Effects of Sodium Pump Inhibition on Contraction in Sheep Cardiac Purkinje Fibers

1983 ◽  
pp. 885-890 ◽  
Author(s):  
D.A. Eisner ◽  
W.J. Lederer ◽  
R.D. Vaughan-Jones
Keyword(s):  
Sodium Pump ◽  
Purkinje Fibers ◽  
Cardiac Purkinje Fibers ◽  
Sodium Pump Inhibition

Acetylcholine increases intracellular sodium activity in sheep cardiac Purkinje fibers

1989 ◽  
Vol 256 (5) ◽  
pp. H1407-H1416
Author(s):  
G. Iacono ◽  
M. Vassalle
Keyword(s):  
Action Potential ◽  
Spontaneous Activity ◽  
Sodium Pump ◽  
Contractile Force ◽  
Intracellular Sodium ◽  
Resting Potential ◽  
Purkinje Fibers ◽  
Transmembrane Potentials ◽  
Sodium Activity ◽  
Cardiac Purkinje Fibers

The action of acetylcholine (ACh) on intracellular sodium activity (alpha iNa) was studied in sheep Purkinje fibers by means of a Na+-selective microelectrode technique while transmembrane potentials and contractile force were simultaneously recorded. In quiescent fibers, 10(-4) to 10(-5) M ACh shifted the resting potential to less negative values and increased alpha iNa from 5.57 +/- 0.21 to 6.45 +/- 0.35 mM (+15.8%, P less than 0.005). In other experiments, ACh induced a depolarization that initiated spontaneous activity. In fibers driven at 60 beats/min, ACh prolonged the action potential, increased alpha iNa from 7.98 +/- 0.15 to 9.36 +/- 0.3 mM (+17.29%, P less than 0.005), and increased contractile force. Norepinephrine (10(-5) to 10(-6) M) increased contractile force and decreased alpha iNa, but in its presence ACh still increased force and alpha iNa and vice versa. Strophanthidin (10(-4) M) increased alpha iNa, and 3 x 10(-6) M propranolol and 10(-6) M atropine decreased alpha iNa. Both strophanthidin and atropine (but not propranolol) prevented the increase in alpha iNa by ACh. It is concluded that the ACh increases alpha iNa and contractile force through the inhibition of the sodium pump and that these actions are due to the activation of the muscarinic receptor and not to endogenously released norepinephrine.

scholarly journals Electrogenic sodium extrusion in cardiac Purkinje fibers.

1979 ◽  
Vol 73 (6) ◽  
pp. 819-837 ◽  
Author(s):  
D C Gadsby ◽  
P F Cranefield
Keyword(s):  
Sodium Pump ◽  
Pump Current ◽  
Flow Chamber ◽  
Resting Potential ◽  
Pacemaker Activity ◽  
Free Fluid ◽  
Purkinje Fibers ◽  
Cardiac Purkinje Fibers ◽  
Fast Flow ◽  
K Depletion

Thin canine cardiac Purkinje fibers in a fast flow chamber were exposed to K-free fluid for 15 s to 6 min to initiate "sodium loading," then returned to K-containing fluid to stimulate the sodium pump. The electrophysiological effects of enhanced pump activity may result from extracellular K depletion caused by enhanced cellular uptake of K or from an increase in the current generated as a result of unequal pumped movements of Na and K, or from both. The effects of pump stimulation were therefore studied under three conditions in which lowering the external K concentration ([K]0) causes changes opposite to those expected from an increase in pump current. First, the resting potential of Purkinje fibers may have either a "high" value of a "low" (less negative) value: at the low level of potential, experimental reduction of [K]0 causes depolarization, whereas an increase in pump current should cause hyperpolarization. Second, in regularly stimulated Purkinje fibers, lowering [K]0 prolongs the action potential, whereas an increase in outward pump current should shorten it. Finally, lowering [K]0 enhances spontaneous "pacemaker" activity in Purkinje fibers, whereas an increase in outward pump current should reduce or abolish spontaneous activity. Under all three conditions, we find that the effects of temporary stimulation of the sodium pump are those expected from a transient increase in outward pump current, not those expected from K depletion.

Regulation of twitch tension in sheep cardiac Purkinje fibers during calcium overload

1987 ◽  
Vol 253 (6) ◽  
pp. H1540-H1547 ◽  
Author(s):  
J. R. Berlin ◽  
M. B. Cannell ◽  
W. J. Lederer
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Calcium Current ◽  
Calcium Release ◽  
Calcium Overload ◽  
Purkinje Fibers ◽  
Cellular Processes ◽  
Cardiac Purkinje Fibers ◽  
Sodium Pump Inhibition ◽  
Spontaneous Fluctuations ◽  
Oscillatory Period

The dependence of twitch tension on the interval (delta t) between depolarizations was examined in voltage-clamped sheep cardiac Purkinje fibers under conditions of calcium overload. During the development of calcium overload (produced by sodium-pump inhibition), twitch amplitude changes from a monotonic function of delta t to an oscillatory one. We investigated the cellular processes underlying this oscillatory relationship. Measurable calcium current was blocked by D 600 (25 microM), but neither the twitch nor the oscillatory dependence of twitch tension on delta t was abolished. Caffeine (2 mM), applied to modify sarcoplasmic reticulum function, decreased the oscillatory period of the twitch/interval relationship as it increased the frequency of spontaneous fluctuations of resting tension. Our results suggest that the oscillatory relationship between twitch amplitude and delta t is not caused by changes in the calcium current per se but rather by fluctuations in the amount of releasable calcium in the sarcoplasmic reticulum. Additionally, we conclude that the calcium current may not be a necessary prerequisite for depolarization to trigger calcium release from the sarcoplasmic reticulum under conditions of calcium overload.

Differential Effects of Halothane and Isoflurane on Contractile Force and Calcium Transients in Cardiac Purkinje Fibers

1994 ◽  
Vol 80 (6) ◽  
pp. 1360-1368 ◽  
Author(s):  
David F. Stowe ◽  
Juraj Sprung ◽  
Lawrence A. Turner ◽  
John P. Kampine ◽  
Zeljko J. Bosnjak
Keyword(s):  
Contractile Force ◽  
Calcium Transients ◽  
Purkinje Fibers ◽  
Differential Effects ◽  
Cardiac Purkinje Fibers

Inhibitory effects of catecholamines in canine cardiac Purkinje fibers

1976 ◽  
Vol 231 (5) ◽  
pp. 1415-1420 ◽  
Author(s):  
P Posner ◽  
EL Farrar ◽  
CR Lambert
Keyword(s):  
Negative Response ◽  
Chronotropic Effect ◽  
Inhibitory Effects ◽  
Purkinje Fibers ◽  
Spontaneous Rate ◽  
Negative Chronotropic Effect ◽  
Cardiac Purkinje Fibers ◽  
Wide Range ◽  
Low Levels

The effect of catecholamines over a wide range of concentrations was studied on 42K uptake and efflux, as well as on spontaneous rate in canine cardiac Purkinje fibers. Low levels of catecholamines (less than 10(-10) M epinephrine; less than 10(-9) M norepinephrine) decreased automaticity. This negative chronotropic effect was blocked by phentolamine and mimicked by phenylephrine. These low levels of epinephrine and norepinephrine also inhibited 42K uptake by Purkinje fibers but had no effect on 42K efflux. The inhibition of 42K uptake was blocked by phentolamine and verapamil and mimicked by phenylephrine. The data indicate an alpha-receptor-mediated negative response of rate and 42K uptake to low levels of catecholamine. The end result is discussed in terms of a competitive increase in the influx of Ca2+ rather than Na+ and an indirect inhibition of the Na+-K+ pump.

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