Systems biology analysis of changes in potential across plasma membrane: Physiological implications

Abstract

Variation of the membrane potential difference (PD) across plasma membrane is considered in terms of one or more ion transporter populations changing their conductance and activation kinetics. Slow changes occurring over minutes can be investigated by the current voltage (I/V) technique. In some cases, data are sufficient to model electrical characteristics of each transporter population and their evolution with time. The proton pump at the plasma membrane of the salt-sensitive Characeae Chara australis provides an example of single transporter changing conductance against a steady background. The rise and fall in proton pump conductance may be prompted by circadian oscillations of indoleamines IAA and melatonin, measured in growing thalli of characean plants. In response to abiotic stress, two or more transporter populations change conductance and/or PD dependence. The voltage clamp to extreme negative PD levels transiently inhibits the proton pump in C. australis, activating H+/OH−channels, increasing the background conductance, and opening inward rectifier channels at more depolarized PDs. An increase in medium salinity (after pre-treatment with isotonic sorbitol medium) results in similar response, which is preceded by a typical noise in membrane PD. In salt-tolerant Characeae Lamprothamnium sp., increase in salinity (or osmolarity) provokes an increase in proton pumping as well as increase in background conductance and opening of the inward rectifier channels at more depolarized PDs to effect turgor regulation. The hypoosmotic turgor regulation also involves a complex interaction of several transporters, initiated by the increase of turgor pressure, [Ca2+]cyt increase, and PD changes. A detailed modeling is in progress for most of these responses. The examples demonstrate the analytical and predictive power of the I/V methodology coupled with the systems biology modeling and monitoring of biochemical changes.