Anodal Excitation of Cardiac Muscle

1957 ◽  
Vol 190 (2) ◽  
pp. 383-390 ◽  
Author(s):  
Paul F. Cranefield ◽  
Brian F. Hoffman ◽  
Arthur A. Siebens
Keyword(s):  
Cardiac Muscle ◽  
Refractory Period ◽  
Ventricular Myocardium ◽  
Relative Refractory Period ◽  
Double Origin ◽  
Cathodal Stimulation

The strength-interval curve of dog ventricular myocardium has been measured with anodal and cathodal stimulation. During diastole the anodal threshold is higher than the cathodal. As anodal stimuli are applied progressively earlier the anodal threshold first rises above and then falls to levels below the anodal diastolic threshold. During most of the relative refractory period the anodal threshold is lower than the cathodal threshold. At all times during the late relative refractory period and throughout diastole excitation of double origin (anodal and cathodal) is evoked by sufficiently strong stimuli; this simultaneous origin of excitation at two points does not evoke fibrillation. During the early relative refractory period, however, only the anode is able to excite. Differences between anodal and cathodal thresholds are not attributable to asynchronous repolarization at the two electrode sites. The ‘no-response’ phenomenon occurs only when the anodal threshold is markedly lower than the cathodal.

scholarly journals Myosin types and fiber types in cardiac muscle. I. Ventricular myocardium.

1981 ◽  
Vol 88 (1) ◽  
pp. 226-233 ◽  
Author(s):  
S Sartore ◽  
L Gorza ◽  
S Pierobon Bormioli ◽  
L Dalla Libera ◽  
S Schiaffino
Keyword(s):  
Left Ventricle ◽  
Right Ventricle ◽  
Cardiac Muscle ◽  
Muscle Fibers ◽  
Ventricular Myocardium ◽  
Rabbit Heart ◽  
Fiber Types ◽  
Ventricular Muscle ◽  
The Right ◽  
Atrial Myosin

Antisera against bovine atrial myosin were raised in rabbits, purified by affinity chromatography, and absorbed with insolubilized ventricular myosin. Specific anti-bovine atrial myosin (anti-bAm) antibodies reacted selectively with atrial myosin heavy chains, as determined by enzyme immunoassay combined with SDS-gel electrophoresis. In direct and indirect immunofluorescence assay, anti-bAm was found to stain all atrial muscle fibers and a minor proportion of ventricular muscle fibers in the right ventricle of the bovine heart. In contrast, almost all muscle fibers in the left ventricle were unreactive. Purkinje fibers showed variable reactivity. In the rabbit heart, all atrial muscle fibers were stained by anti-bAm, whereas ventricular fibers showed a variable response in both the right and left ventricle, with a tendency for reactive fibers to be more numerous in the right ventricle and in subepicardial regions. Diversification of fiber types with respect to anti-bAm reactivity was found to occur during late stages of postnatal development in the rabbit heart and to be influenced by thyroid hormone. All ventricular muscle fibers became strongly reactive after thyroxine treatment, whereas they became unreactive or poorly reactive after propylthiouracil treatment. These findings are consistent with the existence of different ventricular isomyosins whose relative proportions can vary according to the thyroid state. Variations in ventricular isomyosin composition can account for the changes in myosin Ca2+-activated ATPase activity previously observed in cardiac muscle from hyper- and hypothyroid animals and may be responsible for the changes in the velocity of contraction of ventricular myocardium that occur under these conditions. The differential distribution of ventricular isomyosins in the normal heart suggests that fiber types with different contractile properties may coexist in the ventricular myocardium.

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.

scholarly journals Influence of Trimetazidine on Refractory Period of Isolated Rat Cardiac Muscle

1987 ◽  
Vol 39 (Supplement) ◽  
pp. S18-S25
Author(s):  
Jiro Sugimoto ◽  
Seiichi Yuasa ◽  
Masayasu Suzuki ◽  
Mitsuhiro Nagata
Keyword(s):  
Cardiac Muscle ◽  
Refractory Period ◽  
Isolated Rat

scholarly journals Effects of volatile anesthetics on elastic stiffness in isometrically contracting ferret ventricular myocardium

2002 ◽  
Vol 92 (6) ◽  
pp. 2491-2500 ◽  
Author(s):  
Anna E. Bartunek ◽  
Victor A. Claes ◽  
Philippe R. Housmans
Keyword(s):  
Right Ventricular ◽  
Cardiac Muscle ◽  
Real Time ◽  
Phase Relationship ◽  
Volatile Anesthetics ◽  
Ventricular Myocardium ◽  
Elastic Stiffness ◽  
Papillary Muscles ◽  
Optimal Length ◽  
Cross Bridges

The effects of halothane, isoflurane, and sevoflurane on elastic stiffness, which reflects the degree of cross-bridge attachment, were studied in intact cardiac muscle. Electrically stimulated (0.25 Hz, 25°C), isometrically twitching right ventricular ferret papillary muscles ( n = 15) at optimal length ( L max) were subjected to sinusoidal length oscillations (40 Hz, 0.25– 0.50% of L maxpeak to peak). The amplitude and phase relationship with the resulting force oscillations was decomposed into elastic and viscous components of total stiffness in real time. Increasing extracellular Ca2+ concentration in the presence of anesthetics to produce peak force equal to control increased elastic stiffness during relaxation, which suggests a direct effect of halothane and sevoflurane on cross bridges.

Relative Refractory Period

2005 ◽  
Vol 14 (3) ◽  
pp. 249-250
Author(s):  
Mary G. Adams ◽  
Michele M. Pelter
Keyword(s):  
Refractory Period ◽  
Relative Refractory Period

The Repetitive Responses of Isolated Axons from the Crab, Carcinus Maenas

1966 ◽  
Vol 45 (3) ◽  
pp. 475-488
Author(s):  
R. A. CHAPMAN
Keyword(s):  
Refractory Period ◽  
Carcinus Maenas ◽  
Membrane Resistance ◽  
Physiological Solution ◽  
Response Frequency ◽  
Electrical Currents ◽  
Slowing Down ◽  
Relative Refractory Period ◽  
Repolarization Phase ◽  
Cathodal Current

1. A method is described that enables the electrical responses of motor axons isolated from the leg nerve of the crab Carcinus to be studied close to or at the site of imposed electrical currents, while this area is continuously bathed by physiological solution. 2. The three classes of repetitive responses originally described by Hodgkin (1948) have occurred during the present work and additional features of these responses have been described. 3. The results support Hodgkin's original thesis that the development of the spike generating mechanisms determine the response frequency during a repetitive response, but a progressive lengthening of the relative refractory period occurs during this response and is considered to be the agency that causes the gradual slowing down of the response frequency, i.e. the adaption. 4. The processes of membrane restoration (repolarization and recovery) have been shown to be sensitive to applied currents; anodal current hastening and cathodal current slowing it. These phenomena provide a basis for interpreting the change in the duration of the relative refractory period observed during the repetitive response. 5. The differences between the form of the repetitive response in the crab axon and the predictions of the Hodgkin-Huxley equations is discussed and it seems likely that the rapid recovery of the membrane resistance during the repolarization phase of the crab axon action potential underlies this difference.

Refractory period response of cardiac Purkinje tissue to alpha 1- and alpha 2-adrenergic influences

1994 ◽  
Vol 267 (1) ◽  
pp. H376-H382 ◽  
Author(s):  
D. G. Cable ◽  
T. E. Rath ◽  
E. R. Dreyer ◽  
J. B. Martins
Keyword(s):  
Mean Arterial Pressure ◽  
Cell Membrane ◽  
Arterial Pressure ◽  
Refractory Period ◽  
Adrenergic Stimulation ◽  
Relative Refractory Period ◽  
Wb 4101 ◽  
Adrenergic Antagonists

Our purpose was to characterize Purkinje responses in vivo to alpha 1- and alpha 2-adrenergic stimulation in sinoaortically denervated and vagotomized dogs pretreated with metoprolol (1 mg/kg). We measured Purkinje relative refractory period (PRRP) responses to norepinephrine (NE) and phenylephrine (PE) with prazosin and/or yohimbine, WB-4101, and chloralethylclonidine (CEC) in varying doses. Results were as follows: PE infusion (25 micrograms.kg-1.min-1) prolonged PRRP (9.6 +/- 1.4 ms; a 4.1 +/- 0.4% change). Prazosin blocked PRRP prolongation with PE at 7 x 10(-8) M/kg (P < 0.05). Yohimbine did not attenuate PRRP prolongation with PE either alone or in combination with prazosin. NE infusion (0.8 micrograms.kg-1.min-1) also prolonged PRRP (9.2 +/- 2.3 ms; a 4.8 +/- 1.0% change). In contrast neither prazosin nor yohimbine at any dose (up to 10(-6) M/kg) totally blocked the prolongation with NE infusion. However, with prazosin (2 x 10(-7) M/kg) pretreatment, yohimbine blocked PRRP prolongation, significant at 7 x 10(-8) M/kg (P < 0.05). In separate experiments with yohimbine pretreatment at 7 x 10(-8) M/kg, PRRP prolongation with either PE or NE infusion was blocked equipotently with WB-4101 and CEC at 7 x 10(-8) M/kg. However, CEC did not block mean arterial pressure (MAP) responses to PE or NE infusion unlike WB-4101. We concluded that both subclasses of alpha 1-adrenergic antagonists equipotently block PRRP prolongation by alpha-agonists despite different effects on MAP. Purkinje refractoriness is also prolonged by alpha 2-adrenergic stimulation acting at the cell membrane.

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