Protein tyrosine kinase-dependent modulation of isoflurane effects on cardiac sarcolemmal K(ATP) channel.
BACKGROUND
Cardiac adenosine triphosphate-sensitive potassium (K(ATP)) channels and protein tyrosine kinases (PTKs) are mediators of ischemic preconditioning, but the interaction of both and a role in myocardial protection afforded by volatile anesthetics have not been defined.


METHODS
Whole cell and single channel patch clamp techniques were used to investigate the effects of isoflurane and the PTK inhibitor genistein on the cardiac sarcolemmal K(ATP) channel in acutely dissociated guinea pig ventricular myocytes.


RESULTS
At 0.5 mm internal ATP, genistein (50 microm) elicited whole cell K(ATP) current (22.5 +/- 7.9 pA/pF). Genistein effects were concentration-dependent, with an EC50 of 32.3 +/- 1.4 microm. Another PTK inhibitor, tyrphostin B42, had a similar effect. The inactive analog of genistein, daidzein (50 microm), did not elicit K(ATP) current. Isoflurane (0.5 mm) increased genistein (35 microm)-activated whole cell K(ATP) current from 14.5 +/- 3.1 to 32.5 +/- 6.6 pA/pF. Stimulation of receptor PTKs with epidermal growth factor, nerve growth factor, or insulin attenuated genistein and isoflurane effects, and the protein tyrosine phosphatase inhibitor orthovanadate (1 mm) prevented their actions on K(ATP) current. In excised inside-out membrane patches, and at fixed 0.2 mm internal ATP, genistein (50 microm) increased channel open probability from 0.053 +/- 0.016 to 0.183 +/- 0.039, but isoflurane failed to further increase open probability (0.162 +/- 0.051) of genistein-activated channels. However, applied in the presence of genistein and protein tyrosine phosphatase 1B (1 microg/ml), isoflurane significantly increased open probability to 0.473 +/- 0.114.


CONCLUSIONS
These results suggest that the PTK-protein tyrosine phosphatase signaling pathway may be one of the regulators of cardiac sarcolemmal K(ATP) channel and may play a role in modulating its responsiveness to isoflurane. Relative importance of this modulation for cardioprotection by volatile anesthetics remains to be established.
Stadnicka
Anna
A
Department of Anesthesiology, Medical College of Wisconsin, Milwaukee 53226, USA. astadnic@mcw.edu
Kwok
Wai-Meng
WM
Warltier
David C
DC
Bosnjak
Zeljko J
ZJ
D000255:Adenosine Triphosphate / Q000494:pharmacology*; D018685:Anesthetics, Inhalation / Q000494:pharmacology*; D000818:Animals; D004357:Drug Synergism; D005260:Female; D019833:Genistein / Q000494:pharmacology; D006168:Guinea Pigs; D006321:Heart / Q000187:drug effects*; D007530:Isoflurane / Q000494:pharmacology*; D008297:Male; D015221:Potassium Channels / Q000187:drug effects*; D011505:Protein-Tyrosine Kinases / Q000502:physiology*; D012508:Sarcolemma / Q000187:drug effects
D018685:Anesthetics, Inhalation; D015221:Potassium Channels; D000255:Adenosine Triphosphate; D007530:Isoflurane; D019833:Genistein; D011505:Protein-Tyrosine Kinases