Transmembrane potential difference principles

The difference in the transmembrane potential, of the mitochondria, between normal epithelial and carcinoma cells is at least 60 mV more negative in the latter due to the higher metabolic requirements of tumor cells [58], According to the Nernst equation, this difference would lead to a 10-fold increase in the cellular uptake of lipophilic cations [59], This is the principle for the superior accumulation of [ Tc]MIBI in tumor cells when compared to the epithelial or connective surrounding tissues. 

The vesicle assay previously used ves a good survey of transporter activity under a fixed set of conditions. However it is not suited to exploration of transport activity as a function of the sign and magmtude of the transmembrane potential. Bilayer conductance, or single channel recording techniques are required (21). In this techmque, a lipid bilayer is formed across a small hole in a Teflon barrier, by direct application of the lipid in decane to the hole. Under favorable conditions, Ae lipid tl s to a bilayer membrane which electrically isolates the two halves of the cell. T icdly KCl is used as an electrol, and electrical contact is made via Ag/AgQ wires directly inserted into the solutions. A high impedance operational amplifier circuit (bUayer clamp) can then be used to apply a fixed transmembrane potential and to monitor the current which flows as a function of time. The two sides of the membrane are independently accessible, so different sequences of transporter addition, control of pH, and other variables are in principle j ssible. 

The main principles of membrane phosphorylation are the same in chloroplasts, mitochondria, and photosynthetic bacteria. In this section, in order to analyze the role of protonmotive force in the processes of energy transduction in biomembranes, we will focus our attention on the consideration of proton-transport processes in chloroplasts. In thylakoids the ApH is the main component of transmembrane difference in electrochemical potentials of hydrogen ions, AjuH+ = Acp — 2.3(RT/F)ApH. The conductivities of the thylakoid membrane for the majority of cations (Mg ", Na ), existing... 

---