Identification of Novel Modulators of Cl- dependent Transport Process via HTS: Secondary Assay 3 with KCC2 cells
Cation-chloride cotransporters such as K-Cl cotransport and Na-K-2Cl cotransport play major roles in a variety of physiological settings, including the modulation of GABAergic synaptic transmission. For instance, KCC2, a neuronal-specific K-Cl cotransporter is up-regulated in the brain during postnatal development, and is responsible for lowering the intracellular Cl- concentration in neurons, more ..
BioActive Compounds: 1815
Vanderbilt Screening Center for GPCRs, Ion Channels and Transporters
Assay Provider: Eric Delpire
Assay Provider Affliation: Vanderbilt University
Grant Title: Identification of Novel Modulators of Cl- dependent Transport Process via HTS
Grant Number: R21NS053658-01
Cation-chloride cotransporters such as K-Cl cotransport and Na-K-2Cl cotransport play major roles in a variety of physiological settings, including the modulation of GABAergic synaptic transmission. For instance, KCC2, a neuronal-specific K-Cl cotransporter is up-regulated in the brain during postnatal development, and is responsible for lowering the intracellular Cl- concentration in neurons, thus promoting GABA inhibition. Reduction in KCC2 expression results in brain hyperexcitability, as demonstrated by animal models. Furthermore, KCC2 expression is decreased in brain tissue isolated from epileptic patients.
There are very few pharmacological agents that affect K-Cl cotransporters. First, there are no specific inhibitors of K-Cl cotransporters. Furosemide is mostly used to inhibit K-Cl cotransporter function, but the diuretic is not very potent and is not specific as it inhibits the Na-K-2Cl cotransporter (diuretic effect), many Cl- channels including the GABAA receptor. Finding new inhibitors will provide important tools for the study of KCC2 in modulating inhibitory neurotransmission. Second, there are also no compounds known to activate K-Cl cotransporter, except for N-ethylmaleimide, which affects many cellular processes as an unspecific alkylating agent. Finding a specific agent that increase KCC2 function would potentially have therapeutic value, as increased KCC2 function reduces susceptibility to epileptic seizures.
The purpose of this assay was to test compounds identified as 'hits' from the Molecular Libraries Small Molecule Repository (MLSMR) at a single concentration in the presence of ouabain and bumetanide against cells expressing the cation-chloride cotransporter, KCC2. Compounds that were not active in the presence of bumetanide, a known KCC2 inhibitor, were considered potential KCC2 probe molecules.
1. Human embryonic kidney cells expressing KCC2 were plated at 20,000 cells/well in Dulbecco's modified medium (DMEM), 41.6% F12 (Gibco catalog 11320-033) in 384 well plate, black, clear bottom, poly-D-lysine coated (Greiner catalog 781946).
2. Cells were incubated overnight at 37 degrees C in 5%CO2.
3. Cells were loaded with 0.5 micromolar FluoZin2-AM dye (Invitrogen catalog number F24189) in assay buffer (Hanks Buffered Salt Solution, 20 mM HEPES, 0.2 mM oubain, 2mM bumetanide) for 48 minutes.
4. Dye was removed and the plate imaged using the Hamamatsu FDSS kinetic plate reader equipped with 480 nanometer excitation and 540 nanometer emission filters.
5. Compounds in DMSO were added to a final concentration of 10 micromolar (0.1% DMSO final concentration).
6. Thallium buffer stimulus (125 mM sodium bicarbonate, 12 mM thallium sulfate, 1 mM magnesium sulfate, 1.8 mM calcium sulfate, 5 mM glucose, 10 mM HEPES, pH 7.3.) was added and images collected at 1 Hz.
7. Assay buffer containing DMSO (0.1% final concentration) was used as the negative control and 2 mM bumetanide was used as the positive control on each plate.
1. The raw fluorescence intensities were divided by the initial fluorescence, and the slope from 10 to 20 seconds after thallium addition was calculated and labeled 'Value1' for replicate 1 and 'Value2' for replicate 2.
2. Comparison of each compound well with the mean + 3 standard deviations of the bumetanide control population on a per plate basis resulted in wells designated as 'Outcome' = 'Active' and 'Score' = '100' based on a statistical significance of greater than 99.7 % confidence. Wells that did not significantly vary were labeled 'Outcome' = 'Inactive' and 'Score' = '0'. Wells where duplicate testing resulted in discrepant values were designated 'Outcome' = 'Inconclusive' and 'Score' = '50'.
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