Intracellular sodium ion activity: reliable measurement and stimulation-induced change in cardiac Purkinje fibers

1987 ◽  
Vol 65 (5) ◽  
pp. 954-962 ◽  
Author(s):  
Chin O. Lee ◽  
Wook B. Im ◽  
Jong K. Sonn
Keyword(s):  
Membrane Potential ◽  
Time Constant ◽  
Fast Response ◽  
Intracellular Sodium ◽  
Sodium Ion ◽  
Sodium Influx ◽  
Stimulation Rate ◽  
Purkinje Fibers ◽  
Cardiac Purkinje Fibers ◽  
Ion Activity

Recently Na+-selective microelectrodes (NaSM) have been used to measure quantitatively small changes in intracellular sodium ion activity [Formula: see text] and to determine a precise time course of comparatively rapid change in [Formula: see text]. In such studies, accurate measurement of [Formula: see text] requires the following criteria: (i) NaSM should have a fast response time and (ii) an NaSM and a conventional voltage microelectrode should measure the same membrane potential. These criteria were evaluated by measuring [Formula: see text] when membrane potential of cardiac Purkinje fibers was suddenly hyperpolarized and depolarized by changing stimulation rate. The NaSM coated with a conductive silver paint had fast response times so that rapid changes in [Formula: see text] could be reliably measured. The cardiac Purkinje fibers stimulated at a constant rate generated uniform membrane voltage and the NaSM and conventional microelectrode measured virtually the same membrane potential. This result is somewhat different from that reported under voltage-clamp condition by other investigators. The [Formula: see text] of the fibers increased as the stimulation rate was increased over the range of 0.5–3 Hz. In fibers stimulated at 1 Hz, cessation of stimulation was immediately followed by an exponential decline of [Formula: see text] with an average time constant of 53 ± 9 s (SD, n = 8), or rate constant of 0.020 ± 0.004/s. Restimulation of the fibers produced an exponential rise of [Formula: see text] with an average time constant of 65 ± 12 s (n = 8). Similar results were obtained in fibers stimulated at 2 Hz. The average rates of rise of [Formula: see text] after the onset of stimulations at 1 and 2 Hz were 1.0 and 1.5 mM/min, equivalent to increments in net sodium influx of 13.2 and 19.8 pmol∙cm−2∙s−1, respectively. The average maximum rate of [Formula: see text] rise produced by the application of 10−5 M strophanthidin to the fibers stimulated at 1 Hz was 1.3 ± 0.5 mM/min, equivalent to a net sodium influx of 17.2 pmol∙cm−2∙s−1.

Modulation of intracellular Na+ activity and cardiac force by norepinephrine and Ca2+

1983 ◽  
Vol 244 (1) ◽  
pp. C110-C114 ◽  
Author(s):  
C. O. Lee ◽  
M. Vassalle
Keyword(s):  
Contractile Force ◽  
Intracellular Sodium ◽  
Sodium Ion ◽  
Purkinje Fibers ◽  
Intracellular Na Activity ◽  
Cardiac Purkinje Fibers ◽  
High Calcium ◽  
Ion Activity ◽  
Ion Activities ◽  
Stimulation Of

The actions of norepinephrine and high calcium on the electrical, mechanical, and intracellular sodium ion activities were studied in electrically driven canine cardiac Purkinje fibers under different conditions. It was found that norepinephrine and high calcium decrease intracellular sodium ion activity (aiNa). The exposure to either agent is followed by a transient decline of force that correlates with the lower aiNa. Inhibition of the Na+ -K+ pump by strophanthidin reduces or abolishes the decrease in aiNa by norepinephrine but not that by high calcium. It is concluded that norepinephrine and high calcium both decrease aiNa and thereby the contractile force but (unlike high calcium) norepinephrine acts through the stimulation of the Na+ -K+ pump.

scholarly journals The relationship among intracellular sodium activity, calcium, and strophanthidin inotropy in canine cardiac Purkinje fibers.

1984 ◽  
Vol 83 (2) ◽  
pp. 287-307 ◽  
Author(s):  
M Vassalle ◽  
C O Lee
Keyword(s):  
Action Potential ◽  
Calcium Influx ◽  
Intracellular Sodium ◽  
Sodium Ion ◽  
Inotropic Effect ◽  
Similar Time ◽  
Tension Development ◽  
Purkinje Fibers ◽  
Cardiac Purkinje Fibers ◽  
High Calcium

The role of sodium and calcium ions in strophanthidin inotropy was studied by measuring simultaneously the electrical, mechanical, and intracellular sodium ion activities in electrically driven cardiac Purkinje fibers under conditions that change the intracellular sodium or calcium level (tetrodotoxin, strophanthidin, high calcium, and norepinephrine). Tetrodotoxin (TTX; 1-5 X 10(-6)M) shifted the action potential plateau to more negative values, shortened the action potential duration, and decreased the contractile tension and the intracellular sodium ion activity (aiNa). The changes in tension and in aiNa caused by TTX appear to be related since they had similar time courses. Strophanthidin (2-5 X 10(-7)M) increased tension and aiNa less in the presence of TTX, and, for any given value of aiNa, tension was less than in the absence of TTX. Increasing extracellular calcium (from 1.8 to 3.3-3.6 mM) or adding norepinephrine (0.5-1 X 10(-6)M) increased tension and decreased aiNa less in the presence than in the absence of TTX. When two of the above procedures were combined, the results were different. Thus, during the increase in aiNa and tension caused by strophanthidin in the presence of TTX, increasing calcium or adding norepinephrine increased tension markedly but did not increase aiNa further. In a TTX-high calcium or TTX-norepinephrine solution, adding strophanthidin increased both tension and aiNa, and the increase in tension was far greater than in the presence of TTX alone. The results indicate that: (a) the contractile force in Purkinje fibers is affected by a change in aiNa; (b) a decrease in aiNa by TTX markedly reduces the inotropic effect of strophanthidin, possibly as a consequence of depletion of intracellular calcium; (c) increasing calcium influx with norepinephrine or high calcium in the TTX-strophanthidin solution produces a potentiation of tension development, even if aiNa does not increase further; and (d) when the calcium influx is already increased by high calcium or norepinephrine, strophanthidin has its usual inotropic effect even in the presence of TTX. In conclusion, the positive inotropic effect of strophanthidin requires that an increase in aiNa be associated with suitable calcium availability.

The interrelationship of cesium, intracellular sodium activity, and pacemaker potential in cardiac Purkinje fibers

1990 ◽  
Vol 68 (9) ◽  
pp. 1236-1246 ◽  
Author(s):  
Giovanni Iacono ◽  
Mario Vassalle
Keyword(s):  
Membrane Potential ◽  
Intracellular Sodium ◽  
Resting Potential ◽  
Pacemaker Current ◽  
Purkinje Fibers ◽  
Sodium Activity ◽  
Diastolic Depolarization ◽  
Cardiac Purkinje Fibers ◽  
Myocardial Fibers

The actions of cesium (Cs) on intracellular sodium activity [Formula: see text], membrane potentials, and force were studied in sheep cardiac Purkinje and myocardial fibers superfused in vitro. In Purkinje fibers, Cs (2 mM) decreased diastolic depolarization, [Formula: see text] (−6.7%, p < 0.005), and force (−28.0%, p < 0.01). The effects of 4 and 8 mM Cs were more pronounced. In quiescent fibers, Cs (2–4 mM) also decreased [Formula: see text] (−17.3%, p < 0.005) and induced an initial hyperpolarization (+5.6 ± 1.3%, p < 0.005) followed by a return toward control. Diastolic depolarization was almost abolished by driving the fibers at 180/min (diastole was very short) but still Cs decreased [Formula: see text] (−15.4%). Tetrodotoxin decreased [Formula: see text] (−16.2%, p < 0.025) and reduced the Cs-induced fall in [Formula: see text] (−2.2%, p < 0.05). In zero [K]o, Cs decreased [Formula: see text] and caused repolarization. In 0.1 mM strophanthidin, Cs did not decrease [Formula: see text] any longer and affected the membrane potential little. In quiescent myocardial fibers, Cs (4 mM) decreased [Formula: see text] (−12.6%, p < 0.05) and transiently hyperpolarized (+2.1%). Rubidium (2 mM) decreased [Formula: see text] and resting potential in Purkinje fibers and in myocardial fibers and also decreased diastolic depolarization in Purkinje fibers. Thus, cesium and rubidium decrease [Formula: see text] and modify the membrane potential but not through a block of the inward pacemaker current If.Key words: rubidium, intracellular sodium activity, diastolic depolarization, tetrodotoxin, strophanthidin.

Quantitative relation of twitch and tonic tensions to intracellular Na+ activity in cardiac Purkinje fibers

1984 ◽  
Vol 247 (5) ◽  
pp. C478-C487 ◽  
Author(s):  
W. B. Im ◽  
C. O. Lee
Keyword(s):  
Membrane Potential ◽  
Linear Functions ◽  
Quantitative Relation ◽  
Purkinje Fibers ◽  
Average Value ◽  
Intracellular Na Activity ◽  
Cardiac Purkinje Fibers ◽  
Ion Activities ◽  
Model Equations ◽  
Low K

Quantitative relation of twitch and tonic tensions to intracellular Na ion was studied by describing model equations and measuring simultaneously the electrical, mechanical, and intracellular Na ion activities in electrically driven cardiac Purkinje fibers exposed to strophanthidin, tetrodotoxin (TTX), and varied [K+]0. In each experiment a plot of tension (T) vs. intracellular Na ion activity (aiNa) on logarithmic coordinates showed a good fit of the data to a single line described by the equation of T = beta (aiNa) gamma, in which beta and gamma represent the intercept and slope of the log T-log aiNa relation. Implication and average values of beta were presented. The average value of gamma obtained was 6.1 +/- 0.9 (SD, n = 8) in the experiments with strophanthidin (5 X 10(-7) - 10(-6) M) that somewhat depolarized transmembrane potential (Vm). The gamma value was 6.6 +/- 1.4 (n = 6) in the experiments with TTX (10(-6) - 5 X 10(-6) M) that shortened action potential duration. The gamma of 4.3 +/- 0.7 (n = 5) and 4.0 +/- 0.5 (n = 6) were obtained with the low [K+]0 of 1.0 and 2.0 mM, respectively, that hyperpolarized diastolic membrane potential by 12.7 +/- 6.3 mV (n = 5) and 13.7 +/- 2.4 mV (n = 6). The gamma value was 7.0 +/- 1.7 (n = 10) in the experiments with 8.1 mM [K+]0 that depolarized diastolic potential by 10.8 +/- 1.4 mV (n = 10). K+-free solution resulted in the gamma values of 6.0 +/- 0.9 (n = 6) for the twitch-aiNa relation and 5.3 +/- 1.4 (n = 9) for the tonic tension-aiNa relation. Except the experiments with the low [K+]0 the gamma values obtained are reasonably close to the value of 6.0 that is given on the basis of the 3Na-1Ca exchange and Ca2+-tension relation. In the experiments with the low [K+]0, the gamma values lower than 6.0 may be explained by the large hyperpolarization of diastolic membrane potential that could reduce intracellular calcium by means of the Na-Ca exchange. In conclusion, aiNa is a powerful determinant of twitch and tonic tensions which, in most instances, are linear functions of (aiNa)approximately 6.

scholarly journals Effect on Membrane Potential and Electrical Activity of Adding Sodium to Sodium-Depleted Cardiac Purkinje Fibers

1974 ◽  
Vol 64 (4) ◽  
pp. 473-493 ◽  
Author(s):  
Jay R. Wiggins ◽  
Paul F. Cranefield
Keyword(s):  
Membrane Potential ◽  
Electrical Activity ◽  
Resting Potential ◽  
Average Increase ◽  
Purkinje Fibers ◽  
Cardiac Purkinje Fibers ◽  
Sodium Extrusion

Canine cardiac Purkinje fibers exposed to Na-free solutions containing 128 mM TEA and 16 mM Ca show resting potentials in the range -50 to -90 mV; if the concentration of Na in the perfusate is raised from 0 to 4 to 24 mM, hyperpolarization follows. If the initial resting potential is low, the hyperpolarization tends to be greater; the average increase in the presence of 8 mM Na is 14 mV. Such hyperpolarization is not induced by adding Na to K-free solutions, is not seen in cooled fibers, or in fibers exposed to 10-3 M ouabain, nor is it induced by adding Li and thus may result from electrogenic sodium extrusion. Fibers exposed to Na-free solutions are often spontaneously active; if they are quiescent they often show repetitive activity during depolarizing pulses. Such spontaneous or repetitive activity is suppressed by the addition of Na. This suppression may or may not be related to the hyperpolarization.

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