ATP-sensitive Potassium Channel in Mitochondria of the Eukaryotic Microorganism Acanthamoeba castellanii

Abstract

We describe the existence of a potassium ion transport mechanism in the mitochondrial inner membrane of a lower eukaryotic organism, Acanthamoeba castellanii. We found that substances known to modulate potassium channel activity influenced the bioenergetics of A. castellanii mitochondria. In isolated mitochondria, the rate of resting respiration is increased by about 10% in response to potassium channel openers, i.e. diazoxide and BMS-191095, during succinate-, malate-, or NADH-sustained respiration. This effect is strictly dependent on the presence of potassium ions in an incubation medium and is reversed by glibenclamide (a potassium channel blocker). Diazoxide and BMS-191095 also caused a slight but statistically significant depolarization of mitochondrial membrane potential (measured with a TPP؉ -specific electrode), regardless of the respiratory substrate used. The resulting steady state value of membrane potential was restored after treatment with glibenclamide or 1 mM ATP. Additionally, the electrophysiological properties of potassium channels present in the A. castellanii inner mitochondrial membrane are described in the reconstituted system, using black lipid membranes. Conductance from 90 ؎ 7 to 166 ؎ 10 picosiemens, inhibition by 1 mM ATP/Mg 2؉ or glibenclamide, and activation by diazoxide were observed. These results suggest that an ATP-sensitive potassium channel similar to that of mammalian mitochondria is present in A. castellanii mitochondria.

Evidences for an ATP-sensitive potassium channel (KATP) in muscle and fat body mitochondria of insect

“…Thus, the observed effect is due to potassium ion transport mediated by potassium channels located in inner mitochondrial membrane. The discrete but statistically significant changes evoked by KCOs in the respiratory rate (the increase up to 13% for diazoxide and 20% for pinacidil) state in agreement with the previous study on mammalian (Garlid and Paucek, 2003) or amoeba mitochondria (Kicinska et al, 2007). Garlid and Paucek (2001) show that K ATP channels in mammalian mitochondria are low copy number proteins thereby their activity must be under strict control to avoid uncoupling.…”

“…The results are in agreement with studies on amoeba mitochondria (Kicinska et al, 2007) and in contrast to results obtained with plant isolated mitochondria (Matkovic et al, 2011;Pastore et al, 1999).…”

“…The weak inhibitory effect of 5-HD on mitoK ATP activity, like in mammals (Debska et al, 2002) was observed in insect mitochondria, but not in amoeba (Kicinska et al, 2007) or plant mitochondria (Matkovic et al, 2011;Pastore et al, 1999;Ruy et al, 2004). Jaburek et al (1998) argue that action of this drug may modify the channels conformation, when succinate is substrate.…”

“…Further studies have shown that channels with similar activity occur in the heart (Paucek et al, 1992), brain (Bajgar et al, 2001;Debska et al, 2001), kidney (Cancherini et al, 2003), skeletal muscle (Debska et al, 2002) and human T lymphocytes (Dahlem et al, 2004). Apart from human and animal mitochondria, the ATPsensitive potassium channel was also functionally characterized in plant mitochondria (Matkovic et al, 2011;Pastore et al, 1999), amoeba Acanthamoeba castellanii (Kicinska et al, 2007), nematode Caenorhabditis elegans (Wojtovich et al, 2008) and protozoan parasites trypanosomatids Trypanosoma cruzi (Costa and Krieger, 2009) Molecular identification of mitoK ATP is still not defined, however pharmacological profile and immunoreactivity suggest structural homology between mitoK ATP and K ATP in the plasma membrane. Some reports indicate that mitoK ATP are composed of four pore-forming Kir6.1 or/and Kir6.2 subunits belonging to the family of the inward-rectifier K + channel family Kir6.x (Foster et al, 2008;Lacza et al, 2003).…”

Physiology of potassium channels in the inner membrane of mitochondria

“…In the non-photosynthesising free-living amoeboid protist Acanthamoeba castellanii, the electrophysiological (singlechannel properties of the channel reconstituted into planar lipid membrane) and pharmacological (effect of specific modulators on bioenergetics of isolated mitochondria) profiles of the observed mitoK ATP channel display similarities to mammalian plasma membrane K ATP channel [103]. Swelling experiments have been used to assess the effects of some of the above-mentioned substances, known to modulate the mammalian mitoK ATP channel, on mitochondria of protozoan parasites trypanosomatids Trypanosoma cruzi (which causes Chagas' disease) and…”