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Real J, Miranda C, Olofsson CS, Smith PA. Lipophilicity predicts the ability of nonsulphonylurea drugs to block pancreatic beta-cell K ATP channels and stimulate insulin secretion; statins as a test case. Endocrinol Diabetes Metab 2018; 1:e00017. [PMID: 30815553 PMCID: PMC6354820 DOI: 10.1002/edm2.17] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2018] [Revised: 01/18/2018] [Accepted: 02/18/2018] [Indexed: 12/26/2022] Open
Abstract
AIMS KATP ion channels play a key role in glucose-stimulated insulin secretion. However, many drugs block KATP as "off targets" leading to hyperinsulinaemia and hypoglycaemia. As such drugs are often lipophilic, the aim was to examine the relationship between drug lipophilicity (P) and IC 50 for KATP block and explore if the IC 50's of statins could be predicted from their lipophilicity and whether this would allow one to forecast their acute action on insulin secretion. MATERIALS AND METHODS A meta-analysis of 26 lipophilic, nonsulphonylurea, blockers of KATP was performed. From this, the IC 50's for pravastatin and simvastatin were predicted and then tested experimentally by exploring their effects on KATP channel activity via patch-clamp measurement, calcium imaging and insulin secretion in murine beta cells and islets. RESULTS Nonsulphonylurea drugs inhibited KATP channels with a Log IC 50 linearly related to their logP. Simvastatin blocked KATP with an IC 50 of 25 nmol/L, a value independent of cytosolic factors, and within the range predicted by its lipophilicity (21-690 nmol/L). 10 μmol/L pravastatin, predicted IC 50 0.2-12 mmol/L, was without effect on the KATP channel. At 10-fold therapeutic levels, 100 nmol/L simvastatin depolarized the beta-cell membrane potential and stimulated Ca2+ influx but did not affect insulin secretion; the latter could be explained by serum binding. CONCLUSIONS The logP of a drug can aid prediction for its ability to block beta-cell KATP ion channels. However, although the IC 50 for the block of KATP by simvastatin was predicted, the difference between this and therapeutic levels, as well as serum sequestration, explains why hypoglycaemia is unlikely to be observed with acute use of this statin.
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Affiliation(s)
- Joana Real
- Department of Physiology/Metabolic PhysiologyInstitute of Neuroscience and PhysiologyGöteborgSweden
| | - Caroline Miranda
- Department of Physiology/Metabolic PhysiologyInstitute of Neuroscience and PhysiologyGöteborgSweden
| | - Charlotta S. Olofsson
- Department of Physiology/Metabolic PhysiologyInstitute of Neuroscience and PhysiologyGöteborgSweden
| | - Paul A. Smith
- School of Life Sciences University of NottinghamNottinghamUK
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2
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Haythorne E, Hamilton DL, Findlay JA, Beall C, McCrimmon RJ, Ashford MLJ. Chronic exposure to K ATP channel openers results in attenuated glucose sensing in hypothalamic GT1-7 neurons. Neuropharmacology 2016; 111:212-222. [PMID: 27618741 DOI: 10.1016/j.neuropharm.2016.09.008] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2016] [Revised: 07/06/2016] [Accepted: 09/07/2016] [Indexed: 10/21/2022]
Abstract
Individuals with Type 1 diabetes (T1D) are often exposed to recurrent episodes of hypoglycaemia. This reduces hormonal and behavioural responses that normally counteract low glucose in order to maintain glucose homeostasis, with altered responsiveness of glucose sensing hypothalamic neurons implicated. Although the molecular mechanisms are unknown, pharmacological studies implicate hypothalamic ATP-sensitive potassium channel (KATP) activity, with KATP openers (KCOs) amplifying, through cell hyperpolarization, the response to hypoglycaemia. Although initial findings, using acute hypothalamic KCO delivery, in rats were promising, chronic exposure to the KCO NN414 worsened the responses to subsequent hypoglycaemic challenge. To investigate this further we used GT1-7 cells to explore how NN414 affected glucose-sensing behaviour, the metabolic response of cells to hypoglycaemia and KATP activity. GT1-7 cells exposed to 3 or 24 h NN414 exhibited an attenuated hyperpolarization to subsequent hypoglycaemic challenge or NN414, which correlated with diminished KATP activity. The reduced sensitivity to hypoglycaemia was apparent 24 h after NN414 removal, even though intrinsic KATP activity recovered. The NN414-modified glucose responsiveness was not associated with adaptations in glucose uptake, metabolism or oxidation. KATP inactivation by NN414 was prevented by the concurrent presence of tolbutamide, which maintains KATP closure. Single channel recordings indicate that NN414 alters KATP intrinsic gating inducing a stable closed or inactivated state. These data indicate that exposure of hypothalamic glucose sensing cells to chronic NN414 drives a sustained conformational change to KATP, probably by binding to SUR1, that results in loss of channel sensitivity to intrinsic metabolic factors such as MgADP and small molecule agonists.
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Affiliation(s)
- Elizabeth Haythorne
- Division of Molecular and Clinical Medicine, School of Medicine, Ninewells Hospital & Medical School, University of Dundee, Dundee, UK.
| | - D Lee Hamilton
- Division of Molecular and Clinical Medicine, School of Medicine, Ninewells Hospital & Medical School, University of Dundee, Dundee, UK.
| | - John A Findlay
- Division of Molecular and Clinical Medicine, School of Medicine, Ninewells Hospital & Medical School, University of Dundee, Dundee, UK.
| | - Craig Beall
- Division of Molecular and Clinical Medicine, School of Medicine, Ninewells Hospital & Medical School, University of Dundee, Dundee, UK.
| | - Rory J McCrimmon
- Division of Molecular and Clinical Medicine, School of Medicine, Ninewells Hospital & Medical School, University of Dundee, Dundee, UK.
| | - Michael L J Ashford
- Division of Molecular and Clinical Medicine, School of Medicine, Ninewells Hospital & Medical School, University of Dundee, Dundee, UK.
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3
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Teramoto N. Pharmacological Profile of U-37883A, a Channel Blocker of Smooth Muscle-Type ATP-Sensitive K Channels. ACTA ACUST UNITED AC 2006; 24:25-32. [PMID: 16939631 DOI: 10.1111/j.1527-3466.2006.00025.x] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
U-37883A (PNU-37883A, guanidine; 4-morpholinecarboximidine-N-1-adamantyl-N'-cyclohexyl hydrochloride) was originally developed as a potential diuretic with specific binding in kidney and vascular smooth muscle rather than in brain or pancreatic beta cells. U-37883A inhibits ATP-sensitive K(+) channels (K(ATP) channels) in vascular smooth muscle at submicromolar concentrations whilst even at high concentrations (> or =10 microM) it has no inhibitory effect at pancreatic, cardiac or skeletal K(ATP) channels. Thus, it is generally thought that U-37883A is a selective inhibitor of vascular smooth muscle K(ATP) channels. Approximately one decade ago, K(ATP) channels were cloned and found to consist of at least two subunits: an inwardly-rectifying K(+) channel six family (K(ir)6.x; K(ir)6.1 and K(ir)6.2) which forms the ion conducting pore and a modulatory sulphonylurea receptor (SUR.x; SUR1, SUR2A, and SUR2B) that accounts for several pharmacological properties. It is generally believed that different combinations of K(ir)6.x and SUR.x determine the molecular properties of K(ATP) channels. Thus, K(ir)6.2/SUR1 channel represents the pancreatic beta-cell K(ATP) channel, K(ir)6.2/SUR2A channel is thought to represent the cardiac K(ATP) channel, whereas K(ir)6.1/SUR2B channel is likely to represent the vascular smooth muscle K(ATP) channel. Recent molecular studies have shown that U-37883A selectively suppresses the activity of recombinant K(ATP) channels which contain K(ir)6.1 subunits in the channel pore unit. It was thus thought that U-37883A was a selective pharmacological tool which could be used to investigate the activity of vascular smooth muscle K(ATP) channels. However, due to its multiple pharmacological actions on several ion channels and poor tissue selectivity, U-37883A should not be viewed as a selective blocker of smooth muscle K(ATP) channels.
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Affiliation(s)
- Noriyoshi Teramoto
- Department of Pharmacology, Graduate School of Medical Sciences, Kyushu University, Japan.
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4
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McKay NG, Kinsella JM, Campbell CM, Ashford ML. Sensitivity of Kir6.2-SUR1 currents, in the absence and presence of sodium azide, to the K(ATP) channel inhibitors, ciclazindol and englitazone. Br J Pharmacol 2000; 130:857-66. [PMID: 10864893 PMCID: PMC1572145 DOI: 10.1038/sj.bjp.0703395] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Two electrode voltage clamp and single channel recordings were used to investigate the actions of various ATP-sensitive K(+) (K(ATP)) channel inhibitors on cloned K(ATP) channels, expressed in Xenopus oocytes and HEK 293 cells. Oocytes expressing Kir6.2 and SUR1 gave rise to inwardly rectifying K(+) currents following bath application of 3 mM sodium azide. Inside-out recordings from non-azide treated oocytes demonstrated the presence of K(ATP) channels which were activated by direct application of 3 mM azide and 0.1 mM Mg-ATP. Tolbutamide inhibited azide-induced macroscopic Kir6.2-SUR1 currents, recorded from Xenopus oocytes, with an IC(50) value similar to native K(ATP) channels. Ciclazindol and englitazone also inhibited these currents in a concentration-dependent manner, but with relative potencies substantially less than for native K(ATP) channels. Single channel currents recorded from inside-out patches excised from oocytes expressing Kir6.2-SUR1 currents were inhibited by tolbutamide, Mg-ATP, englitazone and ciclazindol, in the absence of azide, with potencies similar to native K(ATP) channels. In the presence of azide, Kir6.2-SUR1 currents were inhibited by englitazone and tolbutamide but not ciclazindol. Single channel currents derived from Kir6.2Delta26, expressed in HEK 293 cells, were inhibited by ciclazindol and englitazone irrespective of the absence or presence of SUR1. In conclusion, heterologously expressed Kir6.2 and SUR1 recapitulate the pharmacological profile of native pancreatic beta-cell K(ATP) channels. However, currents induced by azide exhibit a substantially reduced sensitivity to ciclazindol. It is likely that ciclazindol and englitazone inhibit K(ATP) currents by interaction with the Kir6.2 subunit.
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Affiliation(s)
- N G McKay
- Department of Biomedical Sciences, Institute of Medical Sciences, Foresterhill, University of Aberdeen, Aberdeen AB25 2ZD
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5
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Sakura H, Trapp S, Liss B, Ashcroft FM. Altered functional properties of KATP channel conferred by a novel splice variant of SUR1. J Physiol 1999; 521 Pt 2:337-50. [PMID: 10581306 PMCID: PMC2269677 DOI: 10.1111/j.1469-7793.1999.00337.x] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
Abstract
1. ATP-sensitive potassium (KATP) channels are composed of pore-forming (Kir6.x) and regulatory sulphonylurea receptor (SURx) subunits. We have isolated a novel SUR variant (SUR1bDelta33) from a hypothalamic cDNA library. This variant lacked exon 33 and introduced a frameshift that produced a truncated protein lacking the second nucleotide binding domain (NBD2). It was expressed at low levels in hypothalamus, midbrain, heart and the insulin-secreting beta-cell line MIN6. 2. We examined the properties of KATP channels composed of Kir6.2 and SUR1bDelta33 by recording macroscopic currents in membrane patches excised from Xenopus oocytes expressing these subunits. We also investigated the effect of truncating SUR1 at either the start (SUR1bT1) or end (SUR1bT2) of exon 33 on KATP channel properties. 3. Kir6.2/SUR1bDelta33 showed an enhanced open probability (Po = 0.6 at -60 mV) and a reduced ATP sensitivity (Ki, 86 microM), when compared with wild-type channels (Po = 0.3; Ki, 22 microM). However, Kir6.2/SUR1bT1 and Kir6.2/SUR1bT2 resembled the wild-type channel in their Po and ATP sensitivity. 4. Neither MgADP, nor the K+ channel opener diazoxide, enhanced Kir6.2/SUR1bDelta33, Kir6.2/SUR1bT1 or Kir6.2/SUR1bT2 currents, consistent with the idea that these agents require an intact NBD2 for their action. Sulphonylureas blocked KATP channels containing any of the three SUR variants, but in excised patches the extent of block was less than that for the wild-type channel. In intact cells, the extent of sulphonylurea block of Kir6.2/SUR1bDelta33 was greater than that in excised patches and was comparable to that found for wild-type channels. 5. Our results demonstrate that NBD2 is not essential for functional expression or sulphonylurea block, but is required for KATP channel activation by K+ channel openers and nucleotides. Some of the unusual properties of Kir6.2/SUR1bDelta33 resemble those reported for the KATP channel of ventromedial hypothalamic (VMH) neurones, but the fact that this mRNA is expressed at low levels in many other tissues makes it less likely that SUR1bDelta33 serves as the SUR subunit for the VMH KATP channel.
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Affiliation(s)
- H Sakura
- University Laboratory of Physiology, Parks Road, Oxford OX1 3PT, UK
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Lee K, Dixon AK, Richardson PJ, Pinnock RD. Glucose-receptive neurones in the rat ventromedial hypothalamus express KATP channels composed of Kir6.1 and SUR1 subunits. J Physiol 1999; 515 ( Pt 2):439-52. [PMID: 10050011 PMCID: PMC2269154 DOI: 10.1111/j.1469-7793.1999.439ac.x] [Citation(s) in RCA: 83] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
Abstract
1. Patch-clamp recordings were made from rat ventromedial hypothalamic neurones in slices of brain tissue in vitro. In cell-attached recordings, removal of extracellular glucose or metabolic inhibition with sodium azide reduced the firing rate of a subpopulation of cells through the activation of a 65 pS channel that was blocked by the sulphonylureas tolbutamide and glibenclamide. 2. In whole-cell patch-clamp recordings, in the absence of ATP in the electrode solution, glucose-receptive neurones gradually hyperpolarized due to the induction of an outward current at -60 mV. This outward current and the resultant hyperpolarization were blocked by the sulphonylureas tolbutamide and glibenclamide. 3. In recordings where the electrode solution contained 4 mM ATP, this outward current was not observed. Under these conditions, 500 microM diazoxide was found to induce an outward current that was blocked by tolbutamide. 4. In cell-attached recordings diazoxide and the active fragment of leptin (leptin 22-56) reduced the firing rate of glucose-receptive neurones by the activation of a channel with similar properties to that induced by removal of extracellular glucose. 5. Reverse transcription followed by the polymerase chain reaction using cytoplasm from single glucose-receptive neurones demonstrated the expression of the ATP-sensitive potassium (KATP) channel subunits Kir6.1 and SUR1 but not Kir6.2 or SUR2. 6. It is concluded that glucose-receptive neurones within the rat ventromedial hypothalamus exhibit a KATP channel current with pharmacological and molecular properties similar to those reported in other tissues.
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Affiliation(s)
- K Lee
- Parke Davis Neuroscience Research Centre, Cambridge University Forvie Site, Cambridge CB2 2QB, UK.
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7
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Harvey J, Ashford ML. Diazoxide- and leptin-activated K(ATP) currents exhibit differential sensitivity to englitazone and ciclazindol in the rat CRI-G1 insulin-secreting cell line. Br J Pharmacol 1998; 124:1557-65. [PMID: 9723971 PMCID: PMC1565548 DOI: 10.1038/sj.bjp.0702000] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
1. The effects of the antidiabetic agent englitazone and the anorectic drug ciclazindol on ATP-sensitive K+ (K(ATP)) channels activated by diazoxide and leptin were examined in the CRI-G1 insulin-secreting cell line using whole cell and single channel recording techniques. 2. In whole cell current clamp mode, the hyperglycaemic agent diazoxide (200 microM) and the ob gene product leptin (10 nM) hyperpolarised CRI-G1 cells by activation of K(ATP) currents. K(ATP) currents activated by either agent were inhibited by tolbutamide, with an IC50 for leptin-activated currents of 9.0 microM. 3. Application of englitazone produced a concentration-dependent inhibition of K(ATP) currents activated by diazoxide (200 microM) with an IC50 value of 7.7 microM and a Hill coefficient of 0.87. In inside-out patches englitazone (30 microM) also inhibited K(ATP) channel currents activated by diazoxide by 90.8+/-4.1%. 4. In contrast, englitazone (1-30 microM) failed to inhibit K(ATP) channels activated by leptin, although higher concentrations (> 30 microM) did inhibit leptin actions. The englitazone concentration inhibition curve in the presence of leptin resulted in an IC50 value and Hill coefficient of 52 microM and 3.2, respectively. Similarly, in inside-out patches englitazone (30 microM) failed to inhibit the activity of K(ATP) channels in the presence of leptin. 5. Ciclazindol also inhibited K(ATP) currents activated by diazoxide (200 microM) in a concentration-dependent manner, with an IC50 and Hill coefficient of 127 nM and 0.33, respectively. Furthermore, application of ciclazindol (1 microM) to the intracellular surface of inside-out patches inhibited K(ATP) channel currents activated by diazoxide (200 microM) by 86.6+/-8.1%. 6. However, ciclazindol was much less effective at inhibiting KATP currents activated by leptin (10 nM). Ciclazindol (0.1-10 microM) had no effect on K(ATP) currents activated by leptin, whereas higher concentrations (> 10 microM) did cause inhibition with an IC50 value of 40 microM and an associated Hill coefficient of 2.7. Similarly, ciclazindol (1 microM) had no significant effect on K(ATP) channel activity following leptin addition in excised inside-out patches. 7. In conclusion, K(ATP) currents activated by diazoxide and leptin show different sensitivity to englitazone and ciclazindol. This may be due to differences in the mechanism of activation of K(ATP) channels by diazoxide and leptin.
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Affiliation(s)
- J Harvey
- Department of Biomedical Sciences, Institute of Medical Sciences, University of Aberdeen, Foresterhill
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8
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Lee K, Dixon AK, Freeman TC, Richardson PJ. Identification of an ATP-sensitive potassium channel current in rat striatal cholinergic interneurones. J Physiol 1998; 510 ( Pt 2):441-53. [PMID: 9705995 PMCID: PMC2231058 DOI: 10.1111/j.1469-7793.1998.441bk.x] [Citation(s) in RCA: 62] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
Abstract
1. Whole-cell patch-clamp recordings were made from rat striatal cholinergic interneurones in slices of brain tissue in vitro. In the absence of ATP in the electrode solution, these neurones were found to gradually hyperpolarize through the induction of an outward current at -60 mV. This outward current and the resultant hyperpolarization were blocked by the sulphonylureas tolbutamide and glibenclamide and by the photorelease of caged ATP within neurones. 2. This ATP-sensitive outward current was not observed when 2 mM ATP was present in the electrode solution. Under these conditions, 500 microM diazoxide was found to induce an outward current that was blocked by tolbutamide. 3. Using permeabilized patch recordings, neurones were shown to hyperpolarize in response to glucose deprivation or metabolic poisoning with sodium azide (NaN3). The resultant hyperpolarization was blocked by tolbutamide. 4. In cell-attached recordings, metabolic inhibition with 1 mM NaN3 revealed the presence of a tolbutamide-sensitive channel exhibiting a unitary conductance of 44.1 pS. 5. Reverse transcription followed by the polymerase chain reaction using cytoplasm from single cholinergic interneurones demonstrated the expression of the ATP-sensitive potassium (KATP) channel subunits Kir6.1 and SUR1 but not Kir6.2 or SUR2. 6. It is concluded that cholinergic interneurones within the rat striatum exhibit a KATP channel current and that this channel is formed from Kir6.1 and SUR1 subunits.
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Affiliation(s)
- K Lee
- Parke Davis Neuroscience Research Centre, Cambridge University Forvie Site, UK.
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9
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Herson PS, Dulock KA, Ashford ML. Characterization of a nicotinamide-adenine dinucleotide-dependent cation channel in the CRI-G1 rat insulinoma cell line. J Physiol 1997; 505 ( Pt 1):65-76. [PMID: 9409472 PMCID: PMC1160094 DOI: 10.1111/j.1469-7793.1997.065bc.x] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
1. Cell-free excised membrane patches were used to examine the properties of a novel nicotinamide-adenine dinucleotide (beta-NAD+)-activated ion channel in the rat insulin-secreting cell line, CRI-G1. 2. In inside-out recordings, beta-NAD+ (0.05-1.0 mM) induced the appearance of a channel characterized by extremely slow kinetics, with mean open times in the range of seconds. The estimated EC50 for activation was 114 microM. Channel activity declined with time (run-down) following activation by beta-NAD+ in excised patches and this was not prevented by intracellular application of trypsin. 3. The single channel current-voltage relationship was linear with a conductance of 74 pS in symmetrical NaCl. The channel appears equally permeable to Na+, K+ and Cs+, exhibits an appreciable permeability to Ca2+, Mg2+ and Ba2+, but excludes anions. 4. The channel displays an unusual voltage sensitivity, with an abrupt increase in open-state probability at depolarized voltages. 5. Channel opening, in the presence of beta-NAD+, required both Ca2+ and Mg2+ to be present at the internal side of the membrane. Activation by Ca2+ required a concentration of at least 10 microM and was maximal at 0.1 mM. Ba2+ did not substitute for Ca2+ in inducing channel activity nor did it inhibit activation by Ca2+. Increasing the concentration of intracellular Mg2+ stabilized the open state of NAD(+)-activated channels. 6. The non-selective cation channel reported here differs in its gating and modulatory characteristics from non-selective cation channels described in other tissues. This channel may play a role in the pathophysiological responses of beta-cells to oxidative stress.
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Affiliation(s)
- P S Herson
- Department of Biomedical Sciences, University of Aberdeen, Foresterhill, UK
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10
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Lee K, McKenna F, Rowe IC, Ashford ML. The effects of neuroleptic and tricyclic compounds on BKCa channel activity in rat isolated cortical neurones. Br J Pharmacol 1997; 121:1810-6. [PMID: 9283722 PMCID: PMC1564885 DOI: 10.1038/sj.bjp.0701333] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
1. The actions of several neuroleptic and tricyclic compounds were examined on the large conductance Ca(2+)-activated K+ (BKCa) channel present in neurones isolated from the rat motor cortex. 2. Classical neuroleptic compounds including chlorpromazine and haloperidol applied to the intracellular surface of inside-out patches produced a concentration-dependent reduction in BKCa channel activity. Similar effects were observed when these compounds were applied to the extracellular surface of outside-out patches. 3. In contrast, the atypical neuroleptic compounds clozapine and sulpiride did not affect BKCa channel activity (100 nM-1 mM) in either inside-out or outside-out patches, while 10 microM pimozide produced 73% of the inhibition produced by 10 microM chlorpromazine. 4. BKCa channel activity was also unaffected by application of structurally related tricyclic compounds including the anti-cholinesterase tacrine and the anti-epileptic carbamazepine. The tricyclic antidepressant drug amitriptyline was found to inhibit BKCa channel activity but was much less effective than the classical neuroleptic compounds. 5. It is concluded that compounds belonging to the classical neuroleptic group of drugs inhibit BKCa channel activity in the rat motor cortex in a structurally-specific manner. This observation may be of clinical significance as it may contribute to some of the side effects associated with classical neuroleptic drug therapy.
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Affiliation(s)
- K Lee
- Department of Biomedical Sciences, University of Aberdeen, Foresterhill
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11
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Rowe IC, Lee K, Khan RN, Ashford ML. Effect of englitazone on KATP and calcium-activated non-selective cation channels in CRI-G1 insulin-secreting cells. Br J Pharmacol 1997; 121:531-9. [PMID: 9179397 PMCID: PMC1564701 DOI: 10.1038/sj.bjp.0701145] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
1. The effects of englitazone sodium, an antidiabetic agent, on ion channel activity in the CRI-G1 insulin secreting cell line was examined by use of the patch clamp technique. 2. Application of englitazone to the outside of CRI-G1 cells in the whole-cell recording configuration produced concentration-dependent inhibition of KATP currents with an IC50 value of 8 microM. The inhibition of the K+ current was not affected by the removal of Mg2+ ions from or the addition of trypsin to the solution bathing the intracellular surface of the cell membrane. 3. Englitazone also inhibited KATP channel activity in recordings from inside out excise membrane patches. The concentration-dependence of inhibition was identical to that observed in whole-cell recordings and was voltage-independent. Single channel recordings confirmed that neither the absence or presence of Mg2+ ions nor the addition of trypsin at the intracellular surface of the membrane influenced the inhibition of KATP channels by englitazone. 4. Englitazone also inhibited Ca(2+)-activated non-selective cation (NSCa) channels in inside-out patches in a concentration-dependent and voltage-independent manner with an IC50 value of 10 microM. In comparison, the non-sulphonylurea KATP channel blocker ciclazindol produced a slight voltage-dependent inhibition of the NSCa channel at a concentration of 20 microM. 5. In whole-cell recordings englitazone, at a relatively high concentration (50 microM) in comparison with that required to block KATP and NSCa channels, inhibited voltage-activated Ca2+ currents by 33% but did not inhibit voltage-activated K+ and Na+ currents. 6. It is concluded that englitazone is a novel blocker of NSCa and KATP channels. The inhibition of KATP channels occurs following procedures that dissociate sulphonylurea receptor coupling to the channel. The equipotent and voltage-independent inhibition of NSCa and KATP channels by englitazone may indicate a common mechanism of block.
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Affiliation(s)
- I C Rowe
- Department of Biomedical Sciences, Marischal College, University of Aberdeen
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12
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Lee K, Ibbotson T, Richardson PJ, Boden PR. Inhibition of KATP channel activity by troglitazone in CRI-G1 insulin-secreting cells. Eur J Pharmacol 1996; 313:163-7. [PMID: 8905344 DOI: 10.1016/0014-2999(96)00619-x] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Patch-clamp recording techniques were used to examine the effect of troglitazone on KATP channel activity in Cambridge rat insulinoma-G1 (CRI-G1) insulin-secreting cells. In both inside-out and outside-out patch recordings, bath application of troglitazone reduced KATP channel activity. This inhibition was independent of the membrane voltage and was poorly reversible. In whole-cell studies, troglitazone inhibited KATP channel currents with an IC50 of 697 +/- 92 nM and an associated Hill coefficient of 1.2 +/- 0.2. In current clamp recordings 10 microM troglitazone depolarised the CRI-G1 cell membrane by 36.8 +/- 3.9 mV with a concomitant decrease in membrane conductance. However, in contrast to the rapid depolarisation produced by tolbutamide, the effects of troglitazone developed more slowly, usually taking 15-20 min to develop.
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Affiliation(s)
- K Lee
- Parke Daris Neuroscience Research Centre, Cambridge University Forvie Site, UK
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13
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Zhang HL, Bolton TB. Two types of ATP-sensitive potassium channels in rat portal vein smooth muscle cells. Br J Pharmacol 1996; 118:105-14. [PMID: 8733582 PMCID: PMC1909472 DOI: 10.1111/j.1476-5381.1996.tb15372.x] [Citation(s) in RCA: 86] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
1. Single-channel recordings were made from single, enzymatically isolated smooth muscle cells of rat portal vein by the patch-clamp technique. 2. Unitary potassium currents were identified through two types of K-channels with conductances in 60:130 mM K-gradient of 50 and 22 pS; these are referred to as LK and MK channels respectively. 3. The LK channels became extremely active if isolated patches were created into nucleotide-free solution; activity was inhibited by ATP applied to the inner surface of the patch with a half maximal inhibition (Ki) of 11-23 microM. Channel activity declined and disappeared with time and could be regenerated by a brief application of Mg-ATP or a nucleoside diphosphate such as UDP (in the presence of Mg). LK channel activity was rarely stimulated by levcromakalim and not by pinacidil (K-channel openers, KCOs) but was blocked by glibenclamide. 4. Activity of MK channels declined if isolated patches were created into nucleotide free solution; activity reappeared if UDP or ATP alone (in the presence of Mg) was applied; pinacidil or levcromakalim in the presence of ATP or UDP further increased channel activity which was blocked by glibenclamide. 5. The LK channel inhibited by ATPi is very similar in its conductance and other properties to the KATP channel described in tissues other than smooth muscle, in its conductance and properties the MK channel resembles the KNDP channel we have previous described as present in other smooth muscles and opening in responses to KCOs.
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Affiliation(s)
- H L Zhang
- Department of Pharmacology and Clinical Pharmacology, St George's Hospital Medical School, London
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14
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Lee K, Dixon AK, Rowe IC, Ashford ML, Richardson PJ. Direct demonstration of sulphonylurea-sensitive KATP channels on nerve terminals of the rat motor cortex. Br J Pharmacol 1995; 115:385-7. [PMID: 7582446 PMCID: PMC1908424 DOI: 10.1111/j.1476-5381.1995.tb16344.x] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
We examined whether ATP-sensitive potassium (KATP) channels are present on presynaptic terminals of the rat motor cortex, an area of the CNS exhibiting a high density of sulphonylurea binding. A novel fused nerve terminal preparation was developed which produced structures amenable to patch clamp methods. In inside-out recordings a K+ channel was observed which possessed all the major features of the Type 1 KATP channel, including sensitivity to ATP and the antidiabetic sulphonylureas.
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Affiliation(s)
- K Lee
- Department of Pharmacology, University of Cambridge
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15
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Röper J, Ashcroft FM. Metabolic inhibition and low internal ATP activate K-ATP channels in rat dopaminergic substantia nigra neurones. Pflugers Arch 1995; 430:44-54. [PMID: 7667078 DOI: 10.1007/bf00373838] [Citation(s) in RCA: 71] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
The patch-clamp technique was used to study whole-cell currents of acutely dissociated rat substantia nigra (SN) neurones. In perforated-patch current-clamp recordings, inhibition of mitochondrial metabolism by rotenone (5 microM) produced a hyperpolarisation and inhibited electrical activity. These effects were reversed by the sulphonylureas tolbutamide (0.5 mM) or glibenclamide (0.5 microM). Under voltage-clamp conditions, rotenone induced a time- and voltage-independent K+ current which was selectively blocked by sulphonylureas. The glibenclamide-sensitive current reversed at -81.7 +/- 2.7 mV (n = 5) and showed marked inward rectification. Intracellular dialysis with 0.3 mM adenosine 5'-triphosphate (ATP), but not 2 mM or 5 mM ATP, in standard whole-cell recordings also resulted in activation of a sulphonylurea-sensitive K+ current with similar properties (reversal potential, -81.9 +/- 2.5 mV, n = 5). The close similarity in the properties of the ATP-sensitive K+ current observed in whole-cell recordings and the K+ current activated by metabolic inhibition in perforated-patch recordings suggest that they both result from activation of the same type of ATP-sensitive K+ channel. Sulphonylureas had no effect on electrical activity or membrane currents in the absence of rotenone in perforated-patch recordings, or in cells dialysed with 5 mM ATP, indicating that in SN neurones these drugs are selective for the ATP-sensitive K+ current.
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Affiliation(s)
- J Röper
- University Laboratory of Physiology, Oxford, UK
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16
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Yamashita T, Masuda Y, Shikada KI, Tanaka S. Cardiovascular Pharmacology of NIP-121, A Potassium Channel Opener. ACTA ACUST UNITED AC 1995. [DOI: 10.1111/j.1527-3466.1995.tb00215.x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
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17
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Ozanne SE, Guest PC, Hutton JC, Hales CN. Intracellular localization and molecular heterogeneity of the sulphonylurea receptor in insulin-secreting cells. Diabetologia 1995; 38:277-82. [PMID: 7758873 DOI: 10.1007/bf00400631] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Sulphonylureas stimulate insulin secretion by binding to a receptor in the pancreatic beta-cell plasma membrane resulting in inhibition of ATP-sensitive K+ channels, membrane depolarization and thus influx of Ca2+ through voltage-dependent Ca2+ channels. Sulphonylureas can also induce hormone release at fixed membrane potentials without Ca2+ entry suggesting that these drugs may have other modes of action. We have determined whether different forms of sulphonylurea-binding proteins are present in insulin-secreting cells and their subcellular localization by density gradient centrifugation. Binding studies using [3H]-glibenclamide showed that islet and insulinoma membranes contained a single high affinity sulphonylurea binding site (Kd = 1 nmol/l). Photo-crosslinking of the drug to the membranes resulted in labelling of two proteins with apparent molecular weights of 170 and 140 kDa. The same analyses of insulinoma subcellular fractions showed that the majority (> 90%) of binding proteins were localized to intracellular membranes with only minor levels (< 10%) on plasma membranes. The 170 kDa sulphonylurea binding protein was present in both plasma and granule membrane fractions whereas the 140 kDa form was not present in the plasma membrane fraction. The differences in the molecular forms and subcellular distribution of the receptor are consistent with sulphonylureas having multiple sites of action in the pancreatic beta cell.
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Affiliation(s)
- S E Ozanne
- Department of Clinical Biochemistry, University of Cambridge, Addenbrooke's Hospital, UK
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18
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Yamashita T, Masuda Y, Tanaka S. The effects of potassium channel openers and blockers on the specific binding sites for [3H]glibenclamide in rat tissues. JAPANESE JOURNAL OF PHARMACOLOGY 1995; 67:35-44. [PMID: 7745843 DOI: 10.1254/jjp.67.35] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
The effects of K+ channel openers (PCOs), NIP-121, levcromakalim and nicorandil, and the blockers of the specific binding sites for [3H]glibenclamide, ATP-sensitive K+ channel blocker, were investigated in rat brain and cardiac ventricle membrane preparations. When the microsomes were incubated with [3H]glibenclamide, the specific glibenclamide binding was fully inhibited by unlabeled glibenclamide (1 microM) and apamin (100 microM). However, the specific glibenclamide binding was not influenced by excess NIP-121, levcromakalim and nicorandil, although glibenclamide antagonized the increase in the 86Rb+ efflux by PCOs. On the other hand, the binding of [3H]glibenclamide after a long pre-incubation (60 min) at 37 degrees C with NIP-121 and levcromakalim at pharmacological effective concentrations (10 nM to 1 microM) was significantly influenced. Both PCOs partially reduced both Kd and Bmax values of the specific [3H]glibenclamide binding in a concentration-dependent manner that was not regulated by GTP gamma S. The dose-effect relationships for the Bmax's of NIP-121 and levcromakalim seemed similar to those for vasorelaxation. These findings indicate that the pharmacological effect of PCO may be caused by the binding to its own specific sites but not to the specific sulfonylurea sites. The binding of PCOs may inhibit, in a negative allosteric manner the binding of sulfonylureas.
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Affiliation(s)
- T Yamashita
- Shiraoka Research Station of Biological Science, Nissan Chemical Industries, Ltd., Saitama, Japan
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19
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Ashford ML, Bond CT, Blair TA, Adelman JP. Cloning and functional expression of a rat heart KATP channel. Nature 1994; 370:456-9. [PMID: 8047164 DOI: 10.1038/370456a0] [Citation(s) in RCA: 152] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Potassium channels that are ATP-sensitive (KATP) couple membrane potential to the metabolic status of the cell. KATP channels are inhibited by intracellular ATP and are stimulated by intracellular nucleotide diphosphates. KATP channels are important regulators of secretory processes and muscle contraction, and are targets for therapeutic treatment of type II diabetes by the inhibitory sulphonylureas and for hypertension by activators such as pinacidil. In cardiac tissue, KATP channels are central regulators of post-ischaemic cardioprotection. Electrophysiological and pharmacological characteristics vary among KATP channels recorded from diverse tissues suggesting extensive molecular heterogeneity. A complementary DNA encoding a KATP channel was isolated from rat heart using the polymerase chain reaction. We report here that the expressed channels possess all of the essential features of native cardiac KATP channels, including sensitivity to intracellular nucleotides. In addition the cloned channels are activated by the potassium channel opener, pinacidil, but are not inhibited by the sulphonylurea, glibenclamide.
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Affiliation(s)
- M L Ashford
- Department of Pharmacology, University of Cambridge, UK
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