Cell membrane activity measurement

Edelfors S, Raven-Jonsen A. 1992. Effect of organic solvents on nervous cell membrane as measured by changes in the calcium magnesium ATPase activity and fluidity of synaptosomal membrane. Pharmacology and Toxicology 70(3) 181-187. 

The possibility that vitamin C could act as a pro-oxidant is not just theoretical. A common test for the potency of an antioxidant actually depends on vitamin C to promote injury. The method begins by stimulating free-radical chain reactions in a preparation of cell membranes, then measures how well antioxidants can stop the process in its tracks. The chain reactions are started using a concoction of iron and vitamin C — iron to catalyse the reaction, and vitamin C to regenerate the active iron. If this situation were ever to take place in the body, the effect could be catastrophic. 

Fig. 21.3. Two-micropipette current-clamp recording and effect of maintained application of 30 pM levamisole, which produces a 15 mV depolarization (upward movement of trace). The downward transients are the result of injected current pulses used to measure membrane conductance. The trace gets narrower as the input conductance increases from 2.35 pS to 4.35 pS as the levamisole ion channels open. The peak amplitude of the membrane potential response and change in input conductance are used as an assay of the number and activity of the levamisole ion channel receptors present in the muscle cell membrane. The response was fully reversible on washing (not shown).

Since active transport mechanisms require energy, the incubation temperature during the assay plays a crucial role. At 4°C, the fluidity of the cell membrane is reduced, the metabolism of the cell is downregulated, and energy-dependent transport processes are suppressed. Consequently, the amount of cell-associated target system refers mainly to the cytoadhesive fraction. In contrast, incubation at 37°C increases the fluidity of the cell membrane and the metabolic activity to an optimum, so both cytoadhesion and cytoinvasion occur at the same time. Thus, the uptake rate can be calculated from the difference in signal intensity measured upon incubation at both respective temperatures. 

The antioxidant activity afforded by NO is most important if it translates into a meaningful therapeutic event. To test the importance of this reaction pathway to cell survival, we compared viability of the cells exposed to in the presence or absence of NO, When cells are exposed to 20 pM there was appreciable loss of cell membrane integrity as measured by trypan blue dye exclusion (Kelley et al, 1999) the addition of NO deaeased cell membrane damage (Figure 6). 

More recently, B. Goldstein and McDonagh demonstrated that the native protein fluorescence (280-nm excitation, 330-nm emission) of red-cell membranes exposed in vitro to ozone at 1 ppm was a somewhat more sensitive indicator of ozone effect than other characteristics measured in the same em, including oxidation of cell-membrane sulfhydiyl groups, loss of acetylcholinesterase activity, and formation of lipid peroxide breakdown products. 

Ion-selective microelectrodes [18, 70,71, 164] are chiefly used for measurement of ion activities in individual cells and in intracellular liquid. They were developed from micropipettes, which are miniature liquid bridges used for measurement of cell membrane potentials [94]. Micropipettes and ion-selective microelectrodes are made using commercial drawing devices. Ion-selective... 

The hepatocytes was subcultured for 2 days and their albumin secretion activity was measured. The TRS-harvested hepatocytes showed nearly the same albumin secretion activity as the primary culture, whereas the ERS-harvested ones showed only 20% activity. This finding is important because no subculture of hepatocyte has ever been successful, owing to a possible proteolytic disruption of cell-membrane structure (especially cell-cell adhesion) in the course of trypsin treatment. 

In in vitro systems, criteria of toxicity will generally be measurements of either specific biochemical changes, such as ATP level or protein synthesis, or general indicators such as cell metabolic activity, viability, or membrane damage as indicated by dye uptake or enzyme leakage. 

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