Rotating-Field-Induced Rotation and Measurement of the Membrane Capacitance of Single Mesophyll Cells of Avena sativa

Rotation of single cells (mesophyll protoplasts of Avena sativa) induced by a planar, homogeneous rotating field has been observed at a frequency of 20-40 kHz (conductivity of the external mannitol solution 6x 10-5 Ω-1 cm-1). This variation in optimum frequency is largely due to an inverse dependence on cell radius. Rotation direction is opposite to that of the field, and can be reversed at will by reversing the field. The maximum speed of cell spinning was a few cycles per second (and thus always much slower than that of the field) and was proportional to the square of the amplitude of the field. The rotation of a single cell in a rotating field is expected on the basis of the dipole-dipole theory developed by Holzapfel et al., (J. Membrane Biol. 67, 1-14 (1982)), for multi-cell rotation. Measurements of the dependence of optimum applied field frequency on medium conductivity indicate that the dipole is generated by interfacial (Maxwell-Wagner) polarization. The required frequency is a linear function of the conductivity of the external solution. This relationship is used to derive a value for the specific membrane capacitance. Further applications of this technique for cell and membrane research are discussed.