VOLATILE ANESTHETIC ACTION ON CARDIAC K CHANNELS

描述（由申请人提供）：

DESCRIPTION (provided by applicant): Volatile anesthetics (VAs) have been in use for over a century, but their potent cardioprotective effects have only recently been established. However, the molecular mechanisms of anesthetic action on cardiac ion channels are unknown. A likely target for the antiarrhythmogenic action of the VAs is the slow delayed-rectifier potassium (IKs) channel that underlies a major repolarizing current in the mammalian heart. Inhibition of the IKs channel by the VAs will result in the prolongation of the action potential, similar in action to the Class III antiarrhythmic agents. The overall goal of this proposal is to elucidate a molecular model for the mechanism of VA action on the IKs channel. The proposed experiments will investigate the effects of VAs on the two-subunit components underlying IKs: a pore-forming region encoded by the gene KCNQ1 and an auxiliary regulatory p-subunit, minK. Preliminary results show that isoflurane exerts differential effects on KCNQ1 alone and in combination with the minK subunit. A novel mode of volatile anesthetic interaction with a channel protein where an auxiliary regulatory subunit modulates anesthetic action is postulated. The overall hypothesis is that the minK subunit diminishes the effect of VA on IKs. The patch clamp technique will be used to monitor functional changes in KCNQ1 and minK transiently expressed in a mammalian cardiac cell line. Changes in IKs function in native myocytes overexpressing minK will also be monitored. In addition, the Langendorff isolated guinea pig heart model will be used to determine the role of IKs in anesthetic-induced cardioprotection. The hypotheses to be tested are: 1. The minK subunit hinders the accessibility of an isoflurane interaction site on KCNQ1. 2. Phosphorylation of IKs by protein kinase A counteracts the inhibitory effects of isoflurane. 3. The differential anesthetic effects on the subunits are not unique to the KCNQl+mmK channel complex. 4. The KCNQ1 and minK subunits are differentially expressed in isoflurane-induced cardioprotection. In summary, this proposal will characterize the role of an auxiliary regulatory subunit, minK, on volatile anesthetic action on IKs. This novel approach to anesthetic interaction with ion channels will have functional significance in the diseased myocardium where up- and downregulation of channel subunits are known to occur.