Relaxation studies on cell membranes and lipid bilayers in the high electric field range

Abstract

Abstract Charge pulse experiments were performed on cells of the giant alga Valonia utricularis and on lipid bilayer membranes. For low electric fields (in the order of 100 mV) the resulting membrane voltage U m is a linear function of the injected charge. For high voltages U m (in the order of one volt) the relation between injected charge Q and resulting voltage U m is no longer seen for both systems and a state of high conductance is observed without mechanical damage of the membranes. Because of the high conductance the membranes cannot be charged to voltages higher than a critical one, which is denoted as breakdown voltage U t . The breakdown voltage U c was found to be a function of the charging time needed to obtain breakdown. In the experiments with cells of Valonia utricularis , where presumably the breakdown occurs in both tonoplast and plasmalemma membrane, the breakdown voltage varies at 18 °C between 2.4 V (charging time 800 ns) and 750 mV (charging time 500 μs). A similar pulse length dependence was also found for lipid bilayer membranes. Between 300 ns and 5 μs at 25 °C and between 100 ns and 2 μs at 40 °C, U c showed a strong dependence on charging time of the membrane and decreased from 1.2 V to 0.5 V (25 °C) and from 1 to 0.4 V (40 °C). For other charging times below and above these ranges the breakdown voltage seemed to be constant. The results indicate that the breakdown phenomenon occurs in less than 10 ns. The pulse length dependence of the breakdown voltage found for both cell membrane and lipid bilayer is consistent with the electro-mechanical model proposed earlier. However, it seems possible that at short charging times (where the breakdown voltage reaches a plateau) other processes (involving the Born energy) become possible.