Although cell shortening in patch-clamped cells (current-clamp mode)
is triggered by an ordinary action potential, the trigger mechanism
in field-stimulated cells is not so obvious. The contraction characteristics
of the two methods differ, and we, therefore, examined the triggering
sequence in field-stimulated cells. Isolated rat cardiomyocytes were
plated on laminin-coated coverslips that were mounted on an inverted
light microscope and superfused with HEPES-Tyrode buffer (pH 7.4;
37 degrees C). The cells were stimulated to contract either by a
0.5-ms current injection (CC cells) through high-resistance electrodes
or a 5-ms biphasic field-stimulation pulse (FS cells), and drugs
were added to block sarcolemmal proteins involved in excitation-contraction
coupling. Time to peak contraction (TTP) was significantly longer
in FS cells and was not affected by the polarity or the length
of the stimulus pulse. Tetrodotoxin (TTX; 20 microM) blocked cell
shortening in CC cells but not in FS cells. Ni$^2+$ (5 mM) blocked
cell shortening in FS cells, whereas KB-R7943 (KB; 5 microM)
had no effect either on cell shortening or TTP. In FS cells,
nifedipine (Nif; 100 microM) and Cd$^2+$ (300 microM) reduced
fractional
shortening by 34 and 63\%, respectively, but only Cd$^2+$ affected
TTP (reduced by 48\%). A combination of Nif and KB reduced cell
shortening by 50\%, whereas a combination of Cd$^2+$ and KB almost
abolished cell shortening. We conclude that field stimulation per
se prolongs TTP and that cell shortening in FS cells is not dependent
on Na$^+$ current but is triggered by a combination of L-type
Ca$^2+$
current and reverse mode Na$^+$/Ca$^2+$ exchange.
%0 Journal Article
%1 Boke_2005_1712
%A B�kenes, Janny
%A Sjaastad, Ivar
%A Sejersted, Ole M
%D 2005
%J J. Appl. Physiol.
%K 15640393 5-HT4, AMP, Agents, Agonists, Animals, Antagonists, Cardiac, Cardiotonic Cell Chain Comparative Concentration, Congestive, Contraction, Cyclic Failure, Fibroblasts, Gov't, Heart Hematoporphyrins, Humans, Hydrogen-Ion Indoles, Infarction, Line, Male, Membrane Mesoporphyrins, Messenger, Muscles, Myocardial Myocytes, Non-U.S. Papillary Photosensitizing Polymerase Porphyrins, Potentials, RNA, Rats, Reaction, Receptors, Research Reverse Serotonin Serotonin, Skin, Study, Sulfonamides, Support, Tetraethylammonium, Transcriptase Tumor, Wistar,
%N 5
%P 1712-9
%R 10.1152/japplphysiol.00630.2004
%T Artifactual contractions triggered by field stimulation of cardiomyocytes.
%U http://dx.doi.org/10.1152/japplphysiol.00630.2004
%V 98
%X Although cell shortening in patch-clamped cells (current-clamp mode)
is triggered by an ordinary action potential, the trigger mechanism
in field-stimulated cells is not so obvious. The contraction characteristics
of the two methods differ, and we, therefore, examined the triggering
sequence in field-stimulated cells. Isolated rat cardiomyocytes were
plated on laminin-coated coverslips that were mounted on an inverted
light microscope and superfused with HEPES-Tyrode buffer (pH 7.4;
37 degrees C). The cells were stimulated to contract either by a
0.5-ms current injection (CC cells) through high-resistance electrodes
or a 5-ms biphasic field-stimulation pulse (FS cells), and drugs
were added to block sarcolemmal proteins involved in excitation-contraction
coupling. Time to peak contraction (TTP) was significantly longer
in FS cells and was not affected by the polarity or the length
of the stimulus pulse. Tetrodotoxin (TTX; 20 microM) blocked cell
shortening in CC cells but not in FS cells. Ni$^2+$ (5 mM) blocked
cell shortening in FS cells, whereas KB-R7943 (KB; 5 microM)
had no effect either on cell shortening or TTP. In FS cells,
nifedipine (Nif; 100 microM) and Cd$^2+$ (300 microM) reduced
fractional
shortening by 34 and 63\%, respectively, but only Cd$^2+$ affected
TTP (reduced by 48\%). A combination of Nif and KB reduced cell
shortening by 50\%, whereas a combination of Cd$^2+$ and KB almost
abolished cell shortening. We conclude that field stimulation per
se prolongs TTP and that cell shortening in FS cells is not dependent
on Na$^+$ current but is triggered by a combination of L-type
Ca$^2+$
current and reverse mode Na$^+$/Ca$^2+$ exchange.
@article{Boke_2005_1712,
abstract = {Although cell shortening in patch-clamped cells (current-clamp mode)
is triggered by an ordinary action potential, the trigger mechanism
in field-stimulated cells is not so obvious. The contraction characteristics
of the two methods differ, and we, therefore, examined the triggering
sequence in field-stimulated cells. Isolated rat cardiomyocytes were
plated on laminin-coated coverslips that were mounted on an inverted
light microscope and superfused with HEPES-Tyrode buffer (pH 7.4;
37 degrees C). The cells were stimulated to contract either by a
0.5-ms current injection (CC cells) through high-resistance electrodes
or a 5-ms biphasic field-stimulation pulse (FS cells), and drugs
were added to block sarcolemmal proteins involved in excitation-contraction
coupling. Time to peak contraction (TTP) was significantly longer
in FS cells and was not affected by the polarity or the length
of the stimulus pulse. Tetrodotoxin (TTX; 20 microM) blocked cell
shortening in CC cells but not in FS cells. {N}i$^{2+}$ (5 mM) blocked
cell shortening in FS cells, whereas KB-R7943 (KB; 5 microM)
had no effect either on cell shortening or TTP. In FS cells,
nifedipine (Nif; 100 microM) and {C}d$^{2+}$ (300 microM) reduced
fractional
shortening by 34 and 63\%, respectively, but only {C}d$^{2+}$ affected
TTP (reduced by 48\%). A combination of Nif and KB reduced cell
shortening by 50\%, whereas a combination of {C}d$^{2+}$ and KB almost
abolished cell shortening. We conclude that field stimulation per
se prolongs TTP and that cell shortening in FS cells is not dependent
on {N}a$^{+}$ current but is triggered by a combination of L-type
{C}a$^{2+}$
current and reverse mode {N}a$^{+}$/{C}a$^{2+}$ exchange.},
added-at = {2009-06-03T11:20:58.000+0200},
author = {B�kenes, Janny and Sjaastad, Ivar and Sejersted, Ole M},
biburl = {https://www.bibsonomy.org/bibtex/23441903f42e1dcfd97390aa6e43eaf6b/hake},
description = {The whole bibliography file I use.},
doi = {10.1152/japplphysiol.00630.2004},
file = {Boke_2005_1712.pdf:Boke_2005_1712.pdf:PDF},
interhash = {64b551803da218173e38675c671db72b},
intrahash = {3441903f42e1dcfd97390aa6e43eaf6b},
journal = {J. Appl. Physiol.},
key = 15,
keywords = {15640393 5-HT4, AMP, Agents, Agonists, Animals, Antagonists, Cardiac, Cardiotonic Cell Chain Comparative Concentration, Congestive, Contraction, Cyclic Failure, Fibroblasts, Gov't, Heart Hematoporphyrins, Humans, Hydrogen-Ion Indoles, Infarction, Line, Male, Membrane Mesoporphyrins, Messenger, Muscles, Myocardial Myocytes, Non-U.S. Papillary Photosensitizing Polymerase Porphyrins, Potentials, RNA, Rats, Reaction, Receptors, Research Reverse Serotonin Serotonin, Skin, Study, Sulfonamides, Support, Tetraethylammonium, Transcriptase Tumor, Wistar,},
month = May,
number = 5,
pages = {1712-9},
pii = {00630.2004},
timestamp = {2009-06-03T11:21:07.000+0200},
title = {Artifactual contractions triggered by field stimulation of cardiomyocytes.},
url = {http://dx.doi.org/10.1152/japplphysiol.00630.2004},
volume = 98,
year = 2005
}