SAR analysis for compounds that activate KCNQ1 potassium channels in the KCNQ1 expressing cells on automated patch clamp III
Voltage-gated potassium channels [1,2] are tetrameric membrane proteins that selectively conduct K+ across cellular membranes, thus open, close, and inactivate in response to changes in transmembrane voltage . Individual subtypes of these potassium channels often have a unique expression pattern allowing cells to "fine-tune" membrane potentials and excitability according to their respective more ..
BioActive Compounds: 8
Data Source: Johns Hopkins Ion Channel Center (JHICC_KCNQ1_Act_SAR_IWS_3)
BioAssay Type: Confirmatory, Concentration-Response Relationship Observed
Source (MLPCN Center Name): Johns Hopkins Ion Channel Center (JHICC)
Center Affiliation: Johns Hopkins University, School of Medicine
Screening Center PI: Min Li, Ph.D.
Assay Provider: Meng Wu, Ph.D.
Network: Molecular Libraries Probe Production Centers Network (MLPCN)
Grant Proposal Number: 1 R03 MH090837-01
Grant Proposal PI: Meng Wu, Ph.D., Johns Hopkins University School of Medicine
Assay Implementation: Haibo Yu Ph.D., Kaiping Xu M.S., Owen McManus, Ph.D., Meng Wu Ph.D.
Voltage-gated potassium channels [1,2] are tetrameric membrane proteins that selectively conduct K+ across cellular membranes, thus open, close, and inactivate in response to changes in transmembrane voltage . Individual subtypes of these potassium channels often have a unique expression pattern allowing cells to "fine-tune" membrane potentials and excitability according to their respective physiological functions . Dysfunctions of these electrical excitability controlling proteins, either congenital or acquired, are attributed to a variety of diseases [5,6], such as cardiac arrhythmias, diabetes, hypertension, and epilepsy. Specific modulation of individual potassium channel types therefore represents an enormous potential for the development of physiological tool compounds and new drugs [7-9].
KCNQ1 (Kv7.1, KvLQT) [10,11] is an alpha-subunit subtype of voltage-gated KCNQ potassium channel family, which is composed of five members of KCNQ1-KCNQ5. They share between 30% and 65% amino acid identity. A classical KCNQ alpha-subunit is composed of six transmembrane segments, including a voltage-sensor segment and a pore domain [12-15]. Unique from other members of KCNQ family , KCNQ1 has been generally absent from neuronal tissues, mainly expressed in heart, kidney, small intestine, pancreas, prostate and other non-excitable epithelial tissues. Also contrast to other members of KCNQ family which form both alpha-subunit homo- and heterotetrameric channels, KCNQ1 channels only form alpha-subunit homotetramers . They commonly co-assemble with beta-subunit KCNE proteins to give rise to functional variations in different tissues.
These molecular assemblies have afforded KCNQ1 with two important physiological functions: 1) repolarization of the cardiac tissue following an action potential and 2) water and salt transport in epithelial tissues. Mutations in this gene are associated with hereditary long QT syndrome, diabetics , Romano-Ward syndrome, Jervell and Lange-Nielsen syndrome  and familial atrial fibrillation , as well as impairment of cyclic AMP-stimulated intestinal secretion of chloride ions related to cystic fibrosis [21,22] and pathological forms of secretary diarrhea [23-25]. Furthermore, drug-induced acquired KCNQ1 and KCNQ1/KCNE dysfunctions also raise concerns of KCNQ1/KCNE as potential hERG-like drug safety issue in pharmaceutical development .
For their pharmacological responses, KCNQ1/KCNE heteromultimers function differently from KCNQ1 alone. Initial discovery of KCNQ1 modulators is focused on the KCNQ1 (and KCNQ1/KCNE1 IKs) inhibitors . In contrast to KCNQ1 channel blockers, only until recently have KCNQ1 channel activators/ potentiators been generating a lot of interests partially due to KCNQ1/KCNE activators might be useful agents to counteract the loss of delayed rectifier function in LQT syndromes, as well as counter target of other KCNQ family members for potential drugs for the treatment of epilepsy and neuropathic pain. Overall there are a very limited number of KCNQ1 activators/ potentiators, a further limited number of KCNQ1/E1 heteromultimer-specific modulators, and no reported KCNQ1/E2 or KCNQ1/E3 heteromultimer-specific modulators. This has hindered a more systematic study to understand the roles of on beta-subunits. Therefore it justifies the necessity of primary high throughput screen of KCNQ1 with the MLSMR library of >300,000-500,000 compounds covering large chemical space.
Principle of the assay
Patch clamp recording provides a high resolution, linear measure of channel activities. The purpose of this assay is to test the SAR compounds for KCNQ1 activators using automated population patch clamp electrophysiology system IonWorks (Molecular Devices). This assay employs automated patch clamp (Ionworks Quattro) to investigate the current responses of KCNQ1-CHO elicited by voltage clamp protocols in the presence or absence of test compounds. Compounds were tested in quadruplicates at varying concentrations
KCNQ1, activator, agonist, Concentration Response Curve, JHICC, Johns Hopkins, Molecular Libraries Probe Production Centers Network, MLPCN.
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Protocol for automated patch clamp on KCNQ1-CHO cells with voltage clamp
1. Cell culture: Cells are routinely cultured in DMEM/F12 medium, supplemented with 10% Fetal Bovine Serum (FBS), 50 IU/ml penicillin, 50 ug/ml streptomycin, and 500 ug/ml G418 by using 150mm dishes.
2. Split cells once they reach 80% to 90% confluence
2.1. Aspirate medium from culture, add 10 mL of PBS (without Ca2+ and Mg2+) to wash the cell monolayer.
2.2. Aspirate the PBS.
2.3. Add 5 mL of 0.05% Trypsin to the 150mm dish, leave dish undisturbed for 3~5 min at 37 to trypsinize the cells.
2.4. Add 20 mL of growth medium to neutralize the digestion of Trypsin.
2.5. Transfer cell suspension to 50 mL falcon tube and spin at 750 rpm for 4 min.
2.6. Remove supernatant and resuspend cells with 6 ml external solution, spin down at 450 rpm for 4 min.
2.7. Count the cells, adjust the cell density at 2x10;6 per ml.
3. Prepare 3x compound plates: test compounds are prepared using external solution;
4. Prepare Amphotericin B: dissolve 5 mg Amphotericin B with 180 uL DMSO, vortex for 1 min; transfer dissolved amphotericin B to 50 mL internal buffer, fill in the amphotericin B tube.
5. Fill the external solution in the buffer boat; fill the internal solution in the internal solution bottle.
6. Add the cells in the cell boat.
7. Load the protocol: The holding potential is -70 mV. To elicit the currents, cells were stimulated by 2,000 ms depolarizing step from -70 mV to +40 mV. Start the experiments.
8. Measure the currents at the steady state.
+40mV was used to evaluate compounds.
9. Calculate the percentage of current change for tested compounds with the following formula:
Percentage (%) =100* (Current (post-compound)-Current (pre-compound))/Current (pre-compound)
Percentage (%): Percentage of current inhibition observed after the application of the test compound.
Current (pre-compound): Current recorded before the test compound application
Current (post-compound): Current recorded after the test compound application
10. Outcome assignment
If the test compound causes activation effect on KCNQ1 in any concentrations tested and the dose response is generated, the compound is considered to be active.
If the test compound does not cause activation effect on KCNQ1 in any concentrations tested or a dose response is not generated, the compound is designated as inactive.
11. Score assignment
An inactive test compound is assigned the score of 0.
An active test compound is assigned the score of 100.
12. Internal buffer (40 mM KCl, 100 mM K-Gluconate,1 mM MgCl2, 2 mM CaCl2, 5 mM HEPES, pH 7.25)
13. External buffer (137 mM NaCl, 4 mM KCl, 1.8 mM CaCl2, 1 mM MgCl2, and 10 mM HEPES and 10 mM Glucose, pH 7.4)
Categorized Comment - additional comments and annotations
* Activity Concentration. ** Test Concentration.
Data Table (Concise)