Clamping measurements

Let the setup cool to room temperature. Bring the pressure in it to atmospheric by lifting or lowering the beaker with water or the flask. Close the clamp. Measure the volume of the water in the beaker by pouring it into a measuring cylinder. Weigh the test tube on the analytical balance with the same accuracy as before. 

Methfessel C, Witzemann V, Takahashi T et al. (1986) Patch clamp measurements on Xenopus laevis oocytes currents through endogenous channels and implanted acetylcholine receptor. Pfltigers Arch 407 577-588... 

As implemented by Sukharev and Guy, the combination of patch-clamp measurements with disulfide trapping provides a sensitive approach for testing models of the open state by characterizing the consequences of disulfide bond formation between specific cysteines on... 

The cadherin-like proteins have been successfully expressed in heterologous systems and the recombinant proteins have similar toxin-binding capabilities as the native proteins [133,151-153]. Insect cells expressing the cadherin-like protein also exhibited CrylAa toxin-induced cell swelling and whole cell patch clamp measurements indicating possible pore formation [147]. 

Sparteine is a drug with antiarrhythmic properties. It has been deduced from pharmacological and electrophysiological studies that sparteine acts via a reduction of the Na inward current, e.g. during the upstroke of cardiac action potentials. This process was elucidated by the determination of sodium currents, in isolated muscle fibbers, by loose patch clamp measurements [236]. The IC50 value for half-maximal blocking of the sodium current was 168.8 )iM, which is in accordance witli the antiarrhythmic activity of sparteine. The importance of sparteine on Na channels inhibition was further analysed because of its potencial strong interference in neuronal transmission, particularly in herbivores. This emphasizes the role of sparteine as a chemical defence compound for the plants that produce it. 

The experimental results shown in Figure 7-38 demonstrate that inactivation of channels depends on the ball domains, occurs after channel opening, and does not require the ball domains to be covalently linked to the channel protein. In other experiments, mutant channels lacking portions of the 40-residue chain connecting the ball to the SI helix were expressed in frog oocytes. Patch-clamp measurements of channel activity showed that the shorter the chain. 

Another way to estimate the selectivity from voltage-clamp measurements is to use the reversal potential (zero early current) [21,22] and calculate the ratio P-/P of the Goldman equation which would account for the change in reversal potential induced by the organic cation. The ratio calculated in this last case is... 

The direct measurement of the time course of the influx of Na during a depolarising rectangular voltage-clamp pulse, and during an action potential discussed in Section 3b, resolved the question of specificity of the voltage-clamp measurements, and the concept of two independent kinetic components in the membrane currents, each representing an ionic pathway with different ionic selectivity, was established without doubt. 

Noble, D. and RW. Tsien (1969). Reconstruction of the repolarization process in cardiac Purkinje fibres based on voltage clamp measurements of membrane current. /. Physiol. (Lond.) 200, 205-231. 

Whole-cell patch clamp measurements were conducted 36—72 h after propagation of theTRPM8 stable cell lines or transient transfection of target clones. The extracellular solution contained (in mM) 137 NaCl, 5 KCl, 1 MgCl, 10 glucose, and 10 HEPES, pH 7.4. Borosilicate glass pipettes (World Precision Instruments,... 

Electrical measurements on cells are discussed in other entries in the encyclopedia Patch Clamp Measurements On-CThip. The focus here is on the basic cell electrical responses assayed in microchannels, most of which have been developed in the context of cell-based biosensors. These studies typically evaluate cell action potential which is a net electrical change in cells resulting from changing concentrations of intracellular ions. Action potentials are important physiologically because they result in the... 

Patch Clamp Measurements On-Chip, Fig. 1 Patch clamp technique and an amended equivalent circuit... 

For patch clamp measurements, the PDMS planar electrode array was plasma oxidized and then motmted in the recording system shown in Fig. 6. To electrically isolate each electrode, the partition was sealed onto the chamber bottom over an array of openings that each contained an Ag-AgCl wire and suction tubing. The Ag-AgCl wire was connected to the multiplexer chip mounted on the circuit board under the chamber. The multiplexer then connected to the input of the amplifier. The tubing connected to a suction manifold that permitted individual or global suction. 

While an array of analytical techniques has been developed to study various aspects of cells (please see Cell Assays in Microfluidics), this entiy is focused on chemical cytometry. As mentioned above, chemical cytometry refers to methods in which intracellular constituents of a single cell are analyzed by means of a chemical separation. Such methods typically employ capillary electrophoresis for separations, combined with laser-induced fluorescence (LIF) or amperometry for detection. We refer readers to other entries for detailed descriptions of other methods used to evaluate the contents of cells ( Patch Clamp Measurements On-Chip, Mass Spectrometry on a Chip). 

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