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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.

 

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
Price
21480RH 237 [N-(4-Sulfobutyl)-4-(6-(4-(dibutylamino)phenyl)hexatrienyl)pyridinium, inner salt]5 mg100
21482RH 421 [N-(4-Sulfobutyl)-4-(4-(4- (dipentylamino)phenyl)butadienyl)pyridinium, inner salt] *CAS 107610-19-5*5 mg100
21483MM 1-43 [N-(3-Triethylammoniumpropyl)-4-(4-(dibutylamino)styryl)pyridinium dibromide] *CAS#: 149838-22-2*1 mg100
21485RH 414 [N-(3-Triethylammoniumpropyl)-4-(4-(4-(diethylamino)phenyl)butadienyl)pyridinium dibromide] *CAS#: 161433-30-3*5 mg153
21487MM 4-64 [N-(3-Triethylammoniumpropyl)-4-(6-(4-(diethylamino)phenyl)hexatrienyl)pyridinium dibromide]1 mg205
21489MM 2-10 [N-(3-Triethylammoniumpropyl)-4-(4-(diethylamino)styryl)pyridinium dibromide]1 mg100
21492TMA-DPH *CAS#: 115534-33-3*5 mg100
21495RH 795 *CAS#: 172807-13-5*1 mg132
21496Di-2-ANEPEQ [JPW 1114]5 mg205
21497Di-8-ANEPPS *CAS#: 157134-53-7*5 mg205

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

Cat#
Product Name
Unit Size
Price
21410DiBAC4(5) [Bis-(1,3-dibutylbarbituric acid)pentamethine oxonol]25 mg153
21411DiBAC4(3) [Bis-(1,3-dibutylbarbituric acid)trimethine oxonol]25 mg100
21414DiSBAC2(3) [Bis-(1,3-diethylthiobarbituric acid)trimethine oxonol]25 mg100
22030DiA [4-(4-(Dihexadecylamino)styryl)-N-methylpyridinium iodide]25 mg79
22033DiD labeling solution [1,1-Dioctadecyl-3,3,3,3-tetramethylindodicarbocyanine] *5 mM DMSO solution*10 mL205
22035DiIC12(3) perchlorate [1,1-Didodecyl-3,3,3,3-tetramethylindocarbocyanine perchlorate] 25 mg79
22038DiOC2(3) iodide [3,3-Diethyloxacarbocyanine iodide]25 mg79
22039DiOC3(3) iodide [3,3-Dipropyloxacarbocyanine iodide]25 mg79
22040DiOC7(3) iodide [3,3-Diheptyloxacarbocyanine iodide]25 mg79
22042DiOC16(3) perchlorate [3,3-Dihexadecyloxacarbocyanine perchlorate]25 mg79