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Changes in Membrane Properties of Chick Embryonic Hearts during Development

Changes in Membrane Properties of Chick Embryonic Hearts during Development The electrophysiological properties of embryonic chick hearts (ventricles) change during development; the largest changes occur between days 2 and 8. Resting potential ( E m ) and peak overshoot potential (+ E max ) increase, respectively, from -35 mv and +11 mv at day 2 to -70 mv and +28 mv at days 12–21. Action potential duration does not change significantly. Maximum rate of rise of the action potential (+ V max ) increases from about 20 v/sec at days 2–3 to 150 v/sec at days 18–21; + V max of young cells is not greatly increased by applied hyperpolarizing current pulses. In resting E m vs. log K + o curves, the slope at high K + is lower in young hearts (e.g. 30 mv/decade) than the 50–60 mv/decade obtained in old hearts, but the extrapolated K + i values (125–140 m M ) are almost as high. Input resistance is much higher in young hearts (13 MΩ at day 2 vs. 4.5 MΩ at days 8–21), suggesting that the membrane resistivity ( R m ) is higher. The ratio of permeabilities, P Na / P K , is high (about 0.2) in young hearts, due to a low P K , and decreases during ontogeny (to about 0.05). The low K + conductance ( g K ) in young hearts accounts for the greater incidence of hyperpolarizing afterpotentials and pacemaker potentials, the lower sensitivity (with respect to loss of excitability) to elevation of K + o , and the higher chronaxie. Acetylcholine does not increase g K of young or old ventricular cells. The increase in (Na + , K + )-adenosine triphosphatase (ATPase) activity during development tends to compensate for the increase in g K . + E max and + V max are dependent on Na + o in both young and old hearts. However, the Na + channels in young hearts (2–4 days) are slow, tetrodotoxin (TTX)-insensitive, and activated-inactivated at lower E m . In contrast, the Na + channels of cells in older hearts (> 8 days) are fast and TTX-sensitive, but they revert back to slow channels when placed in culture. Footnotes Submitted: 5 January 1972 http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png The Journal of General Physiology Rockefeller University Press

Changes in Membrane Properties of Chick Embryonic Hearts during Development

The Journal of General Physiology , Volume 60 (4): 430 – Oct 1, 1972

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References (46)

Publisher
Rockefeller University Press
Copyright
© 1972 Rockefeller University Press
ISSN
0022-1295
eISSN
1540-7748
DOI
10.1085/jgp.60.4.430
Publisher site
See Article on Publisher Site

Abstract

The electrophysiological properties of embryonic chick hearts (ventricles) change during development; the largest changes occur between days 2 and 8. Resting potential ( E m ) and peak overshoot potential (+ E max ) increase, respectively, from -35 mv and +11 mv at day 2 to -70 mv and +28 mv at days 12–21. Action potential duration does not change significantly. Maximum rate of rise of the action potential (+ V max ) increases from about 20 v/sec at days 2–3 to 150 v/sec at days 18–21; + V max of young cells is not greatly increased by applied hyperpolarizing current pulses. In resting E m vs. log K + o curves, the slope at high K + is lower in young hearts (e.g. 30 mv/decade) than the 50–60 mv/decade obtained in old hearts, but the extrapolated K + i values (125–140 m M ) are almost as high. Input resistance is much higher in young hearts (13 MΩ at day 2 vs. 4.5 MΩ at days 8–21), suggesting that the membrane resistivity ( R m ) is higher. The ratio of permeabilities, P Na / P K , is high (about 0.2) in young hearts, due to a low P K , and decreases during ontogeny (to about 0.05). The low K + conductance ( g K ) in young hearts accounts for the greater incidence of hyperpolarizing afterpotentials and pacemaker potentials, the lower sensitivity (with respect to loss of excitability) to elevation of K + o , and the higher chronaxie. Acetylcholine does not increase g K of young or old ventricular cells. The increase in (Na + , K + )-adenosine triphosphatase (ATPase) activity during development tends to compensate for the increase in g K . + E max and + V max are dependent on Na + o in both young and old hearts. However, the Na + channels in young hearts (2–4 days) are slow, tetrodotoxin (TTX)-insensitive, and activated-inactivated at lower E m . In contrast, the Na + channels of cells in older hearts (> 8 days) are fast and TTX-sensitive, but they revert back to slow channels when placed in culture. Footnotes Submitted: 5 January 1972

Journal

The Journal of General PhysiologyRockefeller University Press

Published: Oct 1, 1972

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