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Cardioselectivity of the sulphonylurea HMR 1098: studies on native and recombinant cardiac and pancreatic K(ATP) channels.

ABSTRACT: In this study we investigated the effects of the putative cardioselective sulphonylurea derivative HMR 1098 on ATP-sensitive potassium (K(ATP)) channels from cardiac ventricular myocytes, the INS-1 beta-cell line and from recombinant K(ATP) channels composed of SUR2A/Kir6.2, SUR1/Kir6.2, SUR1/Kir6.1 an Kir6.2,DeltaC26. Recombinant channels were expressed in tsA201 or COS-1 cells. The effects of HMR 1098 on single channel and whole-cell currents were recorded using the patch-clamp technique. At the single channel level, using excised inside-out membrane patches, HMR 1098 inhibited K(ATP) channels from ventricular cells and INS-1 cells with IC(50)s of 0.88 and 720 microM respectively. Similar results to those in cardiac cells were obtained using recombinant SUR2A/Kir6.2 K(ATP) channels. HMR 1098 inhibition of SUR2A/Kir6.2 K(ATP) channels was unaffected by the presence of internal ADP. In whole-cell recordings, HMR 1098 inhibited SUR2A/Kir6.2 and SUR1/Kir6.2 currents with IC(50)s of 2.1 and 860 microM respectively. HMR 1098 was without effect on currents either from the Kir6.2,DeltaC26 truncation mutant or from Kir2.1. Our results demonstrate that HMR 1098 is a selective inhibitor of cardiac K(ATP) channels, showing a 400 - 800-fold selectivity over beta-cell K(ATP) channels. The non-aromatic substitutions in the sulphonylurea moiety greatly increase the cardioselectivity of this compound while reducing the overall blocking potency of this sulphonylurea derivative.

SUBMITTER: Manning Fox JE

PROVIDER: S-EPMC1573135 | biostudies-literature | 2002 Jan

REPOSITORIES: biostudies-literature

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Cardioselectivity of the sulphonylurea HMR 1098: studies on native and recombinant cardiac and pancreatic K(ATP) channels.

Manning Fox Jocelyn E JE Kanji Hussein D HD French Robert J RJ Light Peter E PE

British journal of pharmacology 20020101 2

In this study we investigated the effects of the putative cardioselective sulphonylurea derivative HMR 1098 on ATP-sensitive potassium (K(ATP)) channels from cardiac ventricular myocytes, the INS-1 beta-cell line and from recombinant K(ATP) channels composed of SUR2A/Kir6.2, SUR1/Kir6.2, SUR1/Kir6.1 an Kir6.2,DeltaC26. Recombinant channels were expressed in tsA201 or COS-1 cells. The effects of HMR 1098 on single channel and whole-cell currents were recorded using the patch-clamp technique. At t ...[more]

PMID: 11815384

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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:A-type voltage-gated K(+) (Kv) channels self-regulate their activity by inactivating directly from the open state (open-state inactivation [OSI]) or by inactivating before they open (closed-state inactivation [CSI]). To determine the inactivation pathways, it is often necessary to apply several pulse protocols, pore blockers, single-channel recording, and kinetic modeling. However, intrinsic hurdles may preclude the standardized application of these methods. Here, we implemented a simple method inspired by earlier studies of Na(+) channels to analyze macroscopic inactivation and conclusively deduce the pathways of inactivation of recombinant and native A-type Kv channels. We investigated two distinct A-type Kv channels expressed heterologously (Kv3.4 and Kv4.2 with accessory subunits) and their native counterparts in dorsal root ganglion and cerebellar granule neurons. This approach applies two conventional pulse protocols to examine inactivation induced by (a) a simple step (single-pulse inactivation) and (b) a conditioning step (double-pulse inactivation). Consistent with OSI, the rate of Kv3.4 inactivation (i.e., the negative first derivative of double-pulse inactivation) precisely superimposes on the profile of the Kv3.4 current evoked by a single pulse because the channels must open to inactivate. In contrast, the rate of Kv4.2 inactivation is asynchronous, already changing at earlier times relative to the profile of the Kv4.2 current evoked by a single pulse. Thus, Kv4.2 inactivation occurs uncoupled from channel opening, indicating CSI. Furthermore, the inactivation time constant versus voltage relation of Kv3.4 decreases monotonically with depolarization and levels off, whereas that of Kv4.2 exhibits a J-shape profile. We also manipulated the inactivation phenotype by changing the subunit composition and show how CSI and CSI combined with OSI might affect spiking properties in a full computational model of the hippocampal CA1 neuron. This work unambiguously elucidates contrasting inactivation pathways in neuronal A-type Kv channels and demonstrates how distinct pathways might impact neurophysiological activity.

Dataset Information

Cardioselectivity of the sulphonylurea HMR 1098: studies on native and recombinant cardiac and pancreatic K(ATP) channels.

Publications

Cardioselectivity of the sulphonylurea HMR 1098: studies on native and recombinant cardiac and pancreatic K(ATP) channels.

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