Pharmaco-topology of Sulfonylurea Receptors

Abstract

The differential responsiveness of (SUR1/KIR6.2)4 pancreatic β-cellversus (SUR2A/KIR6.2)4 sarcolemmal or (SUR2B/KIR6.0)4 smooth muscle cellK ATP channels to K+ channel openers (KCOs) is the basis for the selective prevention of hyperinsulinemia, myocardial infarction, and acute hypertension. KCO-stimulation ofK ATP channels is a unique example of functional coupling between a transport ATPase and a K+ inward rectifier. KCO binding to SUR is Mg-ATP-dependent and antagonizes the inhibition of (KIR6.0)4 pore opening by nucleotides. Patch-clamping of matched chimeric human SUR1-SUR2A/KIR6.2 channels was used to identify the SUR regions that specify the selective response of sarcolemmalversus β-cell channels to cromakalim or pinacidilversus diazoxide. The SUR2 segment containing the 12th through 17th predicted transmembrane domains, TMD12–17, confers sensitivity to the benzopyran, cromakalim, and the pyridine, pinacidil, whereas an SUR1 segment which includes TMD6–11 and the first nucleotide-binding fold, NBF1, controls responsiveness to the benzothiadiazine, diazoxide. These data are incorporated into a functional topology model for the regulatory SUR subunits ofK ATP channels. The differential responsiveness of (SUR1/KIR6.2)4 pancreatic β-cellversus (SUR2A/KIR6.2)4 sarcolemmal or (SUR2B/KIR6.0)4 smooth muscle cellK ATP channels to K+ channel openers (KCOs) is the basis for the selective prevention of hyperinsulinemia, myocardial infarction, and acute hypertension. KCO-stimulation ofK ATP channels is a unique example of functional coupling between a transport ATPase and a K+ inward rectifier. KCO binding to SUR is Mg-ATP-dependent and antagonizes the inhibition of (KIR6.0)4 pore opening by nucleotides. Patch-clamping of matched chimeric human SUR1-SUR2A/KIR6.2 channels was used to identify the SUR regions that specify the selective response of sarcolemmalversus β-cell channels to cromakalim or pinacidilversus diazoxide. The SUR2 segment containing the 12th through 17th predicted transmembrane domains, TMD12–17, confers sensitivity to the benzopyran, cromakalim, and the pyridine, pinacidil, whereas an SUR1 segment which includes TMD6–11 and the first nucleotide-binding fold, NBF1, controls responsiveness to the benzothiadiazine, diazoxide. These data are incorporated into a functional topology model for the regulatory SUR subunits ofK ATP channels. K+channel opener sulfonylurea receptor (SURx/KIR6.0)4channels nucleotide binding fold IC50 value for ATP the maximal mean open channel probability in the absence of nucleotides transmembrane domain K+ channel openers, KCOs,1 are a structurally diverse group of compounds with no obvious common pharmacophore linking their ability to antagonize the inhibition of ATP-sensitive K+ (K ATP) channels by intracellular nucleotides (1.Edwards G. Weston A.H. Annu. Rev. Pharmacol. Toxicol. 1993; 33: 597-637Crossref PubMed Scopus (529) Google Scholar). After the identification ofK ATP channels in cardiomyocytes and pancreatic β-cells using the patch-clamp technique (2.Noma A. Nature. 1983; 305: 147-148Crossref PubMed Scopus (1978) Google Scholar, 3.Cook D.L. Hales C.N. Nature. 1984; 311: 271-273Crossref PubMed Scopus (976) Google Scholar), Trube et al. (4.Trube G. Rorsman P. Ohno-Shosaku T. Pfluegers Arch. Eur. J. Physiol. 1986; 407: 493-499Crossref PubMed Scopus (527) Google Scholar) showed the benzothiadiazine KCO, diazoxide, stimulates β-cell K ATP channels, and Escande et al. (5.Escande D. Thuringer D. Leguern S. Cavero I. Biochem Biophys. Res. Commun. 1988; 154: 620-625Crossref PubMed Scopus (175) Google Scholar) reported the benzopyran KCO, cromakalim, increased the activity of sarcolemmal channels in inside-out membrane patches indicating a direct interaction with these channels. Cloning of β-cell and sarcolemmal K ATP channel subunits led to the understanding that they are (SUR1/KIR6.2)4 and (SUR2A/KIR6.2)4 complexes, respectively, and that their differential responses to KCOs and to sulfonylureas are determined by the SUR isoform (Refs. 6.Aguilar-Bryan L. Nichols C.G. Wechsler S.W. Clement J.P., IV Boyd III, A.E. Gonzalez G. Herrera-Sosa H. Nguy K. Bryan J. Nelson D.A. Science. 1995; 268: 423-426Crossref PubMed Scopus (1289) Google Scholar, 7.Inagaki N. Gonoi T. Clement J.P., IV Namba N. Inazawa J. Gonzalez G. Aguilar-Bryan L. Seino S. Bryan J. Science. 1995; 270: 1166-1170Crossref PubMed Scopus (1623) Google Scholar, 8.Inagaki N. Gonoi T. Clement J.P., IV Wang C.Z. Aguilar-Bryan L. Bryan J. Seino S. Neuron. 1996; 16: 1011-1017Abstract Full Text Full Text PDF PubMed Scopus (880) Google Scholar, and reviewed in Ref. 9.Babenko A.P. Aguilar-Bryan L. Bryan J. Annu. Rev. Physiol. 1998; 60: 667-687Crossref PubMed Scopus (483) Google Scholar). Recent studies have shown that pharmacologically significant binding of the pyridine KCO, [3H]P1075, an analog of the potent “cardiovascular” KCO, pinacidil (10.Arena J.P. Kass R.S. Am. J. Physiol. 1989; 257: H2092-H2096PubMed Google Scholar), to SURs requires hydrolyzable nucleotide triphosphates, Mg2+ or Mn2+, and intact nucleotide-binding folds (both NBF1 and NBF2) (11.Dickinson K.E. Bryson C.C. Cohen R.B. Rogers L. Green D.W. Atwal K.S. Mol. Pharmacol. 1997; 52: 473-481Crossref PubMed Scopus (39) Google Scholar, 12.Hambrock A. Loffler-Walz C. Kurachi Y. Quast U. Br. J. Pharmacol. 1998; 125: 577-583Crossref PubMed Scopus (66) Google Scholar, 13.Schwanstecher M. Sieverding C. Dorschner H. Gross I. Aguilar-Bryan L. Schwanstecher C. Bryan J. EMBO J. 1998; 17: 5529-5535Crossref PubMed Scopus (199) Google Scholar). Diazoxide does not stimulate homomeric KIR6.2 channels (14.Tucker S.J. Gribble F.M. Zhao C. Trapp S. Ashcroft F.M. Nature. 1997; 387: 179-183Crossref PubMed Scopus (683) Google Scholar) and [3H]P1075 does not interact with KIR6.0 (13.Schwanstecher M. Sieverding C. Dorschner H. Gross I. Aguilar-Bryan L. Schwanstecher C. Bryan J. EMBO J. 1998; 17: 5529-5535Crossref PubMed Scopus (199) Google Scholar). The effect of diazoxide on native and reconstituted sarcolemmal channels in the presence of quasi-cytosolic [Mg-ATP] is negligible in comparison with stimulation by both cromakalim and pinacidil (1.Edwards G. Weston A.H. Annu. Rev. Pharmacol. Toxicol. 1993; 33: 597-637Crossref PubMed Scopus (529) Google Scholar, 9.Babenko A.P. Aguilar-Bryan L. Bryan J. Annu. Rev. Physiol. 1998; 60: 667-687Crossref PubMed Scopus (483) Google Scholar,15.Babenko A.P. Gonzalez G. Aguilar-Bryan L. Bryan J. Circ. Res. 1998; 83: 1132-1143Crossref PubMed Scopus (162) Google Scholar). SUR2A/KIR6.2 channels can be stimulated by diazoxide at supra-physiologic [ADP]i and submillimolar [ATP]i in the presence of Mg2+(16.D'Hahan N. Moreau C. Prost A.L. Jacquet H. Alekseev A.E. Terzic A. Vivaudou M. Proc. Natl. Acad. Sci. U. S. A. 1999; 96: 12162-12167Crossref PubMed Scopus (166) Google Scholar). This suggests diazoxide can bind to SUR2s in agreement with the stimulation of SUR2B/KIR6.2 channels (17.Isomoto S. Kondo C. Yamada M. Matsumoto S. Higashiguchi O. Horio Y. Matsuzawa Y. Kurachi Y. J. Biol. Chem. 1996; 271: 24321-24324Abstract Full Text Full Text PDF PubMed Scopus (500) Google Scholar) and with the displacement of [3H]P1075 from both SUR2 isoforms, differing in their final 42 amino acids, by diazoxide (13.Schwanstecher M. Sieverding C. Dorschner H. Gross I. Aguilar-Bryan L. Schwanstecher C. Bryan J. EMBO J. 1998; 17: 5529-5535Crossref PubMed Scopus (199) Google Scholar). By exchanging segments between SUR1 and SUR2A, D'Hahan et al.(18.D'Hahan N. Jacquet H. Moreau C. Catty P. Vivaudou M. Mol. Pharmacol. 1999; 56: 308-315Crossref PubMed Scopus (66) Google Scholar) have shown the importance of the C-terminal set of transmembrane domains of SUR2 for stimulation of K ATP channels by SR47063, a cromakalim analog. Uhde et al. (19.Uhde I. Toman A. Gross I. Schwanstecher C. Schwanstecher M. J. Biol. Chem. 1999; 274: 28079-28082Abstract Full Text Full Text PDF PubMed Scopus (111) Google Scholar) were able to identify two smaller sequences within this region critical for [3H]P1075 binding and stimulation. We have used matched human SUR1-SUR2A chimeras, previously employed to define the segments critical for SUR isoform-specific ATP-inhibitory gating (20.Babenko A.P. Gonzalez G. Bryan J. J. Biol. Chem. 1999; 274: 11587-11592Abstract Full Text Full Text PDF PubMed Scopus (66) Google Scholar) and high-affinity tolbutamide inhibition (21.Babenko A.P. Gonzalez G. Bryan J. FEBS Lett. 1999; 459: 367-376Crossref PubMed Scopus (55) Google Scholar), to validate the requirement of TMD12–17 of SUR2 for stimulation by cromakalim or pinacidil and to demonstrate that TMD6–11 and NBF1 control the responsiveness to diazoxide in the presence of Mg-ATP. The human SUR1, SUR2A, and KIR6.2 cDNAs have been described previously (22.Aguilar-Bryan L. Clement J.P., IV Gonzalez G. Kunjilwar K. Babenko A. Bryan J. Physiol. Rev. 1998; 78: 227-245Crossref PubMed Scopus (517) Google Scholar), as have the cDNAs encoding chimeric SUR I through VI, IX through XIV (20.Babenko A.P. Gonzalez G. Bryan J. J. Biol. Chem. 1999; 274: 11587-11592Abstract Full Text Full Text PDF PubMed Scopus (66) Google Scholar), and XVII (21.Babenko A.P. Gonzalez G. Bryan J. FEBS Lett. 1999; 459: 367-376Crossref PubMed Scopus (55) Google Scholar) (see Fig. 1,left panel). These chimeras were constructed initially to allow swapping of seven major domains of SUR using existing restriction sites in human SUR1 and SUR2A and, when missing, by engineering matching restriction sites. The new chimeras, XIX through XXIV, were constructed by swapping the indicated segments (Fig. 1). The co-transfection with SUR and KIR6.2 and the cultivation of COSm6 cells was done as described (15.Babenko A.P. Gonzalez G. Aguilar-Bryan L. Bryan J. Circ. Res. 1998; 83: 1132-1143Crossref PubMed Scopus (162) Google Scholar). Recording of currents from inside-out patches was done at 22–24 °C as described previously (15.Babenko A.P. Gonzalez G. Aguilar-Bryan L. Bryan J. Circ. Res. 1998; 83: 1132-1143Crossref PubMed Scopus (162) Google Scholar) using an Axopatch 200B amplifier (Axon Instruments, Inc., Foster City, CA) at a holding potential of −40 mV. Pipettes were filled up with the K+-rich external solution containing (in mm) 145 KCl, 1 MgCl2, 1 CaCl2, 10 HEPES, pH 7.4 (KOH). The Mg2+-free internal solution was (in mm) 140 KCl, 5 EDTA, 5 HEPES, 10 KOH, pH 7.2 (KOH), whereas the Mg2+-containing “intracellular” solution was (in mm) 140 KCl, 1 MgCl2, 5 EGTA, 5 HEPES, 10 KOH, pH 7.2 (KOH). Pinacidil was from Lilly Research Laboratories, and ATP (ultra-pure, di-sodium salt) and other compounds were from Sigma. The free Mg2+ concentration in all Mg2+-containing internal solutions was maintained at a quasi-cytosolic level of ∼0.7 mm, as described previously (15.Babenko A.P. Gonzalez G. Aguilar-Bryan L. Bryan J. Circ. Res. 1998; 83: 1132-1143Crossref PubMed Scopus (162) Google Scholar). Tolbutamide (200 mm stock solution in 0.1 N KOH) was added to the nucleotide-free internal solution to a final concentration of 200 μm. Diazoxide, cromakalim, or pinacidil (100 mm stock solutions in dimethyl sulfoxide, Me2SO) were added to the 0.1 mm ATP- and Mg2+-containing internal solution. The final concentrations were 300 μm diazoxide (0.3 volume % Me2SO), 200 μm cromakalim, or 100 μm pinacidil. Bathing solutions were applied using a programmable rapid solution changer (RSC-200, Biologic Inc, Claix, France). The relative NPo, used as a measure of channel activity in the presence of a test compound, was estimated as described previously (15.Babenko A.P. Gonzalez G. Aguilar-Bryan L. Bryan J. Circ. Res. 1998; 83: 1132-1143Crossref PubMed Scopus (162) Google Scholar) after applying corrections for run-down and for reactivation by Mg-ATP. Addition of 0.3 volume % Me2SO to the ∼0.1 mm Mg-ATP containing internal solution induced a small, 1.25 ± 0.26- and 1.27 ± 0.28-fold, increase in the NPo values of β-cell and cardiacK ATP channels, respectively (mean ± S.D.). The latter estimate was used to define the lower limit for a significant increase in the averaged NPo values, expressed as mean ± S.D., in the presence of either KCO (see Fig. 1). The differences in NPo values with p < 0.05 (unpaired Student'st test) were considered significant. In agreement with our original demonstration (8.Inagaki N. Gonoi T. Clement J.P., IV Wang C.Z. Aguilar-Bryan L. Bryan J. Seino S. Neuron. 1996; 16: 1011-1017Abstract Full Text Full Text PDF PubMed Scopus (880) Google Scholar), the SUR1/KIR6.2 and SUR2A/KIR6.2 channels display differences in sulfonylurea sensitivity and in responsiveness to diazoxide and cromakalim (Fig. 1). The SUR1/KIR6.2 channel currents, activated upon excision of an inside-out patch into nucleotide-free internal solution, are inhibited by ∼60% by 200 μm tolbutamide, a concentration which saturates the high-affinity binding site (21.Babenko A.P. Gonzalez G. Bryan J. FEBS Lett. 1999; 459: 367-376Crossref PubMed Scopus (55) Google Scholar), whereas the SUR2A/KIR6.2 channels are inhibited by ∼15% (15.Babenko A.P. Gonzalez G. Aguilar-Bryan L. Bryan J. Circ. Res. 1998; 83: 1132-1143Crossref PubMed Scopus (162) Google Scholar) as a result of low-affinity interaction(s) (21.Babenko A.P. Gonzalez G. Bryan J. FEBS Lett. 1999; 459: 367-376Crossref PubMed Scopus (55) Google Scholar). With ∼0.1 mmMg-ATP in the internal solution to ensure maximal binding of KCOs (11.Dickinson K.E. Bryson C.C. Cohen R.B. Rogers L. Green D.W. Atwal K.S. Mol. Pharmacol. 1997; 52: 473-481Crossref PubMed Scopus (39) Google Scholar, 12.Hambrock A. Loffler-Walz C. Kurachi Y. Quast U. Br. J. Pharmacol. 1998; 125: 577-583Crossref PubMed Scopus (66) Google Scholar, 13.Schwanstecher M. Sieverding C. Dorschner H. Gross I. Aguilar-Bryan L. Schwanstecher C. Bryan J. EMBO J. 1998; 17: 5529-5535Crossref PubMed Scopus (199) Google Scholar) and pre-inhibit channel activity, a supra-pharmacological concentration of diazoxide, 300 μm, sufficient to half-maximally saturate SUR1 and SUR2 (13.Schwanstecher M. Sieverding C. Dorschner H. Gross I. Aguilar-Bryan L. Schwanstecher C. Bryan J. EMBO J. 1998; 17: 5529-5535Crossref PubMed Scopus (199) Google Scholar), significantly attenuated nucleotide-inhibition of SUR1/KIR6.2, but not SUR2A/KIR6.2, channels. A concentration of cromakalim, sufficient to saturate SUR2A, almost completely antagonized the inhibition of SUR2A/KIR6.2 channels by 0.1 mmATP but did not stimulate SUR1/KIR6.2 channels. In the absence of either, or both, nucleotides and Mg2+(∼10−9m free Mg2+ in the Mg2+-free internal solution), stimulation by diazoxide was undetectable and stimulation by cromakalim or pinacidil was reduced ∼10-fold (not shown). The remaining nonphysiologic effect of cromakalim in the absence of Mg-ATP was not examined further. Comparison of the stimulation of chimeric SUR/KIR6.2 channels by diazoxide and cromakalim demonstrated all four possible types of channels including those differentially responsive to the two compounds, those that failed to respond to either drug and those that responded to both drugs. Analysis of six pairs of matched chimeric SURs (Fig. 1, underlined) suggested that stimulation by cromakalim was determined by the presence of TMD12–17 from SUR2 in the chimeric receptor (chimeras V through XII), whereas matched channels lacking this segment were not stimulated by cromakalim. Stimulation by diazoxide was correlated with the presence of either NBF1 and TMD6–11 from SUR1 (chimeras I through III and XII through XIV, and XI, respectively). Chimeras II and XII, containing both NBF1 and TMD6–11 of SUR1 conferred the maximal response to diazoxide, whereas chimera XI, containing TMD6–11 of SUR1 and NBF1 of SUR2, specified a lower efficacy response. Analysis of three additional pairs of chimeras with reciprocally exchanged single segments reinforces the conclusion that TMD12–17 of SUR2 confers a selective interaction with either cromakalim or pinacidil, whereas TMD6–11 and NBF1 of SUR1 contribute additively to diazoxide responsiveness. Substitution of TMD6–11 and NBF1 of SUR1 into SUR2A (chimera XXIV) was essential for maximal response to diazoxide. The separable nature of the segments that specify the selective responses of K ATP channel isoforms to the two KCOs is demonstrated by the generation of channels that are stimulated by both the “β-cell specific” and “cardiovascular” KCOs (chimeras XII, XIX through XXI, and XXIV) versus those that are not stimulated by either KCO (chimera IV and chimera XVII). The inhibition (∼60%) of these KCO-insensitive currents by 200 μm tolbutamide ensured that TMD12–17 was functionally coupled to KIR6.2 (21.Babenko A.P. Gonzalez G. Bryan J. FEBS Lett. 1999; 459: 367-376Crossref PubMed Scopus (55) Google Scholar). A direct comparison of currents through the channels responding to both types KCOs suggests a slower off-rate for the benzothiadiazine or pyridine The that two regions in SURs are to the selective of diazoxide or pinacidil. We that of SUR2, from the NBF1 through the intracellular segment in sensitivity to the benzopyran and pyridine whereas TMD6–11 and NBF1 of SUR1 specify a β-cell response to the KCO, diazoxide. demonstration that TMD12–17 of SUR2 is for cromakalim stimulation of human K ATP channels the of D'Hahan et al. N. Jacquet H. Moreau C. Catty P. Vivaudou M. Mol. Pharmacol. 1999; 56: 308-315Crossref PubMed Scopus (66) Google Scholar) that of TMD12–17 from SUR2A into SUR1 is sufficient for of chimeric SUR/KIR6.2 channels and the by Uhde et al. (19.Uhde I. Toman A. Gross I. Schwanstecher C. Schwanstecher M. J. Biol. Chem. 1999; 274: 28079-28082Abstract Full Text Full Text PDF PubMed Scopus (111) Google Scholar) that smaller and of SUR2 binding of [3H]P1075, by pinacidil and when in a SUR1 These but not that TMD12–17 is essential to a KCO binding D'Hahan et al. N. Jacquet H. Moreau C. Catty P. Vivaudou M. Mol. Pharmacol. 1999; 56: 308-315Crossref PubMed Scopus (66) Google Scholar) used a of chimeras and were to a region critical for the selective of diazoxide, Uhde et al. (19.Uhde I. Toman A. Gross I. Schwanstecher C. Schwanstecher M. J. Biol. Chem. 1999; 274: 28079-28082Abstract Full Text Full Text PDF PubMed Scopus (111) Google Scholar) TMD12–17 was sufficient to the response to KCOs and did not the of diazoxide. a matched set of SUR chimeras, the of diazoxide requires The demonstration that stimulation by diazoxide domains of SUR1 other TMD12–17 suggests these domains either diazoxide binding at TMD12–17, or at to the KIR6.2 gating or an additional with a coupling diazoxide can [3H]P1075 from and from SUR1, values for both SUR1 and SUR2 isoforms (13.Schwanstecher M. Sieverding C. Dorschner H. Gross I. Aguilar-Bryan L. Schwanstecher C. Bryan J. EMBO J. 1998; 17: 5529-5535Crossref PubMed Scopus (199) Google Scholar) and can stimulate ATP channel isoforms N. Moreau C. Prost A.L. Jacquet H. Alekseev A.E. Terzic A. Vivaudou M. Proc. Natl. Acad. Sci. U. S. A. 1999; 96: 12162-12167Crossref PubMed Scopus (166) Google Scholar, S. Kondo C. Yamada M. Matsumoto S. Higashiguchi O. Horio Y. Matsuzawa Y. Kurachi Y. J. Biol. Chem. 1996; 271: 24321-24324Abstract Full Text Full Text PDF PubMed Scopus (500) Google Scholar). The are with a model in which of including diazoxide, the site in TMD12–17 and that this in SUR1, is in to sulfonylurea binding (19.Uhde I. Toman A. Gross I. Schwanstecher C. Schwanstecher M. J. Biol. Chem. 1999; 274: 28079-28082Abstract Full Text Full Text PDF PubMed Scopus (111) Google Scholar, A.P. Gonzalez G. Bryan J. FEBS Lett. 1999; 459: 367-376Crossref PubMed Scopus (55) Google Scholar, Gribble F.M. Ashcroft S.J. Ashcroft F.M. 1999; PubMed Scopus Google Scholar). The of these sites the potential for We that regions of SUR contribute to coupling with the In SUR1/KIR6.2 channels, coupling of diazoxide binding requires TMD6–11 and NBF1, whereas the is in SUR2B/KIR6.2 channels. The of NBF1 in stimulation by diazoxide suggests nucleotide binding contribute to the efficacy of this This be with diazoxide stimulation of SUR2A/KIR6.2 channels which saturate binding N. Moreau C. Prost A.L. Jacquet H. Alekseev A.E. Terzic A. Vivaudou M. Proc. Natl. Acad. Sci. U. S. A. 1999; 96: 12162-12167Crossref PubMed Scopus (166) Google Scholar) and with isoform differences in the sequences of NBF1 and are to K. J. M. Seino S. T. Proc. Natl. Acad. Sci. U. S. A. 1999; 96: PubMed Scopus Google Scholar), and have stimulation of β-cell K ATP channels by the P. on four of that the TMD12–17 segment of a structurally transport is for J. Biol. Chem. 1999; 274: Full Text Full Text PDF PubMed Scopus Google Scholar), are to the ATPase activity of transport hydrolyzable Mg-ATP is for KCO and K ATP channel stimulation is by in the that KCOs increase an ATPase activity of SUR on of SUR K. J. M. Seino S. T. Proc. Natl. Acad. Sci. U. S. A. 1999; 96: PubMed Scopus Google Scholar). this the requirement of Mg-ATP for KCO binding an ATP and suggests KCOs be This suggests that drug binding to TMD12–17 and binding K. J. M. Seino S. T. Proc. Natl. Acad. Sci. U. S. A. 1999; 96: PubMed Scopus Google Scholar) of ATP and to NBF1 and respectively, other This the requirement for Mg-ATP and intact for KCO binding (13.Schwanstecher M. Sieverding C. Dorschner H. Gross I. Aguilar-Bryan L. Schwanstecher C. Bryan J. EMBO J. 1998; 17: 5529-5535Crossref PubMed Scopus (199) Google Scholar), of this binding by A. Loffler-Walz C. D. U. Horio Y. Kurachi Y. Quast U. Mol. Pharmacol. 1999; Google Scholar), and of the of nucleotides (21.Babenko A.P. Gonzalez G. Bryan J. FEBS Lett. 1999; 459: 367-376Crossref PubMed Scopus (55) Google Scholar), and the of from SUR1 by sulfonylureas K. J. M. Seino S. T. Proc. Natl. Acad. Sci. U. S. A. 1999; 96: PubMed Scopus Google Scholar) in Fig. Fig. a model data on the functional topology of In to sequences in and the that specify differences and ofK ATP channel isoforms (20.Babenko A.P. Gonzalez G. Bryan J. J. Biol. Chem. 1999; 274: 11587-11592Abstract Full Text Full Text PDF PubMed Scopus (66) Google Scholar), from four N. Jacquet H. Moreau C. Catty P. Vivaudou M. Mol. Pharmacol. 1999; 56: 308-315Crossref PubMed Scopus (66) Google Scholar, I. Toman A. Gross I. Schwanstecher C. Schwanstecher M. J. Biol. Chem. 1999; 274: 28079-28082Abstract Full Text Full Text PDF PubMed Scopus (111) Google Scholar, A.P. Gonzalez G. Bryan J. FEBS Lett. 1999; 459: 367-376Crossref PubMed Scopus (55) Google Scholar, Gribble F.M. Ashcroft S.J. Ashcroft F.M. 1999; PubMed Scopus Google Scholar) demonstrate that TMD12–17 is critical for the of both sulfonylureas and this region the binding for these of TMD12–17 of SUR1 intracellular in high-affinity sulfonylurea binding (19.Uhde I. Toman A. Gross I. Schwanstecher C. Schwanstecher M. J. Biol. Chem. 1999; 274: 28079-28082Abstract Full Text Full Text PDF PubMed Scopus (111) Google Scholar, A.P. Gonzalez G. Bryan J. FEBS Lett. 1999; 459: 367-376Crossref PubMed Scopus (55) Google Scholar, Gribble F.M. Ashcroft S.J. Ashcroft F.M. 1999; PubMed Scopus Google Scholar). The regions in SUR2 sequences for high-affinity binding of of domains to coupling the of binding to of the channel the of of these be in of drug binding sites. Recent studies (13.Schwanstecher M. Sieverding C. Dorschner H. Gross I. Aguilar-Bryan L. Schwanstecher C. Bryan J. EMBO J. 1998; 17: 5529-5535Crossref PubMed Scopus (199) Google Scholar, S.J. Gribble F.M. Zhao C. Trapp S. Ashcroft F.M. Nature. 1997; 387: 179-183Crossref PubMed Scopus (683) Google Scholar) have on direct for a nucleotide binding The relative currents in the presence of ∼0.1 mm Mg-ATP and 200 μm cromakalim (see Ref. N. Jacquet H. Moreau C. Catty P. Vivaudou M. Mol. Pharmacol. 1999; 56: 308-315Crossref PubMed Scopus (66) Google Scholar) are KCOs SUR from KIR6.2 and the ability of SUR to increase the sensitivity of KIR6.0 to by the of versus homomeric channels (14.Tucker S.J. Gribble F.M. Zhao C. Trapp S. Ashcroft F.M. Nature. 1997; 387: 179-183Crossref PubMed Scopus (683) Google Scholar, A.P. Gonzalez G. Aguilar-Bryan L. Bryan J. FEBS Lett. 1999; PubMed Scopus Google Scholar, P. L. Wang J. Proc. Natl. Acad. Sci. U. S. A. 1998; PubMed Scopus Google Scholar). The data that KCOs have a the and in induced by SUR2A and SUR1, respectively (20.Babenko A.P. Gonzalez G. Bryan J. J. Biol. Chem. 1999; 274: 11587-11592Abstract Full Text Full Text PDF PubMed Scopus (66) Google Scholar, A.P. Gonzalez G. Aguilar-Bryan L. Bryan J. FEBS Lett. 1999; PubMed Scopus Google Scholar). We that is no requirement for a in the of the ATP-inhibitory site on KIR6.0 or for of ATP for KCOs to open K that the first of the N of KIR6.2 high-affinity but not to SUR1 with (21.Babenko A.P. Gonzalez G. Bryan J. FEBS Lett. 1999; 459: 367-376Crossref PubMed Scopus (55) Google Scholar) are at two through which SURs can with the KIR6.0 pore We for with and