ELECTRIC CURRENTS 



91 



found to accompany reversal of ciliary beating in Paramecium 

 (Yamaguchi, 1960). 



Naitoh (1958) has taken the investigations on Opalina further 

 by using an intracellular electrode to apply an electric current. 

 The effect of current intensity and direction on the membrane 

 resistance is shown in Fig. 23. Membrane resistance is constant 

 for inward current (i.e. internal electrode negative), but decreased 

 to about one-tenth with an outward current of 4 x 10~^ A or more. 

 In this example, the voltage applied when the current was zero 

 was about 12 mV acting in opposition to the cell membrane 

 potential; the average value at 13-7 to 16-2°C was 16 mV. 



-3 -2 -1 



8 



12 3 4 5 6 7 

 Current in 10-'-* Amp. 

 Fig. 23 . The change in membrane resistance of the whole body 

 of Opalina induced by application of direct current. Negative cur- 

 rent values indicate inward current flow (i.e. the internal electrode 

 was negative and the applied voltage greater than the membrane 

 potential). Results measured at 15-5°C (from Naitoh, 1958). 



Membrane resistance is not uniform over the whole of the cell 

 surface, and topographical differences in ciliary reversal response 

 may result from this. 



Direct current stimulation with such a microelectrode, passing 

 more than 2 x 10~^^ A across the membrane in an outward 

 direction, induced a change in direction of the effective stroke. If 

 the current intensity is increased, the degree of change in direction 

 is increased until the beat is completely reversed. When such a 

 stimulating current is switched off, the beat in the normal 

 direction is temporarily augmented. With inward current the 



