Domain Potassium Channel Family Research Articles

TASK-1 regulates mitochondrial function under hypoxia

TASK-1, TWIK-related acid-sensitive potassium channel 1, is a member of the two-pore- domain potassium channel family. It is constitutively active at resting potentials and strongly expressed in the heart. However, little is known about the role of TASK-1 channels in hypoxia. A cellular model of hypoxia and reoxygenation from rat heart-derived H9c2 cells or TASK-1 deficient HEK293T cells was employed to explore the role of TASK-1 channels in cytoprotection against hypoxia. The cell viability assay revealed that TASK-1 expression increased the number of viable cells subjected to 2 h of hypoxia followed by 2 h of reoxygenation (H/R). To dissect the protective role of TASK-1 on mitochondrial function, mitochondrial membrane potential (MMP) was assessed by tetramethylrhodamine fluorescence. It was demonstrated that MMP was significantly decreased by H/R, but it was maintained by TASK-1 expression or pretreatment with cyclosporin A, an inhibitor of mitochondrial permeability transition pore (mPTP). The effect of cyclosporin A on MMP was not further altered by TASK-1 expression. Moreover, TASK-1 expression significantly blocked cytochrome c release induced by H/R. While a small fraction of endogenous TASK-1 was found to colocalize with the mitochondrial marker MitoTracker in H9c2 cells, H/R did not alter the extent of colocalization of TASK-1 with MitoTracker. The total TASK-1 protein level was not significantly affected by H/R. In summary, we provided the evidence that TASK-1 channels confer cytoprotection against hypoxia-reoxygenation injury, possibly by their capacity of maintaining the mitochondrial membrane potential via inhibiting MPTP opening.

Impact Of Hypoxia In The Expression And Regulation Of The TASK‐1 Potassium Channel In Cardiac Myocytes

TASK‐1 is a member of the two‐pore domain potassium channel family and strongly expressed in the heart. However, little is known about the roles and regulation of TASK‐1 channels in cardiac hypoxia. The present study was designed to investigate whether hypoxia modulated the expression and function of TASK‐1 and whether protein kinase C (PKC) was critical in hypoxia‐mediated processes in adult rat cardiac myocytes. The effects of acute hypoxia on the TASK‐1 channel function were chemically induced by sodium cyanide (NaCN). Activity of TASK‐1 in cardiomyocytes was investigated by the whole‐cell patch‐clamp technique. The current flowing through TASK‐1 channels in cardiac myocytes was quantified by analyzing the effects of extracellular pH or the selective TASK‐1 inhibitor methanandamide on the steady‐state current‐voltage relation. The voltage protocol, which included voltage ramps from +40 to −100 mV preceded by a test pulse from 0 to +40 mV, was designed to inactivate voltage‐dependent ion channels. In addition, a blocker cocktail, that had no effect on TASK‐1 channels expressed in HEK293T cells, was used to eliminate a number of ion channels in cardiac myocytes. Our data show that exposure of cardiac myocytes to NaCN for 5 minutes reduced the steady‐state outward current at +40 mV, an effect that was abolished by pretreatment with methanandamide. Either methanandamide or extracellular acidification (from pH 7.4 to 6.4) decreased the outward current, identifying TASK‐1 as the channel mediating this effect. Interestingly, the NaCN‐induced reduction in the outward current was largely prevented by pretreatment with the PKC selective inhibitor bisindolylmaleimide. To assess the expression and protective role of TASK‐1 in hypoxia, the prolonged hypoxia (4 hours) was employed by incubating cells in an airtight chamber in which O2 was replaced by N2 with glucose‐free Tyrode's solution. While 4 hours of hypoxia caused a significant reduction in the viability of cardiac myocytes, the inhibition of cardiac TASK‐1 channels by methanandamide further increased hypoxia‐induced cell death. Western blot analysis showed that 4 hours of hypoxia led to a decrease in the protein expression of TASK‐1 in cardiac myocytes. In summary, we provided the evidence that TASK‐1 channels in cardiomyocytes is regulated by hypoxia‐induced PKC signaling in cardiomyocytes. Our data are also supportive for a possible role of TASK‐1 channels in the cardioprotection against hypoxia.

Vascular Response in Mice Deficient in the Potassium Channel, TREK‐1

TREK‐1, a member of the two‐pore domain potassium channel family, is highly expressed in the vascular system. We hypothesize that TREK‐1 is involved with regulating the diameter of cerebral vessels. A TREK‐1 knockout mouse (KO) was generated by replacing the first two coding exons of TREK‐1 with a neomycin/beta‐galactosidase cassette. KO mice had normal blood pressure and cardiac function. Vascular responses were measured in isolated basilar arteries (BA) and middle cerebral arteries (MCA). Linoleic acid (LA, 10 μM and 100 μM), an activator of TREK‐1 and Ca‐activated K channels (BKCa), dilated pre‐constricted BA of wild‐type (WT) and KO mice to a similar extent. However, after selectively blocking BKCa with penitrem A, the dilation to LA in BA from KO mice was reduced 19±5% (n=6), while it was not affected in WT. This suggests that part of LA‐induced dilation is mediated via TREK‐1. Acetylcholine‐mediated dilations in BA and ATP‐mediated dilations in MCA of KO mice were not different from WT mice, either before or after inhibition of nitric oxide synthase. We conclude that TREK‐1 can regulate diameter of cerebral arteries; however, it does not appear to be involved with certain endothelial mediated dilations. This project is supported by a Predoctoral Fellowship 0815342F (KN) and grant 0665100Y (SPM) from American Heart Association, and NIH grants RO1 NS‐46666 (RMB), PO1 NS‐038660 (RMB), RO1 HL‐088435 (SPM).