Protein tyrosine kinase-dependent modulation of isoflurane effects on cardiac sarcolemmal KATP 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 muM) 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 muM. Another PTK inhibitor, tyrphostin B42, had a similar effect. The inactive analog of genistein, daidzein (50 muM), did not elicit K-ATP current. Isoflurane (0.5 mm) increased genistein (35 muM)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 (I mm) prevented their actions on K-ATP current. In excised inside-out membrane patches, and at fixed 0.2 mm internal ATP, genistein (50 muM) 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 111 (1 mug/ml), isoflurane significantly increased open probability to 0.473 +/- 0.114. Conclusions: These results suggest that the PTK-protein tyrosine phosphatase signaling pathway may he 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.