Membrane Potential and Channels

Membrane potential is the difference in voltage between the interior and exterior of a cell. The membrane potential allows a cell to function as a battery, providing power to operate a variety of molecular devices embedded in the membrane. In electrically excitable cells such as neurons, membrane potential is used for transmitting signals between different parts of a cell. Opening or closing of ion channels at one point in the membrane produces a local change in the membrane potential, which causes an electric current to flow rapidly to other points in the membrane. Ion channels have been identified as important drug discovery targets.

The plasma membrane of a cell typically has a transmembrane potential of approximately ?70 mV (negative inside) as a consequence of K+, Na+ and Cl concentration gradients that are maintained by active transport processes. Potentiometric probes offer an indirect convenient method of detecting the translocation of these ions although the fluorescent ion indicators can be used to directly measure changes in specific ion concentrations. Potentiometric optical probes enable researchers to perform membrane potential measurements in organelles and in cells that are too small for microelectrodes. Moreover, in conjunction with imaging techniques, these probes can be employed to map variations in membrane potential across excitable cells, in perfused organs and ultimately in the brain in vivo with spatial resolution and sampling frequency that cannot be obtained using microelectrodes. Increases and decreases in membrane potential play a central role in many physiological processes, including nerve-impulse propagation, muscle contraction, cell signaling and ion-channel gating.

Potentiometric probes are important tools for studying these processes, as well as for visualizing mitochondria (which exhibit transmembrane potentials of approximately ?150 mV, negative inside matrix), for assessing cell viability and for high-throughput screening of new drug candidates. Potentiometric probes include the cationic or zwitterionic styryl dyes, the cationic carbocyanines and rhodamines, and the anionic oxonols. The class of dye determines factors such as accumulation in cells, response mechanism and toxicity. Selecting the best potentiometric probe for a particular application can be complicated by the substantial variations in their optical responses, phototoxicity and interactions with other molecules. There are two classes of membrane potential probes based on their response mechanisms: fast response and slow response membrane potential dyes.

Fast Response Membrane Potential Probes

Fast-response probes have their fluorescence in response to a change in the surrounding electric field. Their optical response is sufficiently fast to detect transient (millisecond) potential changes in excitable cells, including single neurons, cardiac cells and intact brains. However, the magnitude of their potential-dependent fluorescence change is often small, typically 0.02–0.1% fluorescence intensity change per mV.

Slow Response Membrane Potential Probes

Slow-response probes exhibit potential-dependent changes in their transmembrane distribution that are accompanied by a fluorescence change. The magnitude of their optical responses is much larger than that of fast-response probes, typically a 1% fluorescence change per mV. Slow-response probes, which include cationic carbocyanines and rhodamines and anionic oxonols, are suitable for detecting changes in average membrane potentials of nonexcitable cells caused by respiratory activity, ion-channel permeability, drug binding and other factors.

Product Ordering Information

Table 1. Ordering Info for Fast Response Membrane Potential Probes Products

Cat# Product Name Unit Size
15257 Amplite™ Fluorimetric Total NAD and NADH Assay Kit *Red Fluorescence* 400 Tests
15258 Amplite™ Colorimetric Total NAD and NADH Assay Kit 400 Tests
15261 Amplite™ Fluorimetric NADH Assay Kit *Red Fluorescence* 400 Tests
15263 Amplite™ Fluorimetric NAD/NADH Ratio Assay Kit *Red Fluorescence* 250 Tests
15271 Amplite™ Colorimetric NADH Assay Kit 400 Tests
15273 Amplite™ Colorimetric NAD/NADH Ratio Assay Kit 250 Tests
15275 Amplite™ Colorimetric Total NAD and NADH Assay Kit *Enhanced Sensitivity* 400 Tests
15280 Amplite™ Fluorimetric NAD Assay Kit *Blue Fluorescence* 200 Tests

Table 2. Ordering Info for NADP/NADPH Products

Cat# Product Name Unit Size
15260 Amplite™ Colorimetric Total NADP and NADPH Assay Kit 400 Tests
15262 Amplite™ Fluorimetric NADPH Assay Kit *Red Fluorescence* 400 Tests
15264 Amplite™ Fluorimetric NADP/NADPH Ratio Assay Kit *Red Fluorescence* 250 Tests
15265 ReadiUse™ NADPH Regenerating Kit 1000 Tests
15266 ReadiUse™ NADP Regenerating Kit 200 Tests
15272 Amplite™ Colorimetric NADPH Assay Kit 400 Tests
15274 Amplite™ Colorimetric NADP/NADPH Ratio Assay Kit 250 Tests
15276 Amplite™ Colorimetric Total NADP and NADPH Assay Kit *Enhanced Sensitivity* 400 Tests
15281 Amplite™ Fluorimetric NADP Assay Kit *Blue Fluorescence* 200 Tests
15295 Cell Meter™ Intracellular NADH/NADPH Fluorescence Imaging Kit *Deep Red Fluorescence* 100 Tests


Cat# Product Name Unit Size
21480 RH 237 [N-(4-Sulfobutyl)-4-(6-(4-(dibutylamino)phenyl)hexatrienyl)pyridinium, inner salt] 5 mg
21482 RH 421 [N-(4-Sulfobutyl)-4-(4-(4- (dipentylamino)phenyl)butadienyl)pyridinium, inner salt] *CAS 107610-19-5* 5 mg
21483 MM 1-43 [N-(3-Triethylammoniumpropyl)-4-(4-(dibutylamino)styryl)pyridinium dibromide] *CAS#: 149838-22-2* 1 mg
21485 RH 414 [N-(3-Triethylammoniumpropyl)-4-(4-(4-(diethylamino)phenyl)butadienyl)pyridinium dibromide] *CAS#: 161433-30-3* 5 mg
21487 MM 4-64 [N-(3-Triethylammoniumpropyl)-4-(6-(4-(diethylamino)phenyl)hexatrienyl)pyridinium dibromide] 1 mg
21489 MM 2-10 [N-(3-Triethylammoniumpropyl)-4-(4-(diethylamino)styryl)pyridinium dibromide] 1 mg
21492 TMA-DPH *CAS#: 115534-33-3* 5 mg
21495 RH 795 *CAS#: 172807-13-5* 1 mg
21496 Di-2-ANEPEQ [JPW 1114] 5 mg
21497 Di-8-ANEPPS *CAS#: 157134-53-7* 5 mg

Table 2. Ordering Info for Slow Response Membrane Potential Probes Products

Cat# Product Name Unit Size
21410 DiBAC4(5) [Bis-(1,3-dibutylbarbituric acid)pentamethine oxonol] 25 mg
21411 DiBAC4(3) [Bis-(1,3-dibutylbarbituric acid)trimethine oxonol] 25 mg
21414 DiSBAC2(3) [Bis-(1,3-diethylthiobarbituric acid)trimethine oxonol] 25 mg
22030 DiA [4-(4-(Dihexadecylamino)styryl)-N-methylpyridinium iodide] 25 mg
22033 DiD labeling solution [1,1-Dioctadecyl-3,3,3,3-tetramethylindodicarbocyanine] *5 mM DMSO solution* 10 mL
22035 DiIC12(3) perchlorate [1,1-Didodecyl-3,3,3,3-tetramethylindocarbocyanine perchlorate] 25 mg
22038 DiOC2(3) iodide [3,3-Diethyloxacarbocyanine iodide] 25 mg
22039 DiOC3(3) iodide [3,3-Dipropyloxacarbocyanine iodide] 25 mg
22040 DiOC7(3) iodide [3,3-Diheptyloxacarbocyanine iodide] 25 mg
22042 DiOC16(3) perchlorate [3,3-Dihexadecyloxacarbocyanine perchlorate] 25 mg
22044 DiIC16(3) perchlorate [1,1-Dihexadecyl-3,3,3,3-tetramethylindocarbocyanine perchlorate] 25 mg
22045 DiOC5(3) iodide [3,3-Dipentyloxacarbocyanine iodide] 25 mg
22046 DiOC6(3) iodide [3,3-Dihexyloxacarbocyanine iodide] 25 mg
22050 DiIC12(3)-DS [1,1-Diododecyl-3,3,3,3-tetramethylindocarbocyanine-5,5-disulfonic acid] 5 mg
22051 DiIC12(5)-DS [1,1-Diododecyl-3,3,3,3-tetramethylindodicarbocyanine-5,5-disulfonic acid] 5 mg
22052 DiIC18(3)-DS [1,1-Dioctadecyl-3,3,3,3-tetramethylindocarbocyanine-5,5-disulfonic acid] 5 mg
22054 DiIC18(5)-DS [1,1-Dioctadecyl-3,3,3,3-tetramethylindodicarbocyanine-5,5-disulfonic acid] 5 mg
22056 DiIC1(5) iodide [1,1,3,3,3,3-Hexamethylindodicarbocyanine iodide] 25 mg
22066 DiO perchlorate [3,3-Dioctadecyloxacarbocyanine perchlorate] 25 mg
22070 DiR iodide [1,1-dioctadecyl-3,3,3,3-tetramethylindotricarbocyanine iodide] 25 mg
22073 DiSC2(3) [3,3-Diethylthiacarbocyanine iodide] 25 mg
22076 DiSC3(5) [3,3-Dipropylthiadicarbocyanine iodide] 25 mg
22077 DiSC2(7) [3,3-Diethylthiatricarbocyanine iodide] *CAS#: 3071-70-3* 25 mg
22101 DiI iodide [1,1-Dioctadecyl-3,3,3,3- tetramethylindocarbocyanine iodide] 100 mg
22102 DiI perchlorate [1,1-Dioctadecyl-3,3,3,3-tetramethylindocarbocyanine perchlorate] *CAS 41085-99-8* 100 mg
22103 DiI triflate [1,1-Dioctadecyl-3,3,3,3-tetramethylindocarbocyanine triflate] 100 mg


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