Methods for measuring chloride channel conductivity
The invention provides non-radioactive methods to assay for functional chloride channels. The methods colorimetrically detect the amount of iodide conducted by a chloride channel. They can be easily adapted for high throughput assays or screenings.
1 . A method for measuring chloride channel conductivity, comprising the steps of:
a) contacting a chloride channel with iodide; and
b) calorimetrically detecting the amount of iodide conducted by the chloride channel.
2 . The method of claim 1 wherein the method measures the influx of iodide into a cell or membrane vesicle having the chloride channel, wherein the contacting step comprises incubating a cell or membrane vesicle having the chloride channel in a liquid solution comprising iodide and separating the cell or membrane vesicle from the liquid solution; and wherein the calorimetric detection step comprises measuring the amount of iodide inside the cell or membrane vesicle using a colorimetric detection method.
3 . The method of claim 2 , wherein the cell or membrane vesicle having the chloride channel is obtained from a patient.
4 . The method of claim 1 wherein the method measures the efflux of iodide out of an iodide-loaded cell or membrane vesicle having the chloride channel, wherein the contacting step comprises incubating the iodide-loaded cell or membrane vesicle having the chloride channel in a liquid solution that is substantially free of iodine and separating the cell or membrane vesicle from the liquid solution; and wherein the calorimetrically detecting step comprises measuring the amount of iodide inside the cell or membrane vesicle, or in the liquid solution, using a calorimetric detection method.
5 . The method of claim 4 , wherein the cell or membrane vesicle having the chloride channel is obtained from a patient.
6 . The method of claim 4 , wherein the colormetricallly detecting step further comprises the step of determining the ratio of the amount of iodide in the solution to the amount of iodide inside the cell or membrane vesicle.
7 . The method of claim 1 , further comprising the step of opening or activating the chloride channel prior to the step of calorimetrically detecting the amount of iodide conducted by the chloride channel.
8 . The method of claim 1 , wherein said chloride channel is selected from the group consisting of a voltage-gated chloride channel, a ligand-gated chloride channel, a swelling-activated chloride channel, a calcium-activated chloride channel, and a CLIC chloride channel.
9 . The method of claim 8 , wherein said chloride channel is a receptor for γ-aminobutyric acid or glycine.
10 . The method of claim 8 , wherein said chloride channel is cystic fibrosis transmembrane conductance regulator.
11 . The method of claim 1 , wherein the calorimetric detection method is based on the Sandell and Kolthoff reaction:
12 . The method of claim 1 , wherein the calorimetric detection method involves the substrate starch.
13 . The method of claim 1 , wherein the colorimetric detection method involves the substrate 3,3′,5,5′-tetramethylbenzidine.
14 . The method of claim 1 , wherein the calorimetric detection method involves the substrate thiocyanate.
15 . A method for determining an effect of a test compound on the conductivity of a chloride channel, comprising the steps of
a) contacting the chloride channel with the test compound and iodide;
b) calorimetrically detecting the amount of iodide conducted by the chloride channel; and
c) comparing the amount of iodide detected in step b) with that of a control wherein the chloride channel is not contacted with the test compound.
16 . The method of claim 15 wherein the method measures the influx of iodide into a cell or membrane vesicle having the chloride channel, wherein the contacting step first comprises the step of: incubating the cell or membrane vesicle having the chloride channel in a liquid solution containing iodide then contacting the cell or membrane vesicle with the test compound and separating the cell or membrane vesicle from the liquid solution; and, wherein the colorimetrizallly detecting step comprises the step of measuring the amount of iodide inside the cell or membrane vesicle using a colorimetric detection method.
17 . The method of claim 15 wherein the method measures the efflux of iodide out of an iodide-loaded cell or iodide loaded membrane vesicle comprising a chloride channel, wherein the contacting step comprises incubating the iodide-loaded cell or membrane vesicle having the chloride channel in a liquid solution that is substantially free of iodine and contacting the cell or membrane vesicle with the test compound and separating the cell or membrane vesicle from the liquid solution; and wherein the detecting step comprises measuring the amount of iodide inside the cell or membrane vesicle, or in the liquid solution, using a colorimetric detection method.
18 . The method of claim 17 , further comprising a step of determining the ratio of the amount of iodide in the solution to the amount of iodide inside the cell or membrane vesicle.
19 . The method of claim 15 , further comprising the step of opening or activating the chloride channel prior to the colorimetrizallly detecting step.
20 . The method of claim 15 , wherein said chloride channel is selected from the group consisting of a voltage-gated chloride channel, a ligand-gated chloride channel, a swelling-activated chloride channel, a calcium-activated chloride channel, and a CLIC chloride channel.
21 . The method of claim 20 , wherein said chloride channel is a receptor for γ-aminobutyric acid or glycine.
22 . The method of claim 20 , wherein said chloride channel is cystic fibrosis transmembrane conductance regulator.
23 . The method of claim 15 , wherein the colorimetric detection method is based on the Sandell and Kolthoff reaction:
24 . The method of claim 15 , wherein the calorimetric detection method involves the substrate starch.
25 . The method of claim 15 , wherein the colorimetric detection method involves the substrate 3,3′,5,5′-tetramethylbenzidine.
26 . The method of claim 15 , wherein the colorimetric detection method involves the substrate thiocyanate.