ABSENCE OF EFFECTS OF LOW-FREQUENCY, LOW-AMPLITUDE MAGNETIC-FIELDS ONTHE PROPERTIES OF GRAMICIDIN-A CHANNELS

The effects of static and low-frequency magnetic fields on gramicidin A channels have been investigated using bilayer patch clamp recording and a bridge technique capable of detecting 0.3% changes in the conduc tance of glyceryl monooleate membranes containing many channels. In th e bridge technique the conductance was assessed using 10-ms voltage pu lses applied at 10 Hz. Measurements were made for LiCl, KCl, and CsCl using magnetic fields of 50, 100, 500, and 5000 mu T with the frequenc y scanned from 10-200 Hz. The combinations of static and low-frequency fields employed include the ''cyclotron resonance'' conditions at whi ch effects had been predicted to occur. in no case was there any detec table change in conductance when the magnetic fields were applied or c hanged. Potassium currents through single gramicidin channels have bee n recorded for patches in which several channels may be open at once. Fields were applied for 2 min periods interleaved with 2 min controls. Methods have been developed to analyze the multichannel records to re veal the amplitude and duration of the channels together with the freq uency, depth, and apparent period of flickers. No significant differen ces were observed between the control and field-exposed recording peri ods. The peak of the distribution of opening and closing transitions a lways coincided for fields on and off within the resolution, 0.4%, of the recordings. There are at least two types of flicker, one with typi cal period less than 0.1 ms, the other with typical period from 0.3-0. 8 ms. Most of the fatter were not complete closures with the conductan ce during a flicker 15-20% above the level for a full closure.