The Stereoenantiomers of a Pinacidil Analog Open or Close Cloned ATP-sensitive K+ Channels

Abstract

ATP-dependent K؉ channels (K ATP channels) are composed of pore-forming subunits Kir6.x and sulfonylurea receptors (SURs). Cyanoguanidines such as pinacidil and P1075 bind to SUR and enhance MgATP binding to and hydrolysis by SUR, thereby opening K ATP channels. In the vasculature, openers of K ATP channels produce vasorelaxation. Some novel cyanoguanidines, however, selectively reverse opener-induced vasorelaxation, suggesting that they might be K ATP channel blockers. Here we have analyzed the interaction of the enantiomers of a racemic cyanoguanidine blocker, PNU-94750, with Kir6.2/SUR channels. In patch clamp experiments, the R-enantiomer (PNU-96293) inhibited Kir6.2/SUR2 channels (IC 50 ϳ50 nM in the whole cell configuration), whereas the S-enantiomer (PNU-96179) was a weak opener. Radioligand binding studies showed that the R-enantiomer was more potent and that it was negatively allosterically coupled to MgATP binding, whereas the S-enantiomer was weaker and positively coupled. Binding experiments also suggested that both enantiomers bound to the P1075 site of SUR. This is the first report to show that the enantiomers of a K ATP channel modulator affect channel activity and coupling to MgATP binding in opposite directions and that these opposite effects are apparently mediated by binding to the same (opener) site of SUR.

The protective effect of ursodeoxycholic acid in an in vitro model of the human fetal heart occurs via targeting cardiac fibroblasts

“…Another agent used in the present study, P1075 is a more potent analogue of pinacidil (Lange et al, 2002).…”

“…Similar results were obtained under normoxic conditions with 1 μM UDCA. To further evaluate potential molecular targets responsible for the UDCA-mediated negative shift (hyperpolarisation) in membrane potential observed in human fetal fibroblasts, selective K ATP channel agents were employed (Lange et al, 2002). Addition of K ATP channel agonists induces efflux of K + from the cells, lowering the membrane potential to more negative values Lange et al, 2002;Shibukawa et al, 2005).…”

“…To further evaluate potential molecular targets responsible for the UDCA-mediated negative shift (hyperpolarisation) in membrane potential observed in human fetal fibroblasts, selective K ATP channel agents were employed (Lange et al, 2002). Addition of K ATP channel agonists induces efflux of K + from the cells, lowering the membrane potential to more negative values Lange et al, 2002;Shibukawa et al, 2005). It was shown previously that treatment with the K ATP channel blocker glibenclamide prevented UDCA induced hyperpolarisation of RMP in neonatal rat fibroblasts (Miragoli et al, 2011a).…”

Incomplete dissociation of glibenclamide from wild‐type and mutant pancreatic KATP channels limits their recovery from inhibition

“…However, amphiphilic inhibitors with weaker affinity show unblocking of K ATP channels in the whole‐cell configuration with a time course of 1–5 min and without apparent sigmoidicity. For example, the unblocking of K IR 6.1/SUR2B from PNU96296 (Lange et al. , 2002) and K IR 6.1/SUR2B from the glibenclamide congener, HMR 1883 (100 µmol·L −1 ; Russ et al.…”

Pharmacological characterization of a 1,4‐dihydropyridine analogue, 9‐(3,4‐dichlorophenyl)‐3,3,6,6‐tetramethyl‐3,4,6,7,9,10‐hexahydro‐1,8(2H,5H)‐acridinedione (A‐184209) as a novel KATP channel inhibitor

“…More recently, it has also been demonstrated that the enantiomers of a K ATP channel modulator PNU‐94750 affected channel activity and coupling to MgATP in opposite directions with the ( R )‐enantiomer inhibiting SUR2–Kir6.2 channels whereas the ( S )‐enantiomer behaving as a weak opener. Interestingly, these opposite effects were apparently mediated by binding to the same site on the sulfonylurea receptor (Lange et al ., 2002).…”