Mechanism of action of a K+ channel activator BRL 38227 on ATP-sensitive K+ channels in mouse skeletal muscle fibres.
1. Investigations were made into the effects of BRL 38227, a potassium channel activator, on ATP-sensitive potassium channels (K+ATP channels) in single fibres dissociated from the flexor digitorum brevis muscle of C57BL/6J mice. 2. In cell-attached patches BRL 38227 (100 microM) caused activation of a glibenclamide-sensitive potassium current. Linear slope conductance of the inward current, partial rectification of the outward current and glibenclamide sensitivity indicate that K+ATP channels are the site of action of BRL 38227. 3. In the absence of ATP at the cytoplasmic side of excised inside-out patches, BRL 38227 caused direct and magnesium-dependent activation of K+ATP channels. The degree of activation diminished with successive applications of BRL 38227. 4. BRL 38227 also caused activation of K+ATP channels in the presence of low (< 100 microM) but not high (1.0 mM) ATP, particularly in patches containing large numbers of channels. 5. BRL 38227 and 5 microM MgATP failed to activate channels following complete run-down. 6. Results show that BRL 38227 caused direct activation of K+ATP in skeletal muscle and that this was mediated through a magnesium-dependent binding site rather than alleviation of inhibition by competitive displacement of ATP from the inhibitory site.
Hussain
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Division of Neuroscience, School of Biological Sciences, University of Manchester.
Wareham
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D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000818:Animals; D001578:Benzopyrans / Q000494:pharmacology*; D019806:Cromakalim; D005260:Female; D005905:Glyburide / Q000494:pharmacology; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018485:Muscle Fibers, Skeletal / Q000187:drug effects / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000187:drug effects / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000187:drug effects*; D011758:Pyrroles / Q000494:pharmacology*
D001578:Benzopyrans; D015221:Potassium Channels; D011758:Pyrroles; D019806:Cromakalim; D000255:Adenosine Triphosphate; D005905:Glyburide