Dataset Information

Glimepiride block of cloned beta-cell, cardiac and smooth muscle K(ATP) channels.

ABSTRACT: 1. We examined the effect of the sulphonylurea glimepiride on three types of recombinant ATP-sensitive potassium (K(ATP)) channels. 2. K(ATP) channels share a common pore-forming subunit, Kir6.2, which associates with different sulphonylurea receptor isoforms (SUR1 in beta-cells, SUR2A in heart and SUR2B in smooth muscle). 3. Kir6.2 was coexpressed with SUR1, SUR2A or SUR2B in Xenopus oocytes and macroscopic K(ATP) currents were recorded from giant inside-out membrane patches. Glimepiride was added to the intracellular membrane surface. 4. Glimepiride inhibited Kir6.2/SUR currents by interaction with two sites: a low-affinity site on Kir6.2 (IC(50)= approximately 400 microM) and a high-affinity site on SUR (IC(50)=3.0 nM for SUR1, 5.4 nM for SUR2A and 7.3 nM for SUR2B). The potency of glimepiride at the high-affinity site is close to that observed for glibenclamide (4 nM for SUR1, 27 nM for SUR2A), which has a similar structure. 5. Glimepiride inhibition of Kir6.2/SUR2A and Kir6.2/SUR2B currents, but not Kir6.2/SUR1 currents, reversed rapidly. 6. Our results indicate that glimepiride is a high-affinity sulphonylurea that does not select between the beta-cell, cardiac and smooth muscle types of recombinant K(ATP) channel, when measured in inside-out patches. High-affinity inhibition is mediated by interaction of the drug with the sulphonylurea receptor subunit of the channel.

SUBMITTER: Song DK

PROVIDER: S-EPMC1572773 | biostudies-literature | 2001 May

REPOSITORIES: biostudies-literature

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Glimepiride block of cloned beta-cell, cardiac and smooth muscle K(ATP) channels.

Song D K DK Ashcroft F M FM

British journal of pharmacology 20010501 1

1. We examined the effect of the sulphonylurea glimepiride on three types of recombinant ATP-sensitive potassium (K(ATP)) channels. 2. K(ATP) channels share a common pore-forming subunit, Kir6.2, which associates with different sulphonylurea receptor isoforms (SUR1 in beta-cells, SUR2A in heart and SUR2B in smooth muscle). 3. Kir6.2 was coexpressed with SUR1, SUR2A or SUR2B in Xenopus oocytes and macroscopic K(ATP) currents were recorded from giant inside-out membrane patches. Glimepiride was ad ...[more]

PMID: 11325810

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Project description:ATP-sensitive potassium channels (KATP channels) are hetero-octameric nucleotide-gated ion channels that couple cellular metabolism to excitability in various tissues. In the heart, KATP channels are activated during ischaemia and potentially during adrenergic stimulation. In the vasculature, they are normally active at a low level, reducing vascular tone, but the ubiquitous nature of these channels leads to complex and poorly understood channelopathies as a result of gain- or loss-of-function mutations. Zebrafish (ZF) models of these channelopathies may provide insights to the link between molecular dysfunction and complex pathophysiology, but this requires understanding the tissue dependence of channel activity and subunit specificity. Thus far, direct analysis of ZF KATP expression and functional properties has only been performed in pancreatic β-cells. Using a comprehensive combination of genetically modified fish, electrophysiology and gene expression analysis, we demonstrate that ZF cardiac myocytes (CM) and vascular smooth muscle (VSM) express functional KATP channels of similar subunit composition, structure and metabolic sensitivity to their mammalian counterparts. However, in contrast to mammalian cardiovascular KATP channels, ZF channels are insensitive to potassium channel opener drugs (pinacidil, minoxidil) in both chambers of the heart and in VSM. The results provide a first characterization of the molecular properties of fish KATP channels and validate the use of such genetically modified fish as models of human Cantú syndrome and ABCC9-related Intellectual Disability and Myopathy syndrome. KEY POINTS: Zebrafish cardiac myocytes (CM) and vascular smooth muscle (VSM) express functional KATP channels of similar subunit composition, structure and metabolic sensitivity to their mammalian counterparts. In contrast to mammalian cardiovascular KATP channels, zebrafish channels are insensitive to potassium channel opener drugs (pinacidil, minoxidil) in both chambers of the heart and in VSM. We provide a first characterization of the molecular properties of fish KATP channels and validate the use of such genetically modified fish as models of human Cantú syndrome and ABCC9-related Intellectual Disability and Myopathy syndrome.

Project description:Voltage-dependent L-type (Ca(V)1.2) Ca(2+) channels are a heteromeric complex formed from pore-forming alpha(1) and auxiliary alpha(2)delta and beta subunits. Ca(V)1.2 channels are the principal Ca(2+) influx pathway in arterial myocytes and regulate multiple physiological functions, including contraction. The macromolecular composition of arterial myocyte Ca(V)1.2 channels remains poorly understood, with no studies having examined the molecular identity or physiological functions of alpha(2)delta subunits.We investigated the functional significance of alpha(2)delta subunits in myocytes of resistance-size (100 to 200 mum diameter) cerebral arteries.alpha(2)delta-1 was the only alpha(2)delta isoform expressed in cerebral artery myocytes. Pregabalin, an alpha(2)delta-1/-2 ligand, and an alpha(2)delta-1 antibody, inhibited Ca(V)1.2 currents in isolated myocytes. Acute pregabalin application reversibly dilated pressurized arteries. Using a novel application of surface biotinylation, data indicated that >95% of Ca(V)1.2 alpha(1) and alpha(2)delta-1 subunits were present in the arterial myocyte plasma membrane. Alpha(2)delta-1 knockdown using short hairpin RNA reduced plasma membrane-localized Ca(V)1.2 alpha(1) subunits, caused a corresponding elevation in cytosolic Ca(V)1.2 alpha(1) subunits, decreased intracellular Ca(2+) concentration, inhibited pressure-induced vasoconstriction ("myogenic tone"), and attenuated pregabalin-induced vasodilation. Prolonged (24-hour) pregabalin exposure did not alter total alpha(2)delta-1 or Ca(V)1.2 alpha(1) proteins but decreased plasma membrane expression of each subunit, which reduced myogenic tone.alpha(2)delta-1 is essential for plasma membrane expression of arterial myocyte Ca(V)1.2 alpha(1) subunits. alpha(2)delta-1 targeting can block Ca(V)1.2 channels directly and inhibit surface expression of Ca(V)1.2 alpha(1) subunits, leading to vasodilation. These data identify alpha(2)delta-1 as a novel molecular target in arterial myocytes, the manipulation of which regulates contractility.

Dataset Information

Glimepiride block of cloned beta-cell, cardiac and smooth muscle K(ATP) channels.

Publications

Glimepiride block of cloned beta-cell, cardiac and smooth muscle K(ATP) channels.

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