First, the electrical
properties of the membrane can be altered by the physical addition of exogenous chromophores. In Epigenetics Compound Library supplier fact, most voltage dyes either are charged or have significant dipoles, in order to be sensitive to changes in the electric field. But because they need to insert themselves in the plasma membrane for effective voltage measurements, they can significantly alter the electrical charge of the membrane and distort its normal behavior. In particular, the addition of fixed charges increases the membrane capacitance, to the point that staining with a voltage-sensitive dye can lead to major reductions in the action potential conduction velocity (Blunck et al., 2005). The unwanted electrical effects NVP-BKM120 chemical structure of the voltage dyes in membranes are not their only side effect. In fact, many voltage indicators have substantial toxicity and a variety of pharmacological effects, probably related to their localization in a key cellular component such as the plasma membrane. Moreover, these effects are not easy to generalize and depend on the specific dye and the specific preparation used. For example, a few voltage-sensitive
dyes have been shown to modulate the ionotropic GABA-A receptor with an effectiveness similar to that of drugs designed specifically for that purpose (Mennerick et al., 2010). Therefore, for each novel voltage chromophore a substantial amount of “homework” is required for each new preparation. Assuming that all the previously mentioned challenges have been met, there remains another substantial difficulty when using voltage indicators: calibrating their signals. Translating an optical signal into an electrical one requires a good understanding of the biophysical mechanisms of voltage sensitivity. Electron transport chain While for some of the mechanisms and chromophores there can be linear
relationship between voltage and optical signal, in many experiments this is not demonstrated. Understandably, neuroscientists are often interested in the overall biological results and concentrate their efforts on getting the voltage measurements to work, rather than on understanding the precise details of how their measurements have actually worked. It is also likely that multiple mechanisms with differing timescales contribute to the overall voltage sensitivity of these molecules, confounding the calculated relation between photons measured and electrical signals. In simple situations, one can carry out a combined optical and electrical measurement of the same signal and thus have a direct calibration of the optical signal, but often such combined experiments are not practical, because the optical measurements are carried out precisely in locations or regimes where electrical measurements are impossible.