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Relationship between transient outward K + current and Ca 2+ influx in rat cardiac myocytes of endo‐ and epicardial origin
Author(s) -
Volk Tilmann,
Nguyen Thi HongDiep,
Schultz JobstHendrik,
Ehmke Heimo
Publication year - 1999
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1111/j.1469-7793.1999.0841n.x
Subject(s) - myocyte , cardiac transient outward potassium current , depolarization , medicine , repolarization , patch clamp , biophysics , chemistry , electrophysiology , biology
1 The transient outward K + current ( I to ) is a major repolarizing ionic current in ventricular myocytes of several mammals. Recently it has been found that its magnitude depends on the origin of the myocyte and is regulated by a number of physiological and pathophysiological signals. 2 The relationship between the magnitude of I to , action potential duration (APD) and Ca 2+ influx ( Q Ca ) was studied in rat left ventricular myocytes of endo‐ and epicardial origin using whole‐cell recordings and the action potential voltage‐clamp method. 3 Under control conditions, in response to a depolarizing voltage step to +40 mV, I to averaged 12.1 ± 2.6 pA pF −1 in endocardial ( n = 11 ) and 24.0 ± 2.6 pA pF −1 in epicardial myocytes ( n = 12 ; P < 0.01 ). APD 90 (90 % repolarization) was twice as long in endocardial myocytes, whereas Q Ca inversely depended on the magnitude of I to . L‐type Ca 2+ current density was similar in myocytes from both regions. 4 To determine the effects of controlled reductions of I to on Q Ca , recordings were repeated in the presence of increasing concentrations of the I to inhibitor 4‐aminopyridine. 5 Inhibition of I to by as little as 20 % more than doubled Q Ca in epicardial myocytes, whereas it had only a minor effect on Q Ca in myocytes of endocardial origin. Further inhibition of I to led to a progressive increase in Q Ca in epicardial myocytes; at 90 % inhibition of I to , Q Ca was four times larger than the control value. 6 We conclude that moderate changes in the magnitude of I to strongly affect Q Ca primarily in epicardial regions. An alteration of I to might therefore allow for a regional regulation of contractility during physiological and pathophysiological adaptations.