Regulation of transient outward current in human atrial myocytes by protein tyrosine kinase pathway.
BACKGROUND
Regulation of transient outward current (I(to)) in human myocytes is unclear. The present study investigated the effect of protein tyrosine kinase (PTK) inhibitors on I(to) in human atrial myocytes.


RESULTS
Atrial myocytes were isolated enzymatically from biopsies of human right atrial appendage obtained from patients undergoing coronary artery bypass surgery. I(to) was recorded by the whole-cell patch-clamp technique in voltage-clamp configuration. Two groups of PTK inhibitors, the ATP binding site PTK inhibitors genistein and AG957 and the protein substrate PTK inhibitors ST638 and PP2, significantly inhibited I(to) in a concentration-dependent manner, with a potency order of genistein>AG957>ST638>PP2. At test pulse potential of +60 mV, I(to) was inhibited by 28% +/- 3%, 59% +/- 3%, and 89% +/- 3% by 15, 50, and 100 microM genistein, respectively. Daidzein and PP3, inactive analogues of genistein and PP2, respectively, did not produce any inhibitory effects on I(to). In addition to the inhibition of I(to) amplitude, the protein substrate PTK inhibitors ST638 and PP2 significantly accelerated I(to) inactivation (current decay) and delayed recovery from inactivation. Inhibition of protein tyrosine phosphatase partially reversed the effect of genistein. Stimulation or inhibition of serine/ threonine kinases (PKA, PKC, and PKG) did not change I(to) or alter the inhibitory response of PTK inhibitors on I(to).


CONCLUSIONS
In human atrial cells, the PTK pathway plays an important role in the regulation of basal I(to), independent of serine/threonine kinases.
Wang
Yanggan
Y
The Sibley Heart Center, Department of Pediatrics, Emory University, Atlanta, Georgia 30322, USA.
Kumar
Rajiv
R
Wagner
Mary B
MB
Cheng
Jun
J
Mishra
Manjari
M
Joyner
Ronald W
RW
D000368:Aged; D001667:Binding, Competitive / Q000187:drug effects; D002450:Cell Communication / Q000187:drug effects / Q000502:physiology; D002934:Cinnamates / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004341:Drug Evaluation; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005260:Female; D019833:Genistein / Q000494:pharmacology; D006325:Heart Atria / Q000166:cytology*; D006801:Humans; D007473:Ion Channels / Q000187:drug effects*; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D008875:Middle Aged; D032383:Myocytes, Cardiac / Q000187:drug effects* / Q000502:physiology*; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors*; D013440:Sulfides / Q000494:pharmacology; D013997:Time Factors; D020032:Tyrphostins / Q000494:pharmacology
D002934:Cinnamates; D004791:Enzyme Inhibitors; D007473:Ion Channels; D013440:Sulfides; D020032:Tyrphostins; C104965:tyrphostin AG957; C060747:ST 638; D019833:Genistein; D011505:Protein-Tyrosine Kinases