Rhythmical Impedance Changes in the Egg of the Trout. III

Abstract

ABSTRACT Accelerated cine-photographs show that the unfertilized trout egg exhibits rhythmical movements within its chorion after immersion in tap water. The movement can be described as a periodic axial perturbation or ‘precession’, similar to that which takes place in a slowing-down top. The egg does not, however, spin at the same time. The frequency of the motion is about 3·4 min. at 16·8° C. There is a strict correlation between the frequency of the egg precession and the frequency of the impedance changes that are observed when the egg is placed in a conductivity cell in an alternating current bridge. The impedance changes exhibit a characteristic ‘impedance pattern’, the frequency of which is identical with that of the precession. The oscillations are neither initiated nor affected by the measuring current. The question as to whether the electrical changes are entirely caused by the dielectric heterogeneity and precession of the egg, or whether they are partly due to changes in the vitelline membrane, associated with the egg movements, is discussed. The former is the simpler hypothesis, and there is some evidence in support of this interpretation from impedance measurements made with the electrodes in different planes relative to the egg. It was difficult to reach a firm decision on this point because the electrical method of recording the changes is more sensitive and accurate than existing optical methods. Examination of the fine structure of the impedance cycle, by means of the ellipse technique and enlarged time-impedance loci at particular frequencies, shows that there is a very small resistance change associated with the impedance oscillations, which is not in phase with the capacitance change. The possibility of these resistance changes being due to variations in the position of the egg relative to the measuring electrodes; combined with small deviations from Maxwell’s formula, or to resistive heterogeneity in the vitelline membrane, or to changes in the resistance of the vitelline membrane, is discussed. The variation of frequency with temperature has been investigated. In one typical run, the temperature characteristic was 15,200 which corresponds to a Q10 of 2·47. The average value of the temperature characteristic for the whole season was 16,200. There are no obvious ‘breaks’ in the curve relating log velocity to the reciprocal of the absolute temperature; the curve obeys Arrhenius’s equation except at temperatures above 18° C., when irreversible changes tend to set in. There is no very convincing reason for associating this temperature characteristic with developmental processes, particularly as measurements are made on unfertilized eggs. On the other hand, the possibility of all unfertilized eggs undergoing abortive partheno-genetic activation on immersion in tap or stream water is discussed. Sodium cyanide (M/300, M/500, M/100 in tap water, pH adjusted) reversibly reduces the frequency and amplitude of the impedance changes, which suggests that cytochrome is concerned in the metabolic system responsible for the egg movements. The frequency is more sensitive to cyanide than the amplitude. There are indications that this compound has some effect on the electrical properties of the vitelline membrane, but this has not been systematically examined. Sodium azide, which has no effect at pH 7·4, cannot be used at pH 6·5 because this concentration of H+ in the external medium has a marked, though not permanent, effect on the egg movements and impedance changes. Neither phlorizin (M/100, M/200, M/500 in tap water, pH not adjusted), nor sodium fluoride (M/25, pH not adjusted) have any effect on the egg movements or the impedance cycle. This suggests that the energy for these changes is not glycolytic in origin; but there is a possibility that the molecules of these inhibitors do not penetrate the vitelline membrane. The action of the inhibitors does not as yet permit any comparison to be made with ciliary or amoeboid movement, or with muscular contraction, as the experiments do not enable a distinction to be made between the utilization of oxygen in the breakdown phase or the resynthesis phase of the metabolic cycle. The following substances have no effect on egg movements or impedance changes: Laboratory-distilled water. There is a possibility that distilled water affects the properties of the vitelline membrane, in the sense that some exosmosis of electrolytes occurs when the egg is in the medium. This has not been systematically examined as it has no direct bearing on the egg oscillations.M/25-CaCl2 in tap water.0·001 M-chloretone in tap water.There is no appreciable periodic change in egg volume.