Vanadate as an activator of ATP ? sensitive potassium channels in mouse skeletal muscle

Neumcke, B.; Weik, R.

doi:10.1007/bf00185452

Cited by 12 publications

(8 citation statements)

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“…Ki and the Hill coefficient were 21 ASM and 1.9, respectively, in mdx muscle, values which could be considered not significantly different from those for normal muscle. Similar values have been found for Ki in frog muscle (Davies, Standen & Stanfield, 1992), in mouse and rat skeletal muscle (Neumcke & Weik, 1991;McKillen et al 1994) and in rat ventricular myocytes (Findlay, 1988; Lederer & Nichols, 1989). A Hill coefficient close to 2 has also been reported in mouse muscle (Neumcke & Weik, 1991) and in rat ventricular myocytes (Findlay, 1988;Lederer & Nichols, 1989).…”

Section: Discussionsupporting

confidence: 74%

“…Figure 3B shows the dose dependence of inhibition of KATP channels in normal and mdx muscle cells. Channel activity was expressed as a fraction of that in the absence of ATP and the normalized data were fitted by a Hill equation: (Davies, Standen & Stanfield, 1992), in mouse and rat skeletal muscle (Neumcke & Weik, 1991;McKillen et al 1994) and in rat ventricular myocytes (Findlay, 1988; Lederer & Nichols, 1989). A Hill coefficient close to 2 has also been reported in mouse muscle (Neumcke & Weik, 1991) and in rat ventricular myocytes (Findlay, 1988;Lederer & Nichols, 1989 Hocherman & Bezanilla (1996).…”

Section: Resultsmentioning

confidence: 96%

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Similarity of ATP‐dependent K+ channels in skeletal muscle fibres from normal and mutant mdx mice.

Allard

Rougier

1997

The Journal of Physiology

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1. ATP-dependent K+ (KATP) channels were studied in fibres isolated from flexor digitorum brevis and interosseal skeletal muscles of normal and mutant mdx mice using the patch clamp technique in the presence of asymmetrical K+ concentrations (5 mm K+ in the pipette and in vivo intracellular [K+] or 145 mm K+ at the cytoplasmic face). 2. In cell-attached patches from mdx muscle fibres bathed in K+-rich solution, cell poisoning with fluorodinitrobenzene induced partially reversible opening of channels carrying an outward current of an amplitude of 1P2 pA at 0 mV. Exposure of fibres to the K+ channel opener cromakalim led to opening of the same type of channel. These channels were assumed to be KATP channels. 3. On excision of inside-out patches from mdx muscle fibres, in the absence of intracellular ATP, KATP channels were active: they carried a unitary outward current of 1 6 pA at 0 mV and were inhibited by intracellular ATP and glibenclamide. The number of KATP channels per patch was not significantly different in muscles from normal and mdx mice.4. In inside-out patches, in the presence of 1 mm intracellular Mg2+, slope conductances of 21 and 203 pS were found for KATP channels in normal and mdx muscle, respectively. In the absence of Mg2+, slope conductances of KATP channels were 31-3 and 32 pS in normal and mdx muscle, respectively and KATP channel activity was' augmented in mdx muscle in the same way as in normal muscle. Activity of the same KATP channel was observed in extensor digitorum longus muscle from normal and mdx mice. 5. In inside-out patches held at 0 mV, the relationship between KATP channel activity and intracellular ATP was described by a Hill equation: K1 values were 23 and 21 /SM and Hill coefficients were 1 8 and 1'9 in normal and mdx muscle, respectively. 6. These results indicate that the distribution, the conductance properties and ATP sensitivity of KATP channels do not differ in normal and in mdx mouse skeletal muscle.

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Section: Discussionsupporting

confidence: 74%

Section: Resultsmentioning

confidence: 96%

Similarity of ATP‐dependent K+ channels in skeletal muscle fibres from normal and mutant mdx mice.

Allard

Rougier

1997

The Journal of Physiology

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“…In three other patches to which we applied external gluconate, we were also unable to detect any channel activation. opener RP 49356 in cardiac muscle have all been reported to act in this way (Thuringer & Escande, 1989;Davies, 1990;Neumcke & Weik, 1991;Davies et al 1992). In contrast, intracellular gluconate caused channel activation without affecting channel inhibition by ATP.…”

Section: Properties Of Katp Channels From the Rat Fdb Musclementioning

confidence: 99%

“…To measure the concentration dependence of channel inhibition by ATP we applied ATP at concentrations between 3 and 1000 UM, and measured NPopen over a 0 0 1 10 100 1000 (Neumcke & Weik, 1991) and 17 ,UM in frog (Davies, Standen & Stanfield, 1992 Figure ID shows the The effect of gluconate on channel run-down…”

Section: Properties Of Katp Channels From the Rat Fdb Musclementioning

confidence: 99%

The effect of intracellular anions on ATP‐dependent potassium channels of rat skeletal muscle.

McKillen

Davies

Stanfield

et al. 1994

The Journal of Physiology

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1. We have used excised inside-out patches to study the effects of anions bathing the cytoplasmic surface of the membrane on ATP-dependent K+ channels of rat flexor digitorum brevis muscle. Channels were closed by ATP applied to the cytoplasmic face of the patch with a concentration for half-closure (K1) of 14 ,UM, were highly selective for K+ and had unitary conductances of 62 pS in symmetrical 155 mm K+ and 27 pS in 5 mM[K+]o.2. In 139 mm Cl-internal solution channel activity declined rapidly after excision of the patch. Inclusion of 40 mm potassium gluconate (substituted for KCl) in the solution both restored channel activity and greatly slowed its subsequent run-down. 3. The action of gluconate was concentration dependent. The effect did not involve a change in ATP binding, since the K1 for ATP was not significantly changed by gluconate, and was specific for the cytoplasmic face of the patch. 4. The anions pyruvate, lactate and acetate were all able to restore channel activity after run-down, though less well than gluconate, while sulphate and methylsulphate were without effect. 5. Analysis of single channel kinetics showed that gluconate did not affect mean open lifetime, but led to a decrease in the number and duration of long closings. 6. Anions are most likely to act by stabilizing the structure of the channel protein.

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“…It has been reported to enhance the activity of K ATP channels in skeletal muscle (24) and in ventricular myocytes (25), but it had no effect on the cloned K ATP channel Kir6.2/ SUR1 in the presence of magnesium nucleotides (16). One explanation for these disparate findings is that different types of K ATP channel exhibit different sensitivities to vanadate.…”

mentioning

confidence: 99%

Interaction of Vanadate with the Cloned Beta Cell KATP Channel

Proks¹,

Ashfield

Ashcroft

1999

Journal of Biological Chemistry

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Vanadate is used as a tool to trap magnesium nucleotides in the catalytic site of ATPases. However, it has also been reported to activate ATP-sensitive potassium (K ATP ) channels in the absence of nucleotides. K ATP channels comprise Kir6.2 and sulfonylurea receptor subunits (SUR1 in pancreatic beta cells, SUR2A in cardiac and skeletal muscle, and SUR2B in smooth muscle). We explored the effect of vanadate (2 mM ATP-sensitive potassium (K ATP )1 channels are found in a variety of tissues where they couple changes in cellular metabolism to electrical activity and potassium fluxes (1-3). Molecular cloning of these channels has revealed that they consist of two distinct types of subunit (a pore-forming subunit (Kir6.2) and a sulfonylurea receptor subunit (SUR1 in pancreatic beta cells, SUR2A in cardiac and skeletal muscle, and SUR2B in smooth muscle)) that associate in a 4:4 stoichiometry to form an octameric K ATP channel. (4 -12). The sulfonylurea receptor subunit belongs to the ATP-binding cassette (ABC) transporter family and is characterized by multiple transmembrane domains and two large cytosolic loops that contain consensus sequences for nucleotide binding and hydrolysis (4,13 Vanadate is routinely used as a tool to trap magnesium nucleotides in the catalytic site of ATPases. ADP is trapped by vanadate both as a result of ATP hydrolysis and also when it is added directly to the solution (22). This is likely to be because orthovanadate acts as an analogue of phosphate. Among eukaryotic ABC transporters, vanadate trapping has been demonstrated for both MDR (18) and MRP (19). Photoaffinity labeling experiments with 8-azido-[ 32 P]ATP have revealed that ATP binds with high affinity to NBD1 of SUR1 and that MgADP binds to NBD2 (23). Unlike other ABC transporters, however, nucleotide binding to SUR1 is not enhanced by vanadate (23).The effects of vanadate on K ATP channel currents are variable. It has been reported to enhance the activity of K ATP channels in skeletal muscle (24) and in ventricular myocytes (25), but it had no effect on the cloned K ATP channel Kir6.2/ SUR1 in the presence of magnesium nucleotides (16). One explanation for these disparate findings is that different types of K ATP channel exhibit different sensitivities to vanadate. Another reason may be that vanadate interacts with a third protein, not present in the heterologous expression system, to modulate K ATP channel activity. A third possibility is that, because vanadate exists in solution in a number of different polymeric forms (e.g. orthovanadate and decavanadate), the concentration of the different vanadate complexes might vary in the experimental solutions used by different investigators.In this paper, we examine the effects of orthovanadate and decavanadate on the activity of cloned K ATP channels containing different types of SUR subunit, heterologously expressed in Xenopus oocytes. We show that the major effects of vanadate on K ATP channel activity are mediated via the sulfonylurea receptor subunit, with different SURs producin...

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Vanadate as an activator of ATP ? sensitive potassium channels in mouse skeletal muscle

Cited by 12 publications

References 12 publications

Similarity of ATP‐dependent K+ channels in skeletal muscle fibres from normal and mutant mdx mice.

Similarity of ATP‐dependent K+ channels in skeletal muscle fibres from normal and mutant mdx mice.

The effect of intracellular anions on ATP‐dependent potassium channels of rat skeletal muscle.

Interaction of Vanadate with the Cloned Beta Cell KATP Channel

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