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1.
Wojtovich AP Burwell LS Sherman TA Nehrke KW Brookes PS 《Biochemical and biophysical research communications》2008,376(3):625-628
Ischemic preconditioning (IPC) is an evolutionarily conserved endogenous mechanism whereby short periods of non-lethal exposure to hypoxia alleviate damage caused by subsequent ischemia reperfusion (IR). Pharmacologic targeting has suggested that the mitochondrial ATP-sensitive potassium channel (mKATP) is central to IPC signaling, despite its lack of molecular identity. Here, we report that isolated Caenorhabditis elegans mitochondria have a KATP channel with the same physiologic and pharmacologic characteristics as the vertebrate channel. Since C. elegans also exhibit IPC, our observations provide a framework to study the role of mKATP in IR injury in a genetic model organism. 相似文献
2.
Queliconi BB Wojtovich AP Nadtochiy SM Kowaltowski AJ Brookes PS 《Biochimica et biophysica acta》2011,1813(7):1309-1315
The mitochondrial ATP-sensitive potassium channel (mK(ATP)) is important in the protective mechanism of ischemic preconditioning (IPC). The channel is reportedly sensitive to reactive oxygen and nitrogen species, and the aim of this study was to compare such species in parallel, to build a more comprehensive picture of mK(ATP) regulation. mK(ATP) activity was measured by both osmotic swelling and Tl(+) flux assays, in isolated rat heart mitochondria. An isolated adult rat cardiomyocyte model of ischemia-reperfusion (IR) injury was also used to determine the role of mK(ATP) in cardioprotection by nitroxyl. Key findings were as follows: (i) mK(ATP) was activated by O(2)(-) and H(2)O(2) but not other peroxides. (ii) mK(ATP) was inhibited by NADPH. (iii) mK(ATP) was activated by S-nitrosothiols, nitroxyl, and nitrolinoleate. The latter two species also inhibited mitochondrial complex II. (iv) Nitroxyl protected cardiomyocytes against IR injury in an mK(ATP)-dependent manner. Overall, these results suggest that the mK(ATP) channel is activated by specific reactive oxygen and nitrogen species, and inhibited by NADPH. The redox modulation of mK(ATP) may be an underlying mechanism for its regulation in the context of IPC. This article is part of a Special Issue entitled: Mitochondria and Cardioprotection. 相似文献
3.
Ischemic preconditioning (IPC) has been considered to be a potential therapy to reduce ischemia-reperfusion injury (IRI) since the 1980s. Our previous study indicated that sevoflurane preconditioning (SPC) also reduced intestinal IRI in rats. However, whether the protective effect of SPC is similar to IPC and the mechanisms of SPC are unclear. Thus, we compared the efficacy of SPC and IPC against intestinal IRI and the role of protein kinase C (PKC) and mitochondrial ATP-sensitive potassium channel (mKATP) in SPC. A rat model of intestinal IRI was used in this study. The superior mesenteric artery (SMA) was clamped for 60 min followed by 120 min of reperfusion. Rats with IPC underwent three cycles of SMA occlusion for 5 min and reperfusion for 5 min before intestinal ischemia. Rats with SPC inhaled sevoflurane at 0.5 minimum alveolar concentration (MAC) for 30 min before the intestinal ischemic insult. Additionally, the PKC inhibitor Chelerythrine (CHE) or mKATP inhibitor 5-Hydroxydecanoic (5-HD) was injected intraperitoneally before sevoflurane inhalation. Both SPC and IPC ameliorated intestinal IRI-induced histopathological changes, decreased Chiu’s scores, reduced terminal deoxyribonucleotide transferase-mediated dUTP nick end labeling (TUNEL) positive cells in the epithelium, and inhibited the expression of malondialdehyde (MDA) and tumor necrosis factor-α (TNF-α). These protective effects of SPC were similar to those of IPC. Pretreatment with PKC or mKATP inhibitor abolished SPC—induced protective effects by increasing Chiu’s scores, down-regulated the expression of Bcl-2 and activated caspase-3. Our results suggest that pretreatment with 0.5 MAC sevoflurane is as effective as IPC against intestinal IRI. The activation of PKC and mKATP may be involved in the protective mechanisms of SPC. 相似文献
4.
Minners J Lacerda L Yellon DM Opie LH McLeod CJ Sack MN 《Molecular and cellular biochemistry》2007,294(1-2):11-18
The ischemic preconditioning biological phenomenon has been explored to identify putative pharmacologic agents to mimic this
cytoprotective program against cellular ischemic injury. Diazoxide administration confers this cytoprotection, however, whether
this is via direct activation of the putative mitochondrial KATP (mKATP) channel which was originally proposed has been questioned. Here, we present data supporting an alternate hypothesis evoking
mitochondrial respiratory inhibition rather than mKATP channel activation, as a mediating event in the diazoxide-activated cytoprotective program. Mitochondrial respiration and
reactive oxygen species (ROS) production was measured in digitonin-permeabilized C2C12 myotubes, allowing for the modulation
of mKATP conductance by changing the potassium concentration of the medium (0–130 mM). Diazoxide dose-dependently attenuated succinate-supported
respiration, an effect that was independent of mKATP channel conductance. Similarly, 5-hydroxydecanoate (5-HD), a putative mKATP channel blocker, released diazoxide-induced respiratory inhibition independently of potassium concentration. Since diazoxide-induced
cytoprotection and respiratory inhibition are both integrally linked to ROS generation we repeated above experiments following
ROS generation using DCF fluorescence. Cytoprotective doses of diazoxide increased ROS generation independently of potassium
concentration and 5-HD inhibited ROS production under the same conditions. Collectively these data support the hypothesis
that diazoxide-mediated cytoprotection is independent of the conductance of the mKATP channel and rather implicate mitochondrial respiratory inhibition-triggered ROS signaling. 相似文献
5.
Modulation of a plant mitochondrial K+ATP channel and its involvement in cytochrome c release 总被引:1,自引:0,他引:1
Chiandussi E Petrussa E Macrì F Vianello A 《Journal of bioenergetics and biomembranes》2002,34(3):177-184
Pea stem mitochondria, resuspended in a KCl medium (de-energized mitochondria), underwent a swelling, as a consequence of K+ entry, that was inhibited by ATP. This inhibition was partially restored by GTP and diazoxide (K+
ATP channel openers). In addition, glyburide and 5-hydroxydecanate (K+
ATP channel blockers) induced an inhibition of the GTP-stimulated swelling. Mitochondrial swelling was inhibited by H2O2, but stimulated by NO. The same type of responses was also obtained in succinate-energized mitochondria. When the succinate-dependent transmembrane electrical potential () had reached a steady state, the addition of KCl induced a dissipation that was inhibited by H2O2 and stimulated by NO. The latter stimulation was prevented by carboxy-PTIO, a NO scavenger. Phenylarsine oxide (a thiol oxidant) and NEM (a thiol blocker) stimulated the KCl-induced dissipation of , while DTE prevented this effect in both cases. In addition, DTE transiently inhibited the NO-induced dissipation of , but then it caused a more rapid collapse. These results, therefore, show that the plant mitochondrial K+
ATP channel resembles that present in mammalian mitochondria and that it appears to be modulated by dithiol–disulfide interconversion, NO and H2O2. The aperture of this channel was linked to the partial rupture of the outer membrane. The latter effect led to a release of cytochrome c, thus suggesting that this release may be involved in the manifestation of programmed cell death. 相似文献
6.
Daisuke Sunaga Masaya Tanno Atsushi Kuno Satoko Ishikawa Makoto Ogasawara Toshiyuki Yano Takayuki Miki Tetsuji Miura 《PloS one》2014,9(11)
Loss of mitochondrial membrane potential (ΔΨm) is known to be closely linked to cell death by various insults. However, whether acceleration of the ΔΨm recovery process prevents cell necrosis remains unclear. Here we examined the hypothesis that facilitated recovery of ΔΨm contributes to cytoprotection afforded by activation of the mitochondrial ATP-sensitive K+ (mKATP) channel or inactivation of glycogen synthase kinase-3β (GSK-3β). ΔΨm of H9c2 cells was determined by tetramethylrhodamine ethyl ester (TMRE) before or after 1-h exposure to antimycin A (AA), an inducer of reactive oxygen species (ROS) production at complex III. Opening of the mitochondrial permeability transition pore (mPTP) was determined by mitochondrial loading of calcein. AA reduced ΔΨm to 15±1% of the baseline and induced calcein leak from mitochondria. ΔΨm was recovered to 51±3% of the baseline and calcein-loadable mitochondria was 6±1% of the control at 1 h after washout of AA. mKATP channel openers improved the ΔΨm recovery and mitochondrial calcein to 73±2% and 30±7%, respectively, without change in ΔΨm during AA treatment. Activation of the mKATP channel induced inhibitory phosphorylation of GSK-3β and suppressed ROS production, LDH release and apoptosis after AA washout. Knockdown of GSK-3β and pharmacological inhibition of GSK-3β mimicked the effects of mKATP channel activation. ROS scavengers administered at the time of AA removal also improved recovery of ΔΨm. These results indicate that inactivation of GSK-3β directly or indirectly by mKATP channel activation facilitates recovery of ΔΨm by suppressing ROS production and mPTP opening, leading to cytoprotection from oxidant stress-induced cell death. 相似文献
7.
Binding of ouabain to Na+/K+-ATPase activated multiple signal transduction pathways including stimulation of Src, Ras, p42/44 MAPKs and production of reactive oxygen species (ROS) in rat cardiac myocytes. Inhibition of either Src or Ras ablated ouabain-induced increase in both [Ca2+]i and contractility. While PD98059 abolished the effects of ouabain on [Ca2+]i, it only caused a partial inhibition of ouabain-induced increases in contractility. On the other hand, pre-incubation of myocytes with N-acetyl cysteine (NAC) reduced the effects of ouabain on contractility, but not [Ca2+]i. Furthermore, 5-hydroxydecanoate (5-HD) blocked ouabain-induced ROS production and partially inhibited ouabain-induced increases in contractility in cardiac myocytes. Pre-incubation of myocytes with both 5-HD and PD98059 completely blocked ouabain's effect on contractility. Finally, we found that opening of mitochondrial KATP channel by diazoxide increased intracellular ROS and significantly raised contractility in cardiac myocytes. These new findings indicate that ouabain regulates cardiac contractility via both [Ca2+]i and ROS. While activation of MAPKs leads to increases in [Ca2+]i, opening of mitochondrial KATP channel relays the ouabain signal to increased ROS production in cardiac myocytes. 相似文献
8.
Xiantao Li Markus Rapedius Thomas Baukrowitz Gong Xin Liu D.K. Srivastava Jürgen Daut Peter J. Hanley 《Biochimica et Biophysica Acta (BBA)/General Subjects》2010
Background
5-Hydroxydecanoate (5-HD) inhibits preconditioning, and it is assumed to be a selective inhibitor of mitochondrial ATP-sensitive K+ (mitoKATP) channels. However, 5-HD is a substrate for mitochondrial outer membrane acyl-CoA synthetase, which catalyzes the reaction: 5?HD + CoA + ATP → 5-HD-CoA (5-hydroxydecanoyl-CoA) + AMP + pyrophosphate. We aimed to determine whether the reactants or principal product of this reaction modulate sarcolemmal KATP (sarcKATP) channel activity.Methods
Single sarcKATP channel currents were measured in inside-out patches excised from rat ventricular myocytes. In addition, sarcKATP channel activity was recorded in whole-cell configuration or in giant inside-out patches excised from oocytes expressing Kir6.2/SUR2A.Results
5-HD inhibited (IC50 ∼ 30 μM) KATP channel activity, albeit only in the presence of (non-inhibitory) concentrations of ATP. Similarly, when the inhibitory effect of 0.2 mM ATP was reversed by 1 μM oleoyl-CoA, subsequent application of 5-HD blocked channel activity, but no effect was seen in the absence of ATP. Furthermore, we found that 1 μM coenzyme A (CoA) inhibited sarcKATP channels. Using giant inside-out patches, which are weakly sensitive to “contaminating” CoA, we found that Kir6.2/SUR2A channels were insensitive to 5-HD-CoA. In intact myocytes, 5-HD failed to reverse sarcKATP channel activation by either metabolic inhibition or rilmakalim.General significance
SarcKATP channels are inhibited by 5-HD (provided that ATP is present) and CoA but insensitive to 5-HD-CoA. 5-HD is equally potent at “directly” inhibiting sarcKATP and mitoKATP channels. However, in intact cells, 5-HD fails to inhibit sarcKATP channels, suggesting that mitochondria are the preconditioning-relevant targets of 5-HD. 相似文献9.
Two K+
ATP channel blockers, 5-hydroxydecanoate (5-HD) and glyburide, are often used to study cross-talk between Na+/K+-ATPase and these channels. The aim of this work was to characterize the effects of these blockers on purified Na+/K+-ATPase as an aid to appropriate use of these drugs in studies on this cross-talk. In contrast to known dual effects (activating
and inhibitory) of other fatty acids on Na+/K+-ATPase, 5-HD only inhibited the enzyme at concentrations exceeding those that block mitochondrial K+
ATP channels. 5-HD did not affect the ouabain sensitivity of Na+/K+-ATPase. Glyburide had both activating and inhibitory effects on Na+/K+-ATPase at concentrations used to block plasma membrane K+
ATP channels. The findings justify the use of 5-HD as specific mitochondrial channel blocker in studies on the relation of this
channel to Na+/K+-ATPase, but question the use of glyburide as a specific blocker of plasma membrane K+
ATP channels, when the relation of this channel to Na+/K+-ATPase is being studied. 相似文献
10.
KATP channel openers have been shown to protect ischemic-reperfused myocardium by mimicking ischemic preconditioning, although their mechanisms of action have not been fully clarified. In this study we investigated the influence of the adenine nucleotide translocase (ANT) inhibitors–carboxyatractyloside (CAT) and bongkrekic acid (BA)–on the diazoxide- and pinacidil-induced uncoupling of isolated rat heart mitochondria respiring on pyruvate and malate (6 + 6 mM). We found that both CAT (1.3 M) and BA (20 M) markedly reduced the uncoupling of mitochondrial oxidative phosphorylation induced by the KATP channel openers. Thus, the uncoupling effect of diazoxide and pinacidil is evident only when ANT is not fixed by inhibitors in neither the C- nor the M-conformation. Moreover, the uncoupling effect of diazoxide and pinacidil was diminished in the presence of ADP or ATP, indicating a competition of KATP channel openers with adenine nucleotides. CAT also abolished K+-dependent mitochondrial respiratory changes. Thus ANT could also be involved in the regulation of KATP-channel-openers-induced K+ flux through the inner mitochondrial membrane. 相似文献
11.
Malgorzata Slocinska Jan Lubawy Wieslawa Jarmuszkiewicz Grzegorz Rosinski 《Journal of insect physiology》2013
In the present study, we describe the existence of mitochondrial ATP-dependent K+ channel (mitoKATP) in two different insect tissues, fat body and muscle of cockroach Gromphadorhina coquereliana. We found that pharmacological substances known to modulate potassium channel activity influenced mitochondrial resting respiration. In isolated mitochondria oxygen consumption increased by about 13% in the presence of potassium channel openers (KCOs) such as diazoxide and pinacidil. The opening of mitoKATP was reversed by glibenclamide (potassium channel blocker) and 1 mM ATP. Immunological studies with antibodies raised against the Kir6.1 and SUR1 subunits of the mammalian ATP-sensitive potassium channel, indicated the existence of mitoKATP in insect mitochondria. MitoKATP activation by KCOs resulted in a decrease in superoxide anion production, suggesting that protection against mitochondrial oxidative stress may be a physiological role of mitochondrial ATP-sensitive potassium channel in insects. 相似文献
12.
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). Vesicles of the inner mitochondrial membrane (mitoplasts) were prepared by hypoosmotic shock. Single-channel currents were measured by means of the patch-clamp technique. We identified an outward-rectifying channel with a slope conductance of 15 and 82 pS at negative and positive potentials, respectively. The block by 5-hydroxydecanoic acid and inhibition by ATP characterize this channel as the mtKATP channel. ATP also increased the frequency of events within the burst. This effect was modulated by the Ca2+-bath concentration. We also show that the human mtKATP channel is a direct target for nitric oxide that blocked the channel activity. Although the molecular structure of this channel type is still unknown, its characterization as an outward-rectifying channel and modulation by calcium ions and nitric oxide may help to elucidate its functional significance, which possibly implicates a role in cell survival after IPC. 相似文献
13.
The presynaptic dopamine (DA) D2 receptor-mediated regulation of ATP-sensitive potassium (K+
ATP) channels was examined in slices of the rat caudate-putamen. When slices were incubated with the specific D2 receptor antagonist (–)-sulpiride (SLP), a concentration-dependent increase of extracellular DA release was observed. SLP-induced enhancement was completely antagonized by coincubation with the K+
ATP channel opener diazoxide (DIA). Treatment of slices with the D2 receptor agonist quinpirole (QUI) almost completely inhibited DA outflow induced by the K+
ATP channel blocker butanedione-monoxime (BDM). Coincubation of SLP and guanosine triphosphate (GTP) or its non-hydrolizable analogue guanylyl-5-imidodiphosphate [Gpp(NH)p], significantly reduced the SLP-induced effect on DA levels. Furthermore, we observed that BDM-induced DA outflow was markedly inhibited by G protein activators suggesting an additional receptor-independent regulation of K+
ATP channel gating. Our results suggest that PTX-sensitive G proteins are involved in the signal transduction between D2 receptors and K+
ATP channels. Furthermore, K+
ATP channels can be modulated in a receptor-independent mechanism by G protein activators. 相似文献
14.
Bednarczyk P Kicińska A Kominkova V Ondrias K Dolowy K Szewczyk A 《The Journal of membrane biology》2004,199(2):63-72
The mitochondrial ATP-regulated potassium (mitoKATP) channel has been suggested as trigger and effector in myocardial ischemic preconditioning. However, molecular and pharmacological properties of the mitoKATP channel remain unclear. In the present study, single-channel activity was measured after reconstitution of the inner mitochondrial membrane from bovine ventricular myocardium into bilayer lipid membrane. After incorporation, a potassium-selective current was recorded with mean conductance of 103 ± 9 pS in symmetrical 150 mM KCl. Single-channel activity of this reconstituted protein showed properties of the mitoKATP channel: it was blocked by 500 μM ATP/Mg, activated by the potassium-channel opener diazoxide at 30 μM, inhibited by 50 μM glibenclamide or 150 μM 5-hydroxydecanoic acid, and was not affected by the plasma membrane ATP-regulated potassium-channel blocker HMR1098 at 100 μM. We observed that the mitoKATP channel was blocked by quinine in the micromolar concentration range. The inhibition by quinine was additionally verified with the use of 86Rb+ flux experiments and submitochondrial particles. Quinine inhibited binding of the sulfonylurea derivative [3H]glibenclamide to the inner mitochondrial membrane. We conclude that quinine inhibits the cardiac mitoKATP channel by acting on the mitochondrial sulfonylurea receptor.(P. Bednarczyk and A. Kicińska) These authors contributed equally to this work.This revised version was published online in August 2005 with a corrected cover date. 相似文献
15.
László Virág Tetsushi Furukawa Masayasu Hiraoka 《Molecular and cellular biochemistry》1993,119(1-2):209-215
The inside-out configuration of the patch-clamp technique was used to study the effect of glibenclamide on the ATP-sensitive K+ channel current in isolated guinea-pig ventricular myocytes. The inhibitory effect of glibenclamide was tested in the bath solution containing two different concentrations of ATP (100 M and 200 M). It was found that the effect of the drug on the KATP current was stronger in the presence of the higher concentration of ATP. The blocking effect of glibenclamide on the channels was weaker if, in addition to ATP, ADP was applied in the intracellular solution. Similarly, the inhibitory effect of the drug was not pronounced for the channels reactivated by ADP after run-down. As application of the drug in the presence and absence of Mg2+ did not show different effects on the channel inhibition, we concluded that the effect of glibenclamide may not depend on the phosphorylation of the channel protein. These results suggest that in addition of the previously described effect of ADP, ATP also has some modulatory effect on inhibition of the KATP channel by glibenclamide. 相似文献
16.
Sajal Chakraborti Animesh Chowdhury Pulak Kar Partha Das Soni Shaikh Soumitra Roy Tapati Chakraborti 《Archives of biochemistry and biophysics》2009,487(2):123-130
Treatment of bovine pulmonary smooth muscle cells with the TxA2 mimetic, U46619 stimulated [Ca2+]i, which was inhibited upon pretreatment with apocynin (NADPH oxidase inhibitor). Pretreatment with cromakalim (KV channel opener) or nifedepine (L-VOCC inhibitor) inhibited U46619 induced increase in [Ca2+]i, indicating a role of KV-LVOCC axis in this scenario. Neither cromakalim nor nifedepine inhibited U46619 induced increase in NADPH oxidase activity, suggesting that the NADPH oxidase activation is proximal to the KV-LVOCC axis in the cells. Pretreatment with calphostin C (PKC inhibitor) markedly reduced U46619 induced increase in NADPH oxidase activity and [Ca2+]i in the cells. Calphostin C pretreatment also markedly reduced p47phox phosphorylation and translocation to the membrane and association with p22phox, a component of Cyt.b558 of NADPH oxidase in the membrane. Overall, PKC plays an important role in NADPH oxidase derived O2−-mediated regulation of KV-LVOCC axis leading to an increase in [Ca2+]i by U46619 in the cells. 相似文献
17.
Diadenosine tetraphosphate (Ap4A) has been recently discovered in the pancreatic cells where targets ATP-sensitive K+ (KATP) channels, depolarizes the cell membrane and induces insulin secretion. However, whether Ap4A inhibit pancreatic KATP channels by targeting protein channel complex itself was unknown. Therefore, we coexpressed pancreatic KATP channel subunits, Kir6.2 and SUR1, in COS-7 cells and examined the effect of Ap4A on the single channel behavior using the inside-out configuration of the patch-clamp technique. Ap4A inhibited channel opening in a concentration-dependent manner. Analysis of single channels demonstrated that Ap4A did not change intraburst kinetic behavior of KATP channels, but rather decreased burst duration and increased between-burst duration. It is concluded that Ap4A antagonizes KATP channel opening by targeting channel subunits themselves and by keeping channels longer in closed interburst states. 相似文献
18.
The uncoupling protein and the potassium channel are activated by hyperosmotic stress in mitochondria from durum wheat seedlings 总被引:4,自引:0,他引:4
D. TRONO Z. FLAGELLA M. N. LAUS N. DI FONZO & D. PASTORE 《Plant, cell & environment》2004,27(4):437-448
The plant uncoupling mitochondrial protein (PUMP) and the plant mitochondrial potassium channel (PmitoKATP) are two recently discovered energy‐dissipating systems present in plant mitochondria, which may play a role as defence systems under environmental stress. To verify whether hyperosmotic stress affects the two dissipating systems in durum wheat (Triticum durum Desf.), their functioning was studied in early etiolated seedlings maintained under moderate and severe salt (NaCl) and osmotic (mannitol) stress. As measures of mitochondrial stress mitochondrial integrity, membrane potential maintenance and oxygen uptake coupled with ATP synthesis during succinate and proline oxidation were investigated. Both PUMP and PmitoKATP were activated under stress conditions. Activation was clearly evident even under moderate stress when proline oxidation was inhibited, although mitochondrial integrity and succinate oxidation were still unaffected. Under severe stress, which significantly affected all the tested indicators of mitochondrial integrity and functionality, PUMP and PmitoKATP activation was further enhanced. Interestingly, both systems were activated by reactive oxygen species and were able to control mitochondrial superoxide anion production. These results suggest that PUMP and PmitoKATP serve as early antioxidant defence systems in response to hyperosmotic stress and that they are involved in a prolonged response to stress. 相似文献
19.
The G-protein-mediated coupling of a glucagon receptor to ATP-dependent K channels—KATP—has been studied in insulin-secreting cells using the patch clamp technique. In excised outside-out patches, KATP channel activity was inhibited by low concentrations of glucagon (IC50 = 2.4 nm); the inhibitory effect vanished at concentrations greater than 50 nm. In cell-attached patches, inhibition by bath-applied glucagon was seen most often, although stimulation was observed in a few cases. A dual action of the hormone is proposed to resolve these apparently divergent results. In excised inside-out patches, KATP channel activity was inhibited by addition of subunits purified from either erythrocyte or retina (IC50 = 50 pm and 1 nm, respectively). Subsequent exposure of the patch to
i
or
o
reversed this effect. In excised inside-out patches, increasing Mg2+ in the bath stimulated the channel activity between 0 and 0.5 mm, but blocked it at higher concentrations (IC50 = 2.55 mm). In most cases (70%), GTP had a stimulatory effect at concentrations up to 100 m. However, in three cases, similar GTP levels had clear inhibitory effects. In excised inside-out patches, cholera toxin (CTX) caused channel inhibition. Although the effect could not be reversed by removal of the toxin, the activity was restored by subsequent addition of purified
i
or
o
. These results are compatible with a model whereby channel inhibition by activated G
S
-coupled receptors occurs, at least in part, via association of the subunits of G
S
with
i
/
o
subunits and deactivation of the
i
/
o
-dependent stimulatory pathway. On the basis of this hypothesis, a model is developed to describe the effects of G proteins on the KATP channel, as well as to account for the concentration-dependent stimulation and inhibition of KATP channel by Mg2+. An interpretation of the ability of glucagon to potentiate, but not initiate, insulin release is also given in terms of this model and the effects of ATP on KATP channels.This work was supported by grant DCB-89 19368 from the National Science Foundation and a research grant (W-P 880513) from the American Diabetes Association to B.R.The authors would like to thank Dr. A.E. Boyd, III for supplying the RINm5F and HIT cells, Drs. J. Codina and L. Birnbaumer for supplying the G protein and subunits from erythrocyte, Dr. R.A. Cerione for supplying the G protein subunit from retina, and Mrs. Satoko Hagiwara for preparing and maintaining the cell cultures. 相似文献
20.
Adam Szewczyk Aneta Czyż Grażyna Wójcik Lech Wojtczak Maciej J. Nałecz 《Journal of bioenergetics and biomembranes》1996,28(2):147-152
Mitochondria from several tissues contain a potassium-specific channel similar to the ATP-regulated K+ (KATP) channel of the plasma membrane. The mitochondrial channel shares with the plasma membrane KATP channel the sensitivity to sulfonylurea derivatives and some other blockers as well as to channel openers of diverse chemical character. In contrast to the plasma membrane channel, which is blocked by free ATP, the mitochondrial KATP channel reconstituted into liposomes requires the ATP-Mg complex for inhibition. The mitochondrial KATP channel, possibly in a concerted action with other K+ permeability pathways, plays an important role in mitochondrial volume control. Its function in the regulation of the components of the protonmotive force is also suggested. 相似文献