mean inspiratory flow increased; then, tidal volume and minute ventilation (VI) also rose progressively. No significant changes in MBP and heart rate were observed. During 25 and 30% MVC bouts, not only did mean inspiratory flow, VT, and VI increase but MBP and heart rate increased as well. A slight and delayed rise in respiratory rate was also observed. Unlike 15 and 25% MVC handgrip, 30% MVC handgrip caused a small decrease in end-tidal PCO2. Changes in the pattern of breathing occurred more promptly than those in cardiovascular variables in the majority of subjects. Furthermore, we found a positive correlation between changes in VI and those in cardiovascular variables at the end of 25 and 30% MVC trials. This study indicates that respiratory and cardiovascular responses to static handgrip exercise are controlled independently.

Gradation of isometric tension by different activation rates in motor units of cat flexor carpi radialis muscle

1986 ◽  
Vol 56 (2) ◽  
pp. 494-506 ◽  
Author(s):  
B. R. Botterman ◽  
G. A. Iwamoto ◽  
W. J. Gonyea
Keyword(s):  
Muscle Tension ◽  
Motor Units ◽  
Isometric Tension ◽  
Medial Gastrocnemius ◽  
Potential Contribution ◽  
Tension Development ◽  
Stimulus Interval ◽  
Flexor Carpi Radialis ◽  
Single Motor Units ◽  
Activation Rates

Single motor units of the flexor carpi radialis (FCR) muscle were activated with a series of constant-rate stimulus trains to study the relation between the frequency of activation and isometric tension development (F-T relation). The tension produced by each stimulus train was expressed as a percentage of the maximum tension-time area (Amax) found for a given unit. Between 25 and 75% Amax a clear separation was seen in the rates needed to produce the same relative tension for the F-T curves of slow-twitch (type S) and fast-twitch (type F) units. Over the steepest portion of the F-T curve (25-50% Amax), where tension output was most sensitive to changes in activation rate, type F units required substantially higher stimulation rates (30 pps) to achieve the same relative tension output as type S units. Furthermore, the frequency range that corresponded to the steep portion of the curve was 2.3 times greater for type F units. For both type S and F units, twitch duration was deemed to be an important determinant of the F-T curve, as has been shown previously. A direct continuous relation was seen between the integrated twitch time (ITT) and the stimulus interval needed to produce 50% Amax (r = 0.94, P less than 0.001). Thus, units that had relatively brief twitches required higher activation rates to achieve the same relative percentage of Amax. Comparison of F-T curves from FCR with those derived by other investigators for cat hindlimb units (medial gastrocnemius and peroneus longus) revealed that significant differences in activation rates were needed to produce the same percentage of Amax throughout the midrange of the F-T curve. At 50% Amax, type F units in FCR required activation rates approximately 20 pps higher than type F units in the hindlimb. Type S units in FCR required only slightly higher rates (approximately equal to 5 pps). Based on a number of well-founded assumptions, F-T curves derived from FCR units were used to estimate the potential contribution of rate coding to total muscle tension by type S and F units. This analysis leads to the conclusion that rate modulation is a potentially important factor in the gradation of tension for the FCR muscle.

Potentiation of Neuromuscular Transmission by an Octopaminergic Neurone in the Locust

1979 ◽  
Vol 79 (1) ◽  
pp. 169-190 ◽  
Author(s):  
MICHAEL O'SHEA ◽  
PETER D. EVANS
Keyword(s):  
Indirect Effects ◽  
Neuromuscular Transmission ◽  
Time Course ◽  
Muscle Tone ◽  
Muscle Tension ◽  
Presynaptic Receptors ◽  
Extensor Muscle ◽  
Muscle Membrane ◽  
Muscle Fibres ◽  
Central Synapses

1. Spikes in the octopaminergic dorsal unpaired median (DUM) neurone which innervates the extensor tibiae muscle of the locust metathoracic leg (DUMETi) produce direct and indirect effects on muscle tension. 2. Direct effects include a slowing of an intrinsic rhythm of contraction and relaxation, a relaxation of muscle tone and a small hyperpolarization of the muscle membrane potential. The latter two effects are weak and variable. All three effects are mimicked by superfusion of octopamine and are mediated by octopamine receptors on the muscle fibres. 3. Indirect effects are found when the DUMETi neurone is stimulated at the same time as the motoneurones innervating the extensor muscle. They include (a) potentiation of tension generated in the extensor muscle by spikes in the slow excitatory motoneurone (SETi), (b) reduction in duration of each twitch contraction generated by SETi due to an increase in the rate at which the muscle relaxes, (c) increase in the amplitude of the synaptic potential generated by SETi. These various effects have a time course of several minutes and far outlast the duration of DUMETi stimulation. They can be mimicked by superfusion of octopamine. 4. The effect of DUMETi on neuromuscular transmission is mediated by receptors with a high affinity for octopamine located both on the muscle and on the terminals of the slow motoneurone. The presence of the presynaptic receptors is revealed by the increase in the frequency of spontaneous miniature end plate potentials recorded in the muscle in the presence of octopamine. 5. DUMETi is a member of a group of similar aminergic neurones and it is suggested that they may share a role in modulating transmission at peripheral neuromuscular synapses, and possibly central synapses.

Time course of postnatal changes in rat heart action potential and in transient outward current is different

1994 ◽  
Vol 267 (3) ◽  
pp. H1157-H1166 ◽  
Author(s):  
G. M. Wahler ◽  
S. J. Dollinger ◽  
J. M. Smith ◽  
K. L. Flemal
Keyword(s):  
Action Potential ◽  
Rat Heart ◽  
Action Potentials ◽  
Time Course ◽  
Outward Current ◽  
Transient Outward Current ◽  
Papillary Muscles ◽  
Isolated Cells ◽  
Time Courses ◽  
Action Potential Shortening

The rat ventricular action potential shortens after birth. The contribution of increases in the transient outward current (Ito) to postnatal action potential shortening was assessed by measuring Ito in isolated cells and by determining the effect of 2 mM 4-aminopyridine (4-AP) on the action potentials of papillary muscles. 4-AP had no effect on 1-day action potential duration at 25% repolarization (APD25), and 1-day cells had little Ito. In 8- to 10-day muscles, 4-AP caused a small, but significant, increase in APD25. Ito increased slightly between day 1 and days 8-10, but this increase was not significant. Most of the increase in Ito (79%) and in the response to 4-AP (64%) occurred between days 8-10 and adult; however, approximately 75% of the APD25 shortening took place by days 8-10. Thus, while Ito may contribute to repolarization in late neonatal and adult cells, the different time courses of action potential shortening and increases in Ito suggest that changes in Ito are unlikely to be responsible for most of the postnatal action potential shortening.

Pharmacological evidence for two types of myocardial sarcoplasmic reticulum Ca2+ release

1991 ◽  
Vol 260 (3) ◽  
pp. H785-H795
Author(s):  
C. Lynch
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Local Anesthetics ◽  
Papillary Muscles ◽  
Initial Tension ◽  
Tension Development ◽  
Short Cycle ◽  
Peak Tension ◽  
Low Concentrations ◽  
Cycle Lengths ◽  
Initial Delay

Contractions of guinea pig papillary muscles were studied at 37 degrees C under a variety of conditions and stimulation rates that markedly alter the pattern of tension development. When rested-state contractions (RSCs) were enhanced by treatments that increase intracellular adenosine 3',5'-cyclic monophosphate (0.1-1 microM isoproterenol, 1-10 microM forskolin), a markedly enhanced late peak tension developed after a 100-ms delay. Such late peak tension was selectively depressed by local anesthetics (200-400 microM procaine, 4-10 microM tetracaine, or 0.5-1 mM ethyl aminobenzoate). In contrast, 0.1-1 microM ryanodine had little effect on late peak tension, whereas 5 mM caffeine reduced the delay before tension development. Inotropic interventions such as increased external Ca2+ concentration or the Ca2+ channel agonist BAY K 8644 did not elicit such distinct late peaking RSCs. Rapid initial tension development observed under a variety of situations (short cycle lengths, stimulation rates of 0.25 Hz plus isoproterenol, decreased external Na+ concentration) was markedly depressed by 0.01-1 microM ryanodine and by caffeine, whereas local anesthetics had little effect. These results suggest two pharmacologically distinct types of sarcoplasmic reticulum Ca2+ release: 1) Ca2+ that accumulates during prior depolarizations is released immediately upon depolarization and decreased by ryanodine and caffeine; 2) extracellular Ca2+ that enters the myocyte is accumulated and released after an initial delay and is selectively depressed by low concentrations of local anesthetics.

Effect of cocaine and methylecgonidine on intracellular Ca2+ and myocardial contraction in cardiac myocytes

1997 ◽  
Vol 273 (2) ◽  
pp. H893-H901 ◽  
Author(s):  
L. Huang ◽  
J. H. Woolf ◽  
Y. Ishiguro ◽  
J. P. Morgan
Keyword(s):  
Structural Damage ◽  
Time Course ◽  
Crack Cocaine ◽  
Pyrolysis Product ◽  
Myocardial Contraction ◽  
Dependent Manner ◽  
Response Curves ◽  
Inotropic Effects ◽  
Cell Shortening ◽  
Dose Dependent

We evaluated the cardiac effects of the principle pyrolysis product of crack cocaine smoking, methylecgonidine (MEG), in comparison with cocaine. Peak cell shortening and intracellular Ca2+, as detected by the Ca2+ indicator indo 1, were recorded in enzymatically isolated ferret myocytes. Both cocaine and MEG decreased peak cell shortening and peak intracellular Ca2+ concentration ([Ca2+]i) in a dose-dependent manner (10(-8)-10(-4) M). MEG shifted the peak [Ca2+]i-to-peak shortening relationship downward and was more potent than cocaine. Atropine (10(-6) M) upwardly shifted the dose-response curves of MEG, cocaine, and carbachol but not of procaine. The negative inotropic effects of MEG were inhibited by methoctramine, a selective M2 receptor blocker but not by M1 (pirenzepine) or M3 (4-diphenylacetoxy-N-methylpiperidine methiodide) blocking agents. In contrast to cocaine, the effects of large doses of MEG were irreversible over the time course of our experiments, raising the possibility of structural damage. We conclude that MEG acts primarily on M2 cholinergic receptors in the heart to produce acute cardiac intoxication and, in contrast to cocaine, may decrease the myofilament Ca2+ responseness and cause structural damage to myocytes by a direct toxic effect.

Effect of rate changes on strength and time course of contraction of papillary muscle

1963 ◽  
Vol 204 (3) ◽  
pp. 451-457 ◽  
Author(s):  
Jan Koch-Weser
Keyword(s):  
Entire Range ◽  
Maximum Rate ◽  
Time Course ◽  
Normal Development ◽  
Papillary Muscles ◽  
Ventricular Muscle ◽  
High Frequencies ◽  
Peak Tension ◽  
Time To Peak ◽  
Opposing Effect

The influence of 14 frequencies of contraction (between 0.2 and 300 beats/min) on the development of tension and on the time course of contraction was determined in 40 isometrically contracting, isolated cat papillary muscles at 38 C. Only cylindrical muscles with radius <0.43 mm were included, since this was found to be the maximum thickness compatible with normal development of tension at high frequencies. Increases in frequency were associated over the entire range with decreases in the time to peak tension (total 40%) and in the relaxation time (total 49%), and increases in the maximum rate of development of tension (total 560%) and in the peak tension developed (total 340%). These findings indicate that changes in heart rate alter both the degree of activation of the contractile elements and the duration of their active state. It is concluded that the opposing effect of both of these changes must be considered in any analysis of the influence of alterations in rate or rhythm of the heart on the strength of contraction of mammalian ventricular muscle.

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