WEAK NONLINEARITY OF CURRENT-VOLTAGE CHARACTERISTICS OF GRAMICIDIN-D CHANNELS - EXPERIMENT, THEORY AND APPLICATION TO THE STUDY OF TRANSMEMBRANE TRANSMISSION OF INFORMATION

A new, sensitive method of measurement of current-voltage characterist ics (CVC) of the type i(U) similar to U(1 + beta U-2) was applied to s tudy ionic channels formed by gramicidin D in bilayer lipid membranes (BLM). The values of the nonlinearity coefficient beta of the CVC of m embranes modified by gramicidin D depended on electrolyte concentratio n, C, and expressed the weak nonlinearity of the CVC. In symmetric ele ctrolyte conditions, the coefficient beta(s) increased with the increa sing electrolyte concentration from -17 V-2 at 0.03 mol/l KCl to 8 V-2 at 3 mol/l KCl. In asymmetric electrolyte conditions (different elect rolyte concentrations at the two sides of the BLM) the coefficient bet a(A) also increased with increasing C. A theory is proposed describing the weak nonlinearity of CVC of ionic channels based on electrodiffus ion model. This theory assumes that the electrochemical potential mu(x ) of an ion within the ion channel depends on the coordinate s along t he channel axis. According to the proposed model, CVC nonlinearity is mainly determined by the ends of the ion channel. We showed that the s tructure of gramicidin D ionic channel is sensitive to the concentrati on of ions, and in fact changes at one end of the channel influence th e parameters of the other channel end.