Nonlinear current-voltage relationship of the plasma membrane of single CHO cells

The application of electric field pulses to Chinese Hamster Ovary (CHO) cells causes membrane electroporation (MEP). If a voltage or current ramp is applied to the cellular membrane of a single CHO cell, the membrane conductance increases nonlinearly with field strength reaching saturation. In particular, the kinetics of the induced conductance changes represents the data basis for the interpretation in terms of underlying structural changes. The current/voltage characteristic is found to be continuous, but displays occasionally a sharp increase in the conductance. The step-like increases are interpreted to reflect the formation of one (or more) larger pore(s). The analysis of current clamp data yields pores of radius (r(p)) in the range of 2.5< or =r(p)/nm< or =20; the pores of the voltage clamp data are in the range of 2.5< or =r(p)/nm< or =55. The larger pores occur predominantly during hyperpolarising and less frequently during depolarising conditions, respectively. The different kinetics of pore formation in the hyperpolarising condition, where the inward field increases, and the depolarising condition, where the inward field first decreases and then increases in the opposite direction, suggests structural asymmetry with respect to the direction of the electric membrane field. At the required higher voltage, the effect of the resting potential is negligibly small.