Potassium channels measurement

Cha, A., Snyder, G. E., Selvin, P. R., and Bezanilla, F. (1999). Atomic scale movement of the voltage-sensing region in a potassium channel measured via spectroscopy. Nature 402, 809-813. 

One type of information which can only be obtained from fluctuation analysis concerns the size of the elementary events. Under the assumption that ionic channels in nerve membranes have only one non-zero conductance value, this value can be estimated from measurements of the variance of current fluctuations associated with the random opening and closing of channels. The conductance of single sodium or potassium channels, measured with this method both in myelinated and unmyelinated nerve fibers, ranges between 4 and 12 pS. 

Cloned Human Potassium Channels. Assessment of effects on cloned HERG K channels stablely expressed in a cell line by measurement of whole cell K current (lKr) using voltage clamp. Other cloned human ion channels (e.g., KvLQTl/minK-IKs currents) are also possible. 

Cardiac Action Potential In Vitro Purkinje Fibers. Intracellular recording of action potentials from cardiac Purkinje fibers isolated from dog or sheep ventricle. Measurement of maximum rate of depolarization and action potential duration to detect sodium and potassium channel interactions, respectively, according to recommendations in EM A CPMP Points to Consider document, CPMP 986/96 (1998). 

The 1960s and 1970s also saw increasingly sophisticated approaches to the investigation of ion channels in nerve and muscle. Armstrong used quaternary ammonium ions as blocking agents to probe the nature of potassium channels and Hille (1984) measured the permeability of channels to ions of different sizes, and so was able to estimate the minimum dimensions of the channel pore. These indirect... 

Patch-clamp techniques using isolated ventricular myocytes may be used measure potassium channel function to clarify the mechanisms underlying the development of torsade de pointes ventricular arrhythmias (Salata et al. 1995 Drolet et al. 1999 Kalifa et al. 1999). 

Mannuzzu, L. M., Moronne, M. M., and Isacoff, E. Y (1996). Direct physical measure of conformational rearrangement underlying potassium channel gating. Science 271, 213-216. 

Yusaf, S. P., Wray, D., and Sivaprasadarao, A. (1996). Measurement of the movement of the S4 segment during activation of a voltage-gated potassium channel. I flugers Arch. Eur. J. Physiol. 433, 91-97. 

Potassium channels can have a frequency of one or more channels per square micrometer of membrane surface area. Cellular control can be exerted on the opening of such K+ channels, because concentrations of cytosolic Ca2+ above 3 x 10-4 mol m-3 (0.3 p,M) can inhibit channel opening. Other ion channels in plant membranes are specific for Ca2+ or Cl-. Besides being sensitive to the electrical potential difference across a membrane, some channels apparently open upon stretching of a membrane. Also, many plant cells are excitable and can transmit action potentials, a process in which ion channels are undoubtedly involved. For example, action potentials have been measured for plants responsive to tactile stimuli, such as rapid leaf movements in Mimosa pudica and insectivorous plants (Dionaea spp., Drosera spp.), as well as along the phloem for many species. In addition, ion channels are involved in the long-term maintenance of specific ion concentrations in plant cells. 

Chill JH, Louis JM, Baber JL, Bax A. Measurement of 15N relaxation in the detergent-solubilized tetrameric KcsA potassium channel. J. Biomol. NMR 2006 36 123-136. 

Kirsch GE, Trepakova ES, Brimecombe JC, et al. Variability in the measurement of hERG potassium channel inhibition Effects of temperature and stimulus pattern. / Pharmacol Toxicol Methods. 2004 50(2) 93-101. 

To demonstrate that we could immobilize a voltage sensor, we first turned to Shaker potassium channels, because (i) gating currents, which primarily reflect S4 movement, are easy to measure, and (ii) the channels have tetrameric symmetry. We used a non inactivating variant of Shaker into which we introduced the cysteine mutant A359C, located at the extracellular end of the S4 segment. After exposure to BPMTS each channel has four labelled S4 segments. 

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