Extracellular potentials related to intracellular action potentials during impulse conduction in anisotropic canine cardiac muscle.

Intracellular action potentials from normal, control nondystrophic and dystrophic mouse soleus muscle fibers were recorded in both voltage-time and phase-portrait plots. Flattening of a normally curved portion in certain dystrophic muscle-fiber phase portraits suggested a greater than usual secondary entry of sodium ions after the peak of the action potential. Low-chloride studies excluded an abnormal chloride current as the cause of the flattening. It appears that inactivation of sodium ion conductance may be delayed or reduced, or both, in certain fibers of mice with hereditary muscular dystrophy. This is consistent with a general increase in membrane permeability. No definite negative afterpotential was noted in most mouse muscle-fiber action potentials.

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Propagation of Action Potentials and the Structure of the Nexus in Cardiac Muscle

The Journal of General Physiology ◽

10.1085/jgp.48.5.797 ◽

1965 ◽

Vol 48 (5) ◽

pp. 797-823 ◽

Cited By ~ 321

Author(s):

L. Barr ◽

M. M. Dewey ◽

W. Berger

Keyword(s):

Guinea Pig ◽

Cardiac Muscle ◽

Action Potentials ◽

Structural Changes ◽

Sucrose Solution ◽

Electrical Coupling ◽

Intercalated Discs ◽

Sucrose Gap ◽

Specialized Structure ◽

Frog Atrium

The hypothesis that the nexus is a specialized structure allowing current flow between cell interiors is corroborated by concomitant structural changes of the nexus and changes of electrical coupling between cells due to soaking in solutions of abnormal tonicity. Fusiform frog atrial fibers are interconnected by nexuses. The nexuses, desmosomes, and regions of myofibrillar attachment of this muscle are not associated in a manner similar to intercalated discs of guinea pig cardiac muscle. Indeed, nexuses occur wherever cell membranes are closely apposed. Action potentials of frog atrial bundles detected extracellularly across a sucrose gap change from monophasic to diphasic when the gap is shunted by a resistor. This indicates that action potentials are transmitted across the gap when sufficient excitatory current is allowed to flow across the gap. When the sucrose solution in the gap is made hypertonic, propagation past the gap is blocked and the resistance between the cells in the gap increases. Electron micrographs demonstrate that the nexuses of frog atrium and guinea pig ventricle are ruptured by hypertonic solutions.

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Peripheral neural input to neurons of the middle cervical ganglion in the cat

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.1984.246.3.r354 ◽

1984 ◽

Vol 246 (3) ◽

pp. R354-R358

Author(s):

Z. J. Bosnjak ◽

J. P. Kampine

Keyword(s):

Electrical Stimulation ◽

Synaptic Input ◽

Action Potentials ◽

Efferent Nerve ◽

Neural Input ◽

Central Origin ◽

Cervical Ganglion ◽

Intracellular Action ◽

Peripheral Origin

In vitro studies were conducted on the middle cervical ganglion (MCG) of the cat by recording intracellular action potentials from its neurons. The purpose of this study was to examine the possibility of a peripheral synaptic input to the MCG. Preganglionic electrical stimulation, via the ventral ansa (VA) and dorsal ansa (DA) subclavia, and post-ganglionic electrical stimulation, via the ventrolateral cardiac nerve (VCN), evoked graded synaptic responses that led to the discharge of one or more action potentials in the 14 ganglia studied. The conduction velocity of these pathways ranged from 0.4 to 0.9 m/s. Ten percent of the cells impaled were inexcitable, even with direct intracellular depolarizing current, whereas 80% of the neurons studied received a synaptic input from fibers of both central and peripheral origin. In addition, subthreshold synaptic inputs from peripheral and central origin sum to discharge the cell, suggesting an integration of neural inputs in the MCG. These responses were blocked by d-tubocurarine chloride. This evidence indicates that sympathetic efferent nerve activity can be modified by peripheral excitatory inputs and that these inputs may function as pathways for a peripheral reflex at the level of the MCG.

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Effect of Several Cations on Transmembrane Potentials of Cardiac Muscle

American Journal of Physiology-Legacy Content ◽

10.1152/ajplegacy.1956.186.2.317 ◽

1956 ◽

Vol 186 (2) ◽

pp. 317-324 ◽

Cited By ~ 140

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.

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