Tetrodotoxin-sensitive component in action potential plateau of guinea pig Purkinje fibers: Comparison with the papillary muscle

1989 ◽  
Vol 20 (6) ◽  
pp. 791-797 ◽  
Author(s):  
Masahiro Aomine
Keyword(s):  
Guinea Pig ◽  
Action Potential ◽  
Papillary Muscle ◽  
Purkinje Fibers ◽  
Action Potential Plateau ◽  
Potential Plateau

Transmembrane potential changes caused by shocks in guinea pig papillary muscle

1996 ◽  
Vol 271 (6) ◽  
pp. H2536-H2546 ◽  
Author(s):  
X. Zhou ◽  
W. M. Smith ◽  
D. L. Rollins ◽  
R. E. Ideker
Keyword(s):  
Guinea Pig ◽  
Action Potential ◽  
Transmembrane Potential ◽  
Potential Gradient ◽  
Resting Potential ◽  
Na Channels ◽  
Action Potential Plateau ◽  
Potential Gradients ◽  
The Relationship ◽  
Potential Plateau

To study transmembrane potential (Vm) changes (delta Vm) caused by extracellular field stimulation, Vm was recorded in 10 guinea pig papillary muscles by a double-barrel microelectrode. A 10-ms shock was delivered during the action potential plateau or during diastole. Six shock strengths (1.8 +/- 0.4, 3.8 +/- 0.7, 5.6 +/- 0.9, 7.2 +/- 1.1, 11.1 +/- 1.9, and 17.8 +/- 1.5 V/cm) were given with both polarities. The tissue was then treated with either 30 microM tetrodotoxin (TTX; n = 5) or 30 microM TTX plus Ca(2+)-free (n = 5) perfusion. For shocks during the action potential plateau, delta Vm caused by the six potential gradients was 22.4 +/- 9.6, 43.6 +/- 17.4, 54.7 +/- 17.9, 60.4 +/- 18.1, 65.4 +/- 13.7, and 66.4 +/- 12.2 mV for shocks causing depolarization and 41.1 +/- 16.5, 68.3 +/- 22, 80.5 +/- 20.4, 84.0 +/- 19.5, 93.6 +/- 16.3, and 98.9 +/- 15.4 mV for shocks causing hyperpolarization. The relationship between delta Vm and shock potential gradient was not linear. During diastole, hyperpolarizing shocks induced initial hyperpolarization, then depolarization followed again by hyperpolarization. A new depolarization upstroke occurred immediately after the shock. After TTX or TTX plus Ca(2+)-free perfusion, point stimuli 10 times diastolic threshold could not induce an action potential, but a shock field of 1.8 +/- 0.2 V/cm still induced action potentials. The peak value of depolarization measured with respect to resting potential (-87 +/- 5 mV) during the hyperpolarizing shock decreased from +14 +/- 22 before to -66 +/- 30 mV with TTX perfusion (P < 0.01). The fast upstroke rate of depolarization both during and immediately after the end of hyperpolarizing shocks was inhibited by TTX perfusion. Thus 1) the relationship between delta Vm and shock potential gradient is not linear; 2) field but not point stimulation can induce an action potential when Na+ channels are inactivated; and 3) during diastole Na+ channels are activated twice by a 10-ms hyperpolarizing shock, once during shock-induced hyperpolarization and again immediately after the end of the shock.

Transmembrane potential and force of contraction of the normal and potassium-deficient human atrial tissue in vitro

1969 ◽  
Vol 47 (12) ◽  
pp. 1015-1024 ◽  
Author(s):  
Kailash Prasad
Keyword(s):  
Action Potential ◽  
Action Potentials ◽  
Terminal Phase ◽  
Free Solution ◽  
Force Of Contraction ◽  
Pacemaker Cells ◽  
Atrial Tissue ◽  
Action Potential Plateau ◽  
Potential Plateau

The characteristics of the simultaneously recorded action potential (AP) and contraction of isolated atrial tissue of human heart were studied in normal and in potassium-free solutions. Two types of action potentials associated with characteristic contractions were observed. Pacemaker types of action potentials with two humps in the plateau were observed in spontaneously beating atria and they were associated with triple contractions. A non-pacemaker type of action potential was found in quiescent fibers when the preparation was driven electrically; this resulted in single peak contraction. The sizes of the resting and action potentials of pacemaker cells were lower, while those of action potential duration in all types of cells were higher than those reported in other mammals. When spontaneously beating atrial pieces were exposed to a potassium-free solution there was a shortening of the action potential plateau and lengthening of the terminal phase of repolarization associated with the development of the first hump into a slow spike. The shortening of the action potential plateau associated with an increase in the force of contraction was also observed in electrically stimulated muscles in KCl-free solution.

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