A novel potassium channel in skeletal muscle mitochondria

Abstract

In this work we provide evidence for the potential presence of a potassium channel in skeletal muscle mitochondria. In isolated rat skeletal muscle mitochondria, Ca(2+) was able to depolarize the mitochondrial inner membrane and stimulate respiration in a strictly potassium-dependent manner. These potassium-specific effects of Ca(2+) were completely abolished by 200 nM charybdotoxin or 50 nM iberiotoxin, which are well-known inhibitors of large conductance, calcium-activated potassium channels (BK(Ca) channel). Furthermore, NS1619, a BK(Ca)-channel opener, mimicked the potassium-specific effects of calcium on respiration and mitochondrial membrane potential. In agreement with these functional data, light and electron microscopy, planar lipid bilayer reconstruction and immunological studies identified the BK(Ca) channel to be preferentially located in the inner mitochondrial membrane of rat skeletal muscle fibers. We propose that activation of mitochondrial K(+) transport by opening of the BK(Ca) channel may be important for myoprotection since the channel opener NS1619 protected the myoblast cell line C2C12 against oxidative injury.

Large-conductance Ca2+-activated potassium channel in mitochondria of endothelial EA.hy926 cells

“…The electrophysiological properties of this channel were studied in the inner mitochondrial membrane of the human endothelial cell line EA.hy926 using the patch-clamp technique in the mitoplast-attached mode. Large conductance (270 Ϯ 10 pS), voltage dependence, a higher open-state probability at positive potentials, sensitivity to Ca 2ϩ , and NS1619 (a BK Ca channel opener) and paxilline and iberiotoxin (BK Ca channel inhibitors) indicate the similarity of this channel to the mammalian mitoBK Ca channels previously reported in glioma (31), skeletal muscle (33), brain (14,33), and cardiac (40) cells. Interestingly, a mitoBK Ca channel with similar electrophysiological properties (although with a much higher conductance of 502-605 pS) has been recently described in nonmammalian mitochondria (potato tuber) mitochondria (22).…”

“…These studies provide concrete morphological evidence for the existence mitoBK Ca channels (␣-subunit) in the inner mitochondrial membrane of rat brain cells. Moreover, rat skeletal muscle and brain mitochondria show immunoreactivity against antibodies targeting the BK Ca ␤ 4 -subunit (27,32,33). These findings indicate a close molecular similarity between the mitoBK Ca channel and the plasma membrane BK Ca channel, suggesting that both channels are splice variants of the same gene product.…”

“…When compared with the full inhibitory effect of iberiotoxin on Ca 2ϩ -induced respiration and ⌬⌿ depolarization, this could indicate a nonspecific uncoupling effect of NS1619 and NS11021 within the concentration range of 20 to 50 M and 1 to 2.5 M, respectively, on isolated endothelial mitochondria (when 0.7 mg of mitochondrial protein is used) rather than the low sensitivity of the channel to iberiotoxin. Similarly, in some isolated mammalian mitochondria, the sensitivity of NS1619-or NS11021-induced respiration and ⌬⌿ depolarization to the mitoBK Ca channel blockers (iberiotoxin, charybdotoxin, and paxilline) is not complete (2,20,32,33). Moreover, in mitochondria isolated from EA.hy962 cells, concentrations of NS1619 above 50 M and NS11021 above 2.5 M caused a decrease in respiration and a further decrease in ⌬⌿, indicating an impairment of the respiratory chain by higher concentrations of the potassium channel openers.…”

Brain mitochondrial ATP-insensitive large conductance Ca+2-activated K+ channel properties are altered in a rat model of amyloid-β neurotoxicity

“…MitoBK Ca was also found in skeletal muscle (Skalska et al, 2008) and brain (Skalska et al, 2009;Douglas et al, 2006;Fahanik-Babaei et al, 2011a,b). A BK Ca channel is composed of four similar α-subunits that co-assemble around a central axis to form a single K + -selective conduction pore, plus β auxiliary subunits that co-associated with each α-subunits in a 1:1 ratio To date, four β subunits (β1-4) have been described with β1 being the principal form found in vascular smooth muscle cells, while β2 (chromaffin cells, brain, lung), β3 (testis, pancreas, spleen) and β4 (neuronal, lung) are thought to be restricted to other tissues (Orio et al, 2002;Salkoff et al, 2006;Wang et al, 2006).…”

Physiology of potassium channels in the inner membrane of mitochondria

“…MitoBK Ca (KCa1.1) (reviews [136-138, 181, 200]), displaying a conductance of 100-300 pS, has been observed by direct patch clamping of mitoplasts of mammalian cells [170,196] as well as in planar lipid bilayer experiments [173]. The channel has been identified Fig.…”