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The most obvious effect is the paramecia turn and reverse swim perpendicular to the field, this occurs at all frequencies. All frequencies seem to cause ciliary augmentation which is reflected in enhanced motion either reverse swimming speed and/ or greater rolling rate and /or greater apparent yawing motion. The yawing motion may increase with increasing frequency. Above 2300 Hz they do not respond and swim as normal.
I am struggling to explain these results however some speculative comments follow-
1) It has been reported that Paramecia will align and swim perpendicular to an intense static magnetic field and that this effect is probably due to the diamagnetism of the cells and as such is a non-physiological response. This probably not significant to my set up!
2) The ciliary augmentation and swimming direction reversal perhaps has the same basic mechanism as that seen with DC fields i.e., raised intracellular Calcium ion levels caused by voltage sensitive ion channels.
3) With DC the polarisation caused by the field is along the anterior/posterior axis of the Paramecium. This ultimately helps produces the differential ciliary response and its turning to swim towards the cathode. The 'barrel rolling of the cell will not significantly affect the anterior/dorsal polarization?
4) With an AC field presumably the polarisation is reversed every cycle? As the cell corkscrew's and alters its alignment to the field there might be transient and differential polarisation across its width (dorsal/ventral axis). This in turn might produce transient and differential amounts of ciliary augmentation. This will continue until the cell is perpendicular to the field. The ‘barrel rolling’ will then serve to 'even out' the augmentation around its circumference? This coupled with the ciliary augmentation and reversal might produce the observed swimming behaviour.
5) Above 2,300 Hz does the frequency of the field changes exceed the response time of the augmentation mechanism? Hence the lack of response.
6) The increases ‘yawing’ action with frequency. Could this be due to an interaction between the applied field frequency, the rate of role of the cell, the frequency of the cells cilia’s metachronal waves. At some point in the movement cycle do they reinforce the augmentation leading to the enhanced yawing? Very speculative!
All this might well be wide of the mark. I would very much welcome other opinions, and perhaps other people might want to create their own versions of the apparatus and report their findings? As time allows, I will continue with my investigations in this interesting area.
Martin