%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 }