Regulation of Kv4 channel expression in failing rat heart by the thioredoxin system

Abstract

Redox imbalance elicited by oxidative stress contributes to pathogenic remodeling of ion channels that underlies arrhythmogenesis and contractile dysfunction in the failing heart. This study examined whether the expression of K(+) channels in the remodeled ventricle is controlled by the thioredoxin system, a principal oxidoreductase network regulating redox-sensitive proteins. Ventricular dysfunction was induced in rats by coronary artery ligation, and experiments were conducted 6-8 wk postinfarction. Biochemical assays of tissue extracts from infarcted hearts showed that thioredoxin reductase activity was decreased by 32% from sham-operated controls (P < 0.05), whereas thioredoxin activity was 51% higher postinfarction (P < 0.05). These differences in activities paralleled changes in protein abundance as determined by Western blot analysis. However, whereas real-time PCR showed thioredoxin reductase mRNA levels to be significantly decreased postinfarction, thioredoxin mRNA was not altered. In voltage-clamp studies of myocytes from infarcted hearts, the characteristic downregulation of transient-outward K(+) current density was reversed by exogenous pyruvate (5 mmol/l), and this effect was blocked by the specific inhibitors of the thioredoxin system: auranofin or 13-cis-retinoic acid. Real-time PCR and Western blot analyses of myocyte suspensions from infarcted hearts showed that pyruvate increased mRNA and protein abundance of Kv4.2 and Kv4.3 channel alpha-subunits as well as the accessory protein KChIP2 when compared with time-matched, untreated cells (P < 0.05). The pyruvate-induced increase in Kv4.x expression was blocked by auranofin, but the upregulation of KChIP2 expression was not affected. These data suggest that the expression of Kv4.x channels is redox-regulated by the thioredoxin system, which may be a novel therapeutic target to reverse or limit electrical remodeling of the failing heart.

Role of Apoptosis Signal-Regulating Kinase-1-c-Jun NH2-Terminal Kinase-p38 Signaling in Voltage-Gated K+Channel Remodeling of the Failing Heart: Regulation by Thioredoxin

“…As shown in Figure 3A, 10 nM IGF-1 for 4-5 h upregulated I to density in myocytes from MI hearts (filled squares) to a similar extent as JNK=p38 inhibitors. Moreover, in a separate series of experiments this effect was blocked by the TrxR inhibitor AF (10 nM; filled diamonds), implicating the involvement of the Trx system in the regulation of Kv channels (22). In contrast to the response of post-MI myocytes, IGF-1 had no effect on I to in myocytes from sham rats (Fig.…”

“…A chronic MI model of ventricular dysfunction was used in the present investigation as described previously (22,33,42). Briefly, male Sprague-Dawley rats (180-200 g) were intubated and artificially ventilated under Brevital (methohexital Ò sodium) anesthesia at 50 mg=kg, i.p.…”

“…In addition, there is compensatory hypertrophy of the surviving myocardium as reflected by a marked increase in heart weight-to-body weight ratio (33,42). At the cellular level, this model is characterized by marked alterations in redox balance, particularly increased superoxide production, reduced glutathione (GSH) depletion, and significant decreases in the activities of g-glutamylcysteine synthetase, glutathione reductase, and TrxR1, compared with sham-operated control rats (22,33). Thus, the chronic dysfunction of the left ventricle elicited by MI is paralleled by markers of oxidative stress and resulting shift in cell redox state.…”

“…and the hearts were excised and perfused via the coronary vasculature by the Langendorff method. In some experiments, myocytes were dissociated from perfused hearts by a collagenase digestion procedure described previously (20,22,33). Dispersed myocytes from surviving regions of the left ventricle and septum were suspended in Dulbecco's modified Eagle's medium/Ham's F12 (DMEM/F12) and stored in an incubator at 378C until used, usually within 6 h of isolation.…”

“…Although the electrophysiology of the remodeled ventricle involves changes in several types of ion channels, downregulation of voltagegated K þ (Kv) channels underlying the transient outward K þ current (I to ) is perhaps the most consistent change observed in heart failure, both in the human heart (2,14) and in animal models (2,15,20,22,33). In rodent hearts, a disease-related decrease in Kv channel expression participates in prolongation of the ventricular muscle action potential and alterations in refractory period (15).…”