Glucose-Stimulated Insulin Secretion Fundamentally Requires HO Signaling by NADPH Oxidase 4.

NADPH facilitates glucose-stimulated insulin secretion (GSIS) in pancreatic islets (PIs) of β-cells through an as yet unknown mechanism. We found NADPH oxidase isoform 4 (NOX4) to be the main producer of cytosolic HO, which is essential for GSIS; an increase in ATP alone was insufficient for GSIS. The fast GSIS phase was absent from PIs from NOX4-null, β-cell-specific knockout mice (NOX4βKO) (though not from NOX2 knockout mice) and from NOX4-silenced or catalase-overexpressing INS-1E cells.

Calpeptin, not calpain, directly inhibits an ion channel of the inner mitochondrial membrane.

The permeability transition pore (PTP) of inner mitochondrial membranes is a large conductance pathway for ions up to 1500 Da which opening is responsible for ion equilibration and loss of membrane potential in apoptosis and thus in several neurodegenerative diseases. The PTP can be regulated by the Ca(2+)-activated mitochondrial K channel (BK). Calpains are Ca(2+)-activated cystein proteases; calpeptin is an inhibitor of calpains.

Modulation of the mitochondrial large-conductance calcium-regulated potassium channel by polyunsaturated fatty acids.

Polyunsaturated fatty acids (PUFAs) and their metabolites can modulate several biochemical processes in the cell and thus prevent various diseases. PUFAs have a number of cellular targets, including membrane proteins. They can interact with plasma membrane and intracellular potassium channels.

Mitochondrial but not plasmalemmal BK channels are hypoxia-sensitive in human glioma.

Tumor cells are resistant to hypoxia but the underlying mechanism(s) of this tolerance remain poorly understood. In healthy brain cells, plasmalemmal Ca(2+)-activated K(+) channels ((plasma)BK) function as oxygen sensors and close under hypoxic conditions. Similarly, BK channels in the mitochondrial inner membrane ((mito)BK) are also hypoxia sensitive and regulate reactive oxygen species production and also permeability transition pore formation.

Interaction of the antibiotic minocycline with liver mitochondria - role of membrane permeabilization in the impairment of respiration.

Several studies have proposed that the antibiotic minocycline (MC) has cytoprotective activities. Nevertheless, when cells have been exposed to MC at micromolar concentrations, detrimental effects have been also observed. Despite the known inhibitory activity of MC on ATP synthesis and the Ca(2+) retention capacity of isolated rat liver and brain mitochondria, the underlying mechanism is still debated.

Putative Structural and Functional Coupling of the Mitochondrial BKCa Channel to the Respiratory Chain.

Potassium channels have been found in the inner mitochondrial membranes of various cells. These channels regulate the mitochondrial membrane potential, the matrix volume and respiration. The activation of these channels is cytoprotective.

What is the nature of the mitochondrial permeability transition pore and what is it not?

Since about 60 years a phenomenon now called permeability transition is known in mitochondria. It involves a large pore in the inner mitochondrial membrane, the permeability transition pore (PTP) whose molecular structure is still unknown. Year after year, new hypotheses have been developed how this pore could look like and which proteins cold be structural elements.

Complex effects of 17β-estradiol on mitochondrial function.

Existing literature on estradiol indicates that it affects mitochondrial functions at low micromolar concentrations. Particularly blockade of the permeability transition pore (PTP) or modulation of the enzymatic activity of one or more complexes of the respiratory chain were suspicious. We prepared mitoplasts from rat liver mitochondria (RLM) to study by single-channel patch-clamp techniques the PTP, and from rat astrocytes to study the potassium BK-channel said to modulate the PTP.

Activation of the permeability transition pore by Bax via inhibition of the mitochondrial BK channel.

Mitochondria are crucially involved in the intrinsic pathway of apoptosis. Upon induction of apoptosis, proapoptotic proteins of the Bcl-2 family, in particular Bax and Bak, transfer the death signal to the organelle. The outcome is release of proapoptotic factors, such as cytochrome c, and mitochondrial changes, such as depolarization.

The dopamine-D2-receptor agonist ropinirole dose-dependently blocks the Ca2+-triggered permeability transition of mitochondria.

Ropinirole, an agonist of the post-synaptic dopamine D2-receptor, exerts neuroprotective activity. The mechanism is still under discussion. Assuming that this neuroprotection might be associated with inhibition of the apoptotic cascade underlying cell death, we examined a possible effect of ropinirole on the permeability transition pore (mtPTP) in the mitochondrial inner membrane.

Interaction of mitochondrial potassium channels with the permeability transition pore.

Three types of potassium channels cooperate with the permeability transition pore (PTP) in the inner mitochondrial membranes of various tissues, mtK((ATP)), mtBK, and mtKv1.3. While the latter two share similarities with their plasma membrane counterparts, mtK((ATP)) exhibits considerable differences with the plasma membrane K((ATP))-channel.

Direct inhibition of the mitochondrial permeability transition pore: a possible mechanism for better neuroprotective effects of allopregnanolone over progesterone.

We previously demonstrated that the progesterone (PROG) metabolite allopregnanolone (AP) is more potent than PROG in the treatment of traumatic brain injury (TBI) and stroke, but the mechanisms for this differential effect are little understood. The mitochondrial permeability transition pore (mtPTP) appears to be a key player in the intrinsic pathway of apoptosis-induced loss of neurons. Its activation is accompanied by the release of cytochrome c (cyt c) from the intermembrane gap and subsequent cell death.

Impairment of mitochondrial function by minocycline.

There is an ongoing debate on the presence of beneficial effects of minocycline (MC), a tetracycline-like antibiotic, on the preservation of mitochondrial functions under conditions promoting mitochondria-mediated apoptosis. Here, we present a multiparameter study on the effects of MC on isolated rat liver mitochondria (RLM) suspended either in a KCl-based or in a sucrose-based medium. We found that the incubation medium used strongly affects the response of RLM to MC.

Inhibitory modulation of the mitochondrial permeability transition by minocycline.

The semi-synthetic tetracycline derivative minocycline exerts neuroprotective properties in various animal models of neurodegenerative disorders. Although anti-inflammatory and anti-apoptotic effects are reported to contribute to the neuroprotective action, the exact molecular mechanisms underlying the beneficial properties of minocycline remain to be clarified. We analyzed the effects of minocycline in a cell culture model of neuronal damage and in single-channel measurements on isolated mitoplasts.

Hypoxia increases activity of the BK-channel in the inner mitochondrial membrane and reduces activity of the permeability transition pore.

Hypoxia can cause severe damage to cells by initiating signaling cascades that lead to cell death. A cellular oxygen sensor, other than the respiratory chain, might exist in sensitive components of these signaling cascades. Recently, we found evidence that mitochondrial ion channels are sensitive to low levels of oxygen.

Nephrotoxicity and its prevention by taurine in tamoxifen induced oxidative stress in mice.

Tamoxifen (TAM) is an anti-neoplastic drug used for the treatment of breast cancer. It decreases the hexose monophosphate shunt and thereby increasing the incidence of oxidative stress in cells leading to tissue injury. The present study was undertaken to investigate modulatory effects of taurine on the nephrotoxicity of TAM with special reference to protection against disruption of nonenzymatic and enzymatic antioxidants.

Hypoxia increases BK channel activity in the inner mitochondrial membrane.

To explore the potential function of the BK channel in the inner mitochondrial membrane under physiological and hypoxic conditions, we used on-mitoplast and whole-mitoplast patches. Single BK channels had a conductance of 276+/-9 pS under symmetrical K(+) solutions, were Ca(2+)- and voltage-dependent and were inhibited by 0.1 microM charybdotoxin.

Combined modulation of the mitochondrial ATP-dependent potassium channel and the permeability transition pore causes prolongation of the biphasic calcium dynamics.

The permeability transition pore (PTP) and the ATP-dependent potassium (mtK-ATP) channel of mitochondria are known to play key roles in mitochondrially mediated apoptosis. We investigated how modulation of the permeability transition pore (PTP) and the ATP-dependent potassium (mtK-ATP) channel, either as single elements or in combination, affects the proapoptotic intracellular calcium ([Ca(2+)](i)) transients and the mitochondrial membrane potential (psi(m)). For this purpose a model was established exploring the [Ca(2+)](i) transients in N2A cells using continuous application of ATP that causes a biphasic [Ca(2+)](i) response.

Patch clamp reveals powerful blockade of the mitochondrial permeability transition pore by the D2-receptor agonist pramipexole.

The dopamine-D2-agonist pramipexole (PPX) was tested for blocking mitochondrial permeability transition (PT) in order to give a possible explanation for its neuroprotective effect seen in PPX-treated Parkinson's disease patients. Patch-clamp techniques for studying single-channel currents in the inner mitochondrial membrane and large-amplitude swelling of energized mitochondria were used to study PPX action on the permeability transition pore (PTP), a key player in the mitochondrial route of the apoptotic cascade. Identity of the PTP was proven by measuring the concentration-response relation for cyclosporin A-blockade (IC50=26 nM).

The neurotrophin receptor TrkB is colocalized to mitochondrial membranes.

The transmembrane tyrosine-specific protein kinase TrkB has been shown to serve as a receptor for the neurotrophic factors BDNF and NT-4. Neurotrophin binding to TrkB isoformes mediates many intracellular signaling pathways, including calcium signalling. Two truncated isoforms of the receptor, lacking the tyrosine kinase activity, signal through a yet unknown pathway.

Fatty acids induce chloride permeation in rat liver mitochondria by activation of the inner membrane anion channel (IMAC).

The inner membrane of freshly isolated mammalian mitochondria is poorly permeable to Cl(-). Low, nonlytic concentrations (< or =30 microM) of long-chain fatty acids or their branched-chain derivatives increase permeation of Cl(-) as indicated from rapid large-scale swelling of mitochondria suspended in slightly alkaline KCl medium (supplemented with valinomycin). Myristic, palmitic, or 5-doxylstearic acid are powerful inducers of Cl(-) permeation, whereas lauric, phytanic, stearic, or 16-doxylstearic acid stimulate Cl(-) permeation in a lesser extent.

The human mitochondrial KATP channel is modulated by calcium and nitric oxide: a patch-clamp approach.

ATP-sensitive potassium channels of the inner mitochondrial membrane (mtKATP) are blocked by ATP. They are suggested to be involved in protective mechanisms such as ischemic preconditioning (IPC). Here we identify this channel type for the first time in a human cell line (Jurkat cells).

Direct inhibition of the mitochondrial permeability transition pore: a possible mechanism responsible for anti-apoptotic effects of melatonin.

Melatonin, the secretory product of the pineal gland, is known to be neuroprotective in cerebral ischemia, which is so far mostly attributed to its antioxidant properties. Here we show that melatonin directly inhibits the mitochondrial permeability transition pore (mtPTP). mtPTP contributes to the pathology of ischemia by releasing calcium and cytochrome c (cyt c) from mitochondria.

Single-channel currents of the permeability transition pore from the inner mitochondrial membrane of rat liver and of a human hepatoma cell line.

Single-channel currents were recorded from inner mitochondrial membranes of HepG2 hepatoma cells and of normal rat liver cells by means of patch-clamp techniques. The current events showed variable amplitudes of up to 1.1 +/- 0.

Methyl pyruvate stimulates pancreatic beta-cells by a direct effect on KATP channels, and not as a mitochondrial substrate.

In pancreatic beta-cells, methyl pyruvate is a potent secretagogue and is widely used to study stimulus-secretion coupling. In contrast with pyruvate, which barely stimulates insulin secretion, methyl pyruvate was suggested to act as an effective mitochondrial substrate. We show that methyl pyruvate elicited electrical activity in the presence of 0.