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Two Inward Currents in Frog Atrial Muscle

Two Inward Currents in Frog Atrial Muscle The double sucrose-gap voltage-clamp technique was applied to frog atrial tissue to investigate the ionic currents responsible for the action potential in this tissue. Membrane depolarization elicited two distinct components of inward current when the test node was exposed to normal Ringer solution: a fast inward current and a slow inward current. The fast inward current appeared to be carried by sodium ions, since it was rapidly abolished by exposure of the fiber to Na + -free solution or tetrodotoxin but persisted on exposure to Ca ++ -free solution. In contrast, in the majority of the preparations the slow inward current appeared to be primarily carried by calcium ions, since it was abolished on exposure of the fiber to Ca ++ -free solution but persisted on exposure to Na + -free solution. Action potential data supported the voltage-clamp findings. The normal action potential shows two distinct components in the upstroke phase: an initial rapid phase of depolarization followed by a slower phase of depolarization reaching the peak of the action potential. Abolition of the fast inward current resulted in abolition of the initial rapid phase of depolarization. Abolition of the slow inward current resulted in abolition of the slow phase of depolarization. These data support the hypothesis that two distinct and different ionic mechanisms contribute to the upstroke phase of the action potential in frog atrial tissue. Footnotes Submitted: 1 April 1971 http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png The Journal of General Physiology Rockefeller University Press

Two Inward Currents in Frog Atrial Muscle

Tarr, Merrill
The Journal of General Physiology , Volume 58 (5): 523 – Nov 1, 1971
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References (20)

Publisher
Rockefeller University Press
Copyright
© 1971 Rockefeller University Press
ISSN
0022-1295
eISSN
1540-7748
DOI
10.1085/jgp.58.5.523
Publisher site
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Abstract

The double sucrose-gap voltage-clamp technique was applied to frog atrial tissue to investigate the ionic currents responsible for the action potential in this tissue. Membrane depolarization elicited two distinct components of inward current when the test node was exposed to normal Ringer solution: a fast inward current and a slow inward current. The fast inward current appeared to be carried by sodium ions, since it was rapidly abolished by exposure of the fiber to Na + -free solution or tetrodotoxin but persisted on exposure to Ca ++ -free solution. In contrast, in the majority of the preparations the slow inward current appeared to be primarily carried by calcium ions, since it was abolished on exposure of the fiber to Ca ++ -free solution but persisted on exposure to Na + -free solution. Action potential data supported the voltage-clamp findings. The normal action potential shows two distinct components in the upstroke phase: an initial rapid phase of depolarization followed by a slower phase of depolarization reaching the peak of the action potential. Abolition of the fast inward current resulted in abolition of the initial rapid phase of depolarization. Abolition of the slow inward current resulted in abolition of the slow phase of depolarization. These data support the hypothesis that two distinct and different ionic mechanisms contribute to the upstroke phase of the action potential in frog atrial tissue. Footnotes Submitted: 1 April 1971

Journal

The Journal of General Physiology – Rockefeller University Press

Published: Nov 1, 1971

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