Refractoriness in Cardiac Muscle

1957 ◽  
Vol 190 (3) ◽  
pp. 473-482 ◽  
Author(s):  
Brian F. Hoffman ◽  
C. Y. Kao ◽  
E. E. Suckling
Keyword(s):  
Action Potential ◽  
Cardiac Muscle ◽  
Refractory Period ◽  
Action Potentials ◽  
Transmembrane Potential ◽  
Local Response ◽  
Applied Current ◽  
Two Factors ◽  
Cardiac Fiber ◽  
Stimulation Of

A preparation consisting of a papillary muscle and attached bundle of Purkinje fibers has been employed to study refractoriness of single cardiac fibers of the dog heart. Transmembrane stimulation of single fibers and records of the transmembrane potential have been used to compare the stimulating efficacy of applied current pulses and normally propagated action potentials. The absolute and effective refractory period and full recovery time of the single cardiac fiber are outlined in a similar manner by both applied cathodal stimuli and the propagated action potential. Two factors, a local response and a change in the local action potential, have been shown to contribute to the latency of response to stimuli applied during the relative refractory period. These studies have also demonstrated a considerable safety factor in propagation in cardiac muscle.

scholarly journals CHARACTERIZATION OF SIGNAL CONDUCTION ALONG DEMYELINATED AXONS BY ACTION-POTENTIAL-ENCODED SECOND HARMONIC GENERATION

2014 ◽  
Vol 07 (01) ◽  
pp. 1330003 ◽  
Author(s):  
ZHI-HUI LUO ◽  
JIANG-XU CHEN ◽  
YI-MEI HUANG ◽  
HONG-QIN YANG ◽  
JU-QIANG LIN ◽  
...  
Keyword(s):  
Action Potential ◽  
Second Harmonic Generation ◽  
Harmonic Generation ◽  
Refractory Period ◽  
Action Potentials ◽  
Demyelinating Disease ◽  
Second Harmonic ◽  
Temporal Distribution ◽  
Demyelinating Diseases

Action-potential-encoded optical second harmonic generation (SHG) has been recently proposed for use in detecting the axonal damage in patients with demyelinating diseases. In this study, the characterization of signal conduction along axons of two different levels of demyelination was studied via a modified Hodgkin–Huxley model, because some types of demyelinating disease, i.e., primary progressive and secondary progressive multiple sclerosis, are difficult to be distinguished by magnetic resonance imaging (MRI), we focused on the differences in signal conduction between two different demyelinated axons, such as the first-level demyelination and the second-level demyelination. The spatio-temporal distribution of action potentials along demyelinated axons and conduction properties including the refractory period and frequency encoding in these two patterns were investigated. The results showed that demyelination could induce the decrease both in the amplitude of action potentials and the ability of frequency coding. Furthermore, the signal conduction velocity in the second-level demyelination was about 21% slower than that in the first-level demyelination. The refractory period in the second-level demyelination was about 32% longer than the first-level. Thus, detecting the signal conduction in demyelinated axons by action-potential-encoded optical SHG could greatly improve the assessment of demyelinating disorders to classify the patients. This technique also offers a potential fast and noninvasive optical approach for monitoring membrane potential.

Effect of Several Cations on Transmembrane Potentials of Cardiac Muscle

1956 ◽  
Vol 186 (2) ◽  
pp. 317-324 ◽  
Author(s):  
Brian F. Hoffman ◽  
E. E. Suckling
Keyword(s):  
Action Potential ◽  
Cardiac Muscle ◽  
Action Potentials ◽  
Time Course ◽  
Pacemaker Activity ◽  
Transmembrane Potentials ◽  
High K ◽  
Intracellular Microelectrodes ◽  
Simultaneous Decrease ◽  
Low K

The effects of changes in the extracellular concentrations of Ca, K and Mg on the transmembrane resting and action potentials of single fibers of the auricle, ventricle and specialized conducting system of the dog heart have been studied by means of intracellular microelectrodes. With respect to Ca, the three tissues exhibit quite different sensitivities. Changes in concentration of this ion alter the time course of the action potential recorded from auricle and ventricle but have little effect on the action potential configuration of the Purkinje fiber. In the latter tissue, on the other hand, pacemaker activity is most strongly enhanced by Ca depletion and excitability is lost at Ca concentrations permitting normal propagation in papillary muscle. The effect of K on the resting transmembrane potential is dependent on the simultaneous Ca concentration. The interrelationship is such that the depolarizing effect of high K is decreased by elevated Ca and the depolarization produced by low K is diminished by low levels of Ca. Changes in the concentration of Mg have little effect on the transmembrane potentials of cardiac muscle unless the level of Ca is low. Under this condition a simultaneous decrease in Mg gives rise to a marked prolongation of the action potential duration of both auricle and ventricle. Some evidence for the basic similarity of the processes underlying repolarization in these three tissues is presented and it is thought the normally encountered differences in their action potentials may be related to the sensitivity of each tissue to extracellular Ca.

scholarly journals Inotropic Effects of Trains of Impulses Applied during the Contraction of Cardiac Muscle

1960 ◽  
Vol 44 (2) ◽  
pp. 415-432 ◽  
Author(s):  
A. J. Brady ◽  
B. C. Abbott ◽  
W. F. H. M. Mommaerts
Keyword(s):  
Cell Membrane ◽  
Cardiac Muscle ◽  
Direct Effect ◽  
Refractory Period ◽  
Muscle Preparation ◽  
Inotropic Effects ◽  
Absolute Refractory Period ◽  
The Absolute ◽  
Stimulation Of

The application of a train of supramaximal stimuli during the absolute refractory period of a cardiac muscle preparation has two effects: a depression of the contraction during which it is applied, and a large potentiation of subsequent contractions. The former is ascribed to a direct effect upon the cell membrane, and is an indication of the continued control of the contractile event by this membrane. The latter is explained as a sudden liberation of norepinephrine by a stimulation of embedded nerve elements, which norepinephrine then distributes itself through the tissue and finally diffuses away.

Potentiation and intrinsic regulations in mammalian heart muscle

1964 ◽  
Vol 207 (5) ◽  
pp. 1123-1132 ◽  
Author(s):  
Antonio Bonnet Seoane
Keyword(s):  
Action Potential ◽  
Heart Muscle ◽  
Refractory Period ◽  
Action Potentials ◽  
Isometric Force ◽  
Electrical Response ◽  
Transmembrane Action Potentials ◽  
Mammalian Heart Muscle ◽  
Whole Muscle ◽  
Restitution Factor

Repeated paired stimuli (S1–S2) were applied to isolated atrial and ventricular preparations. Isometric force and transmembrane action potentials were recorded at different S1–S2 intervals. At the intervals where S2 evokes an action potential, developed force gradually attains a higher level during the S1–S2 train. This mechanical behavior is quantitatively dependent on the timing of S2. Potentiation is graded during the electrical relative refractory period and related to the amplitude of the premature electrical response. This relationship was confirmed under conditions of massive response, where propagation was suppressed and the whole muscle was activated at once. Potentiation can be augmented by interposing multiple (premature) action potentials between driven beats. By increasing the S1–S2 interval the premature contraction becomes evident and increases while the first one (driven) decreases. Mechanical events are delayed one cycle after the electrical ones. Three factors are proposed to account for the intrinsic inotropic regulation: a potentiating factor related to the action potential; an ionic compartment; and a restitution factor.

scholarly journals Control of action potential duration by calcium ions in cardiac Purkinje fibers.

1976 ◽  
Vol 67 (5) ◽  
pp. 599-617 ◽  
Author(s):  
R S Kass ◽  
R W Tsien
Keyword(s):  
Action Potential ◽  
Calcium Ions ◽  
Action Potentials ◽  
Cardiac Purkinje Fibers ◽  
Voltage Dependent ◽  
Two Factors ◽  
K Current ◽  
Ca Ions ◽  
Current Change ◽  
Plateau Level

It is well known that cardiac action potentials are shortened by increasing the external calcium concentration (Cao). The shortening is puzzling since Ca ions are thought to carry inward current during the plateau. We therefore studied the effects of Cao on action potentials and membrane currents in short Purkinje fiber preparations. Two factors favor the earlier repolarization. First, calcium-rich solutions generally raise the plateau voltage; in turn, the higher plateau level accelerates time- and voltage-dependent current changes which trigger repolarization. Increases in plateau height imposed by depolarizing current consistently produced shortening of the action potential. The second factor in the action of Ca ions involves iK1, the background K current (inward rectifier). Raising Cao enhances iK1 and thus favors faster repolarization. The Ca-sensitive current change was identified as an increase in iK1 by virtue of its dependence on membrane potential and Ko. A possible third factor was considered and ruled out: unlike epinephrine, calcium-rich solutions do not enhance slow outward plateau current, ikappa. These results are surprising in showing that calcium ions and epinephrine act quite differently on repolarizing currents, even though they share similar effects on the height and duration of the action potential.

scholarly journals Some Effects of Calcium Ions on the Action Potential of Single Nodes of Ranvier

1964 ◽  
Vol 48 (1) ◽  
pp. 113-127 ◽  
Author(s):  
Werner Ulbricht
Keyword(s):  
Action Potential ◽  
Calcium Ions ◽  
Refractory Period ◽  
Qualitative Agreement ◽  
Action Potentials ◽  
Outward Current ◽  
Nerve Fibers ◽  
Current Pulses ◽  
Delayed Rectification ◽  
Voltage Clamp Analysis

Action potentials of single frog nerve fibers were recorded with the air-gap method in "low Ca" (0.26 mM) and "high Ca" (4.2 mM) solutions and compared to spikes in normal Ringer's (1.05 mM Ca). On increasing (Ca)o the action potentials became shorter, the "knee" during the falling phase as well as the threshold for abolition moved to internal potentials more positive, and the spike recovery during the relative refractory period was faster. Outward current pulses applied during an action potential affected its configuration more in low Ca than in high Ca. The onset of the delayed rectification (in the absence of Na) was found faster in high Ga. After-potentials during anelectrotonus declined more rapidly in high Ca than in low Ca. The results are compared primarily with the voltage-clamp analysis of Ca effects on squid axons and satisfactory qualitative agreement is reached.

Interactions of area postrema and solitary tract in the nucleus tractus solitarius

1991 ◽  
Vol 260 (5) ◽  
pp. H1466-H1473 ◽  
Author(s):  
M. Hay ◽  
V. S. Bishop
Keyword(s):  
Action Potential ◽  
Neuronal Activity ◽  
Action Potentials ◽  
Nucleus Tractus Solitarius ◽  
Area Postrema ◽  
Rabbit Brain ◽  
Solitary Tract ◽  
Simultaneous Stimulation ◽  
Peripheral Afferents ◽  
Stimulation Of

The nucleus tractus solitarius (NTS) receives information from both area postrema (AP) and peripheral afferents. It is, therefore, one likely site of interaction between AP and peripheral afferent fibers. The present study's purpose was to determine the influence of AP stimulation on solitary tract-induced modulation of NTS neuronal activity. With the use of an in vitro rabbit brain slice preparation, extracellular recordings were made from 58 NTS neurons in which action potentials were evoked by both solitary tract and AP stimulation. In the majority of the cells tested, simultaneous stimulation of solitary tract and AP, at voltage levels that evoked no action potentials when stimulated separately, resulted in production of either single or multiple action potentials. In 27 units, stimulation levels to the solitary tract and to the AP were adjusted such that their respective separate stimulations produced an NTS action potential less than 30% of the time. When the two inputs were stimulated together, simultaneous stimulations produced an NTS action potential 100% of the time, suggesting a facilitatory interaction between the AP and the solitary tract on NTS neuronal activity. In nine cells, perfusion of the slice with clonidine induced a facilitation of solitary tract-evoked NTS response to a level similar to that seen during simultaneous stimulation of the solitary tract with the AP. Application of the alpha 2-adrenergic receptor antagonist yohimbine blocked the ability of both clonidine and AP to facilitate the solitary tract-evoked response. These results support a possible interaction between AP and peripheral afferents and suggest that AP stimulation facilitates effects of solitary tract activation at the level of the NTS.

Prolongation and shortening of action potentials by electrical shocks in frog ventricular muscle

1994 ◽  
Vol 266 (6) ◽  
pp. H2348-H2358 ◽  
Author(s):  
S. B. Knisley ◽  
W. M. Smith ◽  
R. E. Ideker
Keyword(s):  
Action Potential ◽  
Action Potentials ◽  
Maximum Rate ◽  
Transmembrane Potential ◽  
Ventricular Muscle ◽  
Intracellular Action Potential ◽  
Electrical Shocks ◽  
Intracellular Action ◽  
Maximum Rate Of Rise ◽  
Diastolic Potential

Effects of electrical shocks on myocardium are important for defibrillation. We measured effects of shocks (5 ms, 1–40 V/cm) in isolated frog ventricular strips. We recorded contraction strength and intracellular action potential (AP) with a shock-voltage cancellation technique to allow recordings immediately after shocks. Shocks of > or = 5 V/cm produced a dose- and latency-dependent prolongation of the AP ongoing during the shock. Stronger shocks of 28–40 V/cm decreased the duration, maximum diastolic potential, amplitude, and maximum rate of rise of the phase zero depolarization of paced APs that began after the shock. The contraction strength increased 43 and 59% during the 10 s after the stronger shocks. The transmembrane potential was shifted toward 0 mV immediately after the stronger shocks. We concluded that weak or strong shocks prolong the AP ongoing during the shock, whereas sufficiently strong shocks also shorten APs that begin after the shock. AP prolongation and shortening may be important for defibrillation and acceleration of tachycardia after failed cardioversion shocks.

Dependence of Intracellular End-Plate Action Potential on Adjacent Fiber Activity

1956 ◽  
Vol 187 (1) ◽  
pp. 199-202 ◽  
Author(s):  
Dexter M. Easton
Keyword(s):  
Action Potential ◽  
Action Potentials ◽  
Rana Pipiens ◽  
End Plate ◽  
Lower Maximum ◽  
The Difference ◽  
Adductor Longus ◽  
Intracellular Action ◽  
Stimulation Of

Intracellular action potentials were recorded at the end plate and 1 mm away from it in small bundles of m. adductor longus of Rana pipiens during stimulation of the nerve. The end-plate spike reached a lower maximum and the repolarization was slower when compared with the spikes recorded 1 mm away. The difference was of the form expected from externally recorded impulses, and was much diminished when the number of fibers was reduced to two to three. It is suggested that asynchrony of the activity in adjacent fibers explains the lesser distortion of action potentials distant from the end plate.

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