scholarly journals Maximum Rate of Depolarization of Single Muscle Fiber in Normal and Low Sodium Solutions

1965 ◽  
Vol 49 (1) ◽  
pp. 17-25 ◽  
Author(s):  
Arnaldo Ferroni ◽  
Donatella Blanchi
Keyword(s):  
Action Potentials ◽  
Maximum Rate ◽  
Sodium Current ◽  
Sodium Concentration ◽  
Single Muscle ◽  
Membrane Action ◽  
Independence Principle ◽  
Low Sodium ◽  
Intracellular Microelectrodes ◽  
Normal Tyrode Solution

The values of membrane action potentials and maximum depolarization rates of single muscle fibers in normal Tyrode solution and in low sodium solutions containing as little as 20 per cent of the sodium chloride were measured with intracellular microelectrodes. Under these conditions the membrane potential remains unchanged up to 36 per cent of [Na+]out concentration, whereas the overshoot of the action potential varies linearly with the logarithm of the external sodium concentration. The maximum depolarization rate is a linear function of the external sodium concentration. The results obtained support the ionic theory for sodium and the independence principle for sodium current related to the external sodium concentration.

THE ELECTRICAL PROPERTIES OF THE SMOOTH MUSCLE CELL MEMBRANE

1958 ◽  
Vol 36 (9) ◽  
pp. 959-975 ◽  
Author(s):  
E. E. Daniel ◽  
H. Singh
Keyword(s):  
Smooth Muscle ◽  
Electrical Properties ◽  
Action Potential ◽  
Action Potentials ◽  
Maximum Rate ◽  
Sodium Current ◽  
Choline Chloride ◽  
Total Duration ◽  
Smooth Muscles ◽  
Sodium Concentration

In myometrium from pregnant cat, repetitive action potentials have been recorded during contraction. Using intracellular electrodes the depolarizations averaged 35 mv. Maximum rate of depolarization was 1–2 v/sec and the action potential duration varied from 250 milliseconds to much longer periods. Membrane reversal of up to 10 mv sometimes occurred. Total resistance decreased during depolarization and recovered during repolarization. Typical biphasic potentials were also recorded with extracellular electrodes. Their amplitude (peak to peak) varied from 0.3 to several millivolts and their duration (peak to peak) from 10–40 milliseconds. Reduction of external sodium concentration to as little as one-ninth normal (choline chloride or sucrose replacement) did not reduce the amplitudes of the resting or action potentials measured intracellularly or extracellularly, but decreased the action potential frequency. Membrane reversal still occurred with intracellular electrodes and the maximum rate of depolarization was unchanged. The rate of repolarization was increased so that the total duration of the action potential was 150 to 200 milliseconds. With extracellular electrodes, the peak to peak amplitudes were increased and the durations were unchanged. Further reduction of external sodium concentration to less than 15–20 meq/liter caused a contraction without further change in action potential configuration. Gradual relaxation and slowing of the repetition rate of action potentials occurred and resulted eventually in complete mechanical and electrical inactivity.Rabbit taenia coli were also studied and their electrical properties contrasted to those of cat myometrium. The conclusions were reached that: (1) the available evidence opposes the hypotheses that an inward sodium current accounts for depolarization in smooth muscle and (2) smooth muscles differed in their electrical properties and mechanisms of ion distribution not only from striate muscles but also from one another.

THE ELECTRICAL PROPERTIES OF THE SMOOTH MUSCLE CELL MEMBRANE

1958 ◽  
Vol 36 (1) ◽  
pp. 959-975 ◽  
Author(s):  
E. E. Daniel ◽  
H. Singh
Keyword(s):  
Smooth Muscle ◽  
Electrical Properties ◽  
Action Potential ◽  
Action Potentials ◽  
Maximum Rate ◽  
Sodium Current ◽  
Choline Chloride ◽  
Total Duration ◽  
Smooth Muscles ◽  
Sodium Concentration

In myometrium from pregnant cat, repetitive action potentials have been recorded during contraction. Using intracellular electrodes the depolarizations averaged 35 mv. Maximum rate of depolarization was 1–2 v/sec and the action potential duration varied from 250 milliseconds to much longer periods. Membrane reversal of up to 10 mv sometimes occurred. Total resistance decreased during depolarization and recovered during repolarization. Typical biphasic potentials were also recorded with extracellular electrodes. Their amplitude (peak to peak) varied from 0.3 to several millivolts and their duration (peak to peak) from 10–40 milliseconds. Reduction of external sodium concentration to as little as one-ninth normal (choline chloride or sucrose replacement) did not reduce the amplitudes of the resting or action potentials measured intracellularly or extracellularly, but decreased the action potential frequency. Membrane reversal still occurred with intracellular electrodes and the maximum rate of depolarization was unchanged. The rate of repolarization was increased so that the total duration of the action potential was 150 to 200 milliseconds. With extracellular electrodes, the peak to peak amplitudes were increased and the durations were unchanged. Further reduction of external sodium concentration to less than 15–20 meq/liter caused a contraction without further change in action potential configuration. Gradual relaxation and slowing of the repetition rate of action potentials occurred and resulted eventually in complete mechanical and electrical inactivity.Rabbit taenia coli were also studied and their electrical properties contrasted to those of cat myometrium. The conclusions were reached that: (1) the available evidence opposes the hypotheses that an inward sodium current accounts for depolarization in smooth muscle and (2) smooth muscles differed in their electrical properties and mechanisms of ion distribution not only from striate muscles but also from one another.

scholarly journals The Effect of High Sodium Concentration on the Action Potential of the Skate Heart

1967 ◽  
Vol 50 (3) ◽  
pp. 505-517 ◽  
Author(s):  
Issei Seyama ◽  
Hiroshi Irisawa
Keyword(s):  
Action Potential ◽  
Action Potentials ◽  
Sea Water ◽  
Least Squares Method ◽  
Sodium Concentration ◽  
High Sodium ◽  
Low Sodium ◽  
Other Substances ◽  
Almost All ◽  
High Sodium Concentration

It already has been well documented that the maximum rate of depolarization and amplitude of action potentials are directly dependent on [Na+]o in the vertebrate myocardium. Almost all studies have been carried out at low sodium concentration ranges by substituting NaCl for other substances. Action potentials should be demonstrable in higher sodium concentrations, but cells are inevitably damaged by osmotic changes. The blood of elasmobranchs is nearly isosmotic with sea water, but NaCl accounts for 54.5% of the osmotic pressure and 38.7% of it is maintained by urea molecules. Utilizing this special situation in elasmobranchs, the effect of high sodium concentration was studied up to 170% of normal sodium concentration, while still retaining isosmotic condition. The rate of depolarization, amplitude, and duration of the myocardial action potential all increased in direct proportion to [Na+]o, and no depressant effect on transmembrane action potentials was observed in solutions of high sodium concentration. With regard to depolarization rate, the regression curve fitted by the least squares method passed through zero within two standard errors. At high sodium levels, the overshoot changed as expected theoretically, but at lower ranges it deviated from the theoretical values. [Na+]i, and [K+]i, in this tissue have been determined, and these data are explained on the basis of the Na theory.

scholarly journals Potentiometric measurement of membrane action potentials in frog muscle fibres

1966 ◽  
Vol 183 (1) ◽  
pp. 152-166 ◽  
Author(s):  
B. Frankenhaeuser ◽  
B. D. Lindley ◽  
R. S. Smith
Keyword(s):  
Action Potentials ◽  
Frog Muscle ◽  
Muscle Fibres ◽  
Membrane Action ◽  
Potentiometric Measurement

scholarly journals Sodium Radiofrequency Coils for Magnetic Resonance: From Design to Applications

Electronics ◽  
2021 ◽  
Vol 10 (15) ◽  
pp. 1788
Author(s):  
Giulio Giovannetti ◽  
Alessandra Flori ◽  
Nicola Martini ◽  
Roberto Francischello ◽  
Giovanni Donato Aquaro ◽  
...  
Keyword(s):  
Magnetic Resonance ◽  
Sodium Concentration ◽  
Resonance Spectroscopy ◽  
Sodium Mri ◽  
Human Organs ◽  
Low Sodium ◽  
Radiofrequency Coils ◽  
Anatomical Imaging ◽  
Strong Gradient

Sodium (23Na) is the most abundant cation present in the human body and is involved in a large number of vital body functions. In the last few years, the interest in Sodium Magnetic Resonance Imaging (23Na MRI) has considerably increased for its relevance in physiological and physiopathological aspects. Indeed, sodium MRI offers the possibility to extend the anatomical imaging information by providing additional and complementary information on physiology and cellular metabolism with the heteronuclear Magnetic Resonance Spectroscopy (MRS). Constraints are the rapidly decaying of sodium signal, the sensitivity lack due to the low sodium concentration versus 1H-MRI induce scan times not clinically acceptable and it also constitutes a challenge for sodium MRI. With the available magnetic fields for clinical MRI scanners (1.5 T, 3 T, 7 T), and the hardware capabilities such as strong gradient strengths with high slew rates and new dedicated radiofrequency (RF) sodium coils, it is possible to reach reasonable measurement times (~10–15 min) with a resolution of a few millimeters, where it has already been applied in vivo in many human organs such as the brain, cartilage, kidneys, heart, as well as in muscle and the breast. In this work, we review the different geometries and setup of sodium coils described in the available literature for different in vivo applications in human organs with clinical MR scanners, by providing details of the design, modeling and construction of the coils.

The biphasic morphology of voluntary and spontaneous single muscle fiber action potentials

1994 ◽  
Vol 17 (11) ◽  
pp. 1301-1307 ◽  
Author(s):  
Daniel Dumitru ◽  
John C. King ◽  
William van der Rijt ◽  
Dick F. Stegeman
Keyword(s):  
Muscle Fiber ◽  
Action Potentials ◽  
Single Muscle ◽  
Single Muscle Fiber ◽  
Fiber Action

A role for a background sodium current in spontaneous action potentials and secretion from rat lactotrophs

1996 ◽  
Vol 271 (6) ◽  
pp. C1927-C1934 ◽  
Author(s):  
S. Sankaranarayanan ◽  
S. M. Simasko
Keyword(s):  
Action Potentials ◽  
Sodium Current ◽  
Plaque Assay ◽  
Input Resistance ◽  
Cytosolic Calcium ◽  
Calcium Dependent ◽  
Whole Cell Patch Clamp ◽  
Spontaneous Action ◽  
Spontaneous Action Potentials ◽  
Spontaneous Secretion

We have used the perforated-patch variation of whole cell patch-clamp techniques, measurements of cytosolic calcium with use of fura 2, and secretion measurements with use of the reverse-hemolytic plaque assay to address the role of depolarizing background currents in maintaining spontaneous action potentials and spontaneous secretion from rat lactotrophs in primary culture. Replacement of bath sodium with tris(hydroxymethyl)aminomethane or N-methyl-D-glucamine caused a dramatic hyperpolarization of the cells, a cessation of spontaneous action potentials, and an increase in input resistance of cells. Tetrodotoxin had no effect on spontaneous action potentials, and removal of bath calcium stopped spiking but did not hyperpolarize the cells. The hyperpolarization in response to removal of bath sodium was associated with a decrease in cytosolic calcium levels. Finally, removal of bath sodium caused a decrease in spontaneous secretion of prolactin from lactotrophs. These data suggest that a background sodium current is essential to drive the membrane to threshold for firing spontaneous calcium-dependent action potentials in lactotrophs. This, in turn, results in elevated intracellular calcium, which supports spontaneous secretion of prolactin from these cells.

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.

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