Dielectric relaxation studies of ionic processes in lysolecithin-packaged gramicidin channels

Dielectric permitivities have been determined for suspensions of lysolecithin packaged malonyl gramicidin channels over the frequency range of 5 kHz to 900 MHz and under conditions of approximately equimolar concentrations (approximately 10mM) of channels and salts. The salts were lithium chloride, sodium chloride and thallium acetate. A relaxation process unique to the thallium acetate-channel system was observed which on analysis gave rise to a relaxation time at 25 degrees of 120 msec. The permitivity data, as well as a comparison of binding constants, indicate that the relaxation process results from TI+ being bound within the channel and more specifically from an intrachannel ion translocation with a rate constant of approximately 4 x 10(6) sec-1 and with an energy of activation of less than 6.7 kcal/mole. These data compare favorably with data from conductance studies on planar bilayers and with ion and carbon-13 nuclear magnetic studies on the lysolecithin packaged malonyl gramicidin channels which combine to indicate that the relaxation process is due to the jump of the thallium ion across a central barrier.