Radio-frequency bioeffects at the membrane level: Separation of thermal and athermal contributions in the characeae

Summary Single cells ofChara braunii andNitella flexilis were placed in a microstrip exposure apparatus and subjected to isolated bursts of radiofrequency irradiation. Their electrical responses were observed both extra- and intracellularly and found to be in accordance with theoretical predictions. In particular, the cell membrane displays rectifier-like behavior up to a cutoff near 10 MHz; this cutoff implies for the principal current carriers a transit time through the membrane of roughly 50 nsec and a mobility within the membrane approximately onefifth that of potassium in free solution. An electrical response of purely thermal origin was also detected; it was separated from the athermal rectifier response on the basis of rise time and frequency dependence. This is believed to be the first instance in which (i) a biological effect of radio-frequency radiation has had its thermal and athermal components clearly separated and (ii) a primary effect of ion transit time through the membrane has been directly detected.