Light scattering and birefringence changes during activity in the electric organ of Electrophorus electricus

Abstract

SUMMARY1. In an attempt to obtain information about structural changes related to electrical activity in Electrophorus electroplates, we have determined the size and time course of the changes in light scattering and in birefringence that occur during and after the discharge of the electric organ.2. The changes in light intensity detected with a photomultiplier were never greater than 0-2 % for a single discharge, and were often much smaller than this, but records with an acceptable ratio of signal to noise could be obtained by signal-averaging techniques.3. A single stimulus led to a decrease, then an increase, and finally another decrease in the light scattered by slices of the main electric organ. These three phases were designated E 1, E 2 and E 3.4. E 1 started at the beginning of the action potential, and its peak was reached at the same time as the completion of repolarization, even when the repolarization was delayed by cooling or hastened by drawing larger currents from the tissue.5. E 2 was proportional to the integral of the current flowing through the slice of electric organ, and may arise from the swelling and shrinking of the tubules that stud the faces of the electroplates. It developed within a millisecond or two of the start of an applied current, and lasted for about 100 msec.6. E 3 was a variable decrease in scattering that lasted for some seconds. 7. A stimulus also led to a transient increase in the birefringence of the electric organ. The optical change followed the change in electrical potential across the innervated faces of the electroplates with a delay of somewhat under 50 pasec.

Analysis of the potential‐dependent changes in optical retardation in the squid giant axon

“…It certainly seems probable that the alterations in the ionic permeability of excitable membranes that are responsible for electrical activity do involve large conformational changes at certain points in the membrane, but none of the experimental evidence supports the idea that these changes have yet been detected optically. One of the most disappointing features of our work, both on nerve and on the electric organ (Cohen et al 1969) was the absence of any component that could easily be linked through similarity of time course or voltage dependence with the sodium or potassium conductance of the membrane. It is true that we have considered here the possibility that there is a small current-dependent component of the retardation response, but it might well be like the current-dependent light scattering response (Cohen et al; in preparation) in arising because of changes in the ionic content of the space between the Schwann cell and the axon membrane, which would affect the form birefringence of the Schwann cell layer; it is thus connected only indirectly with membrane conductance.…”

“…As mentioned in an earlier paper (Cohen et al 1969), preliminary trials were undertaken using membranes of phosphatidylcholine in ndecane; but it soon became clear that the presence of the solvent would greatly complicate interpretation of the results. Further studies of this kind with solvent-free systems would be of considerable interest, although the failure of Berestovsky et al (1970) to obtain any measurable retardation changes in brain phospholipid bilayers indicates that the results may be negative.…”

“…The optical equipment and the chamber in which intact axons were mounted have already been described by Cohen et al (1969. In most of the experiments done at Woods Hole a simplified apparatus was used in which axons were mounted vertically in the chamber designed for light scattering measurements (Cohen, Keynes & Landowne, in preparation), and sheets of Polaroid with their planes of polarization at 450 and 1350 to the vertical were inserted into the chamber on either side of the axon.…”

Changes in axon birefringence during the action potential

“…An account of similar observations on birefringence changes in the electric organ of Electrophoru8 has been given by Cohen, Hille & Keynes (1969).…”

Some effects of n‐pentane on the sodium and potassium currents of the squid giant axon.

“…Haydon, 1975). Moreover, there is some experimental evidence for this inequality (Cohen, Hille & Keynes, 1969). However, although the experimental Tm plots in Fig.…”