118 FACTORS AFFECTING CILIARY ACTIVITY 



an independent effect of veratrine on respiration. If veratrine 

 were to increase the rate of ciliary activity, this w^ould of course 

 result in an increase in the rate of respiration. High concentrations 

 of veratrine stop the cilia in the contracted position, and this 

 contracted state can only be broken by the removal of veratrine 

 or interruption of the energy supply. It does not seem very 

 Hkely that an excess of available energy should result in such a 

 continuous contraction, although energy may be necessary for the 

 maintenance of the contraction. 



In veratrine treated muscle, a single stimulus results in a 

 prolonged contraction, apparently because of an increase in the 

 duration of the excitatory state. It seems likely that veratrine acts 

 on the excitation part of the ciliary mechanism, since it affects 

 both frequency and metachronal wave velocity. From recent 

 work on muscle excitation (e.g. Kiebel and Sandow, 1957; 

 Hoffmann, Feigen and Genther, 1962) it appears that the veratrine 

 may be concerned with ionic conditions across the cell membrane ; 

 older work on veratrine and ciliary activity suggests that potassium 

 ions may be important here. 



Several alkaloids, including veratrine, strychnine, aconitine, 

 pilocarpine and emetine have been found to increase the activity 

 of cilia of the frog pharyngeal epithelium, while cocaine, quinine 

 and caffeine depress the activity of these cilia (Ishikawa and 

 Ohzono, 1931). The effects of a number of alkaloids on ciliary 

 activity are summarized in Table 1 1 . 



(b) Digitalis glycosides. The activity of Stentor membranelles 

 is stimulated by digitoxin (Sleigh, 1956a). This glycoside was 

 found to increase both the frequency of beat and the metachronal 

 wave velocity as shown in Fig. 29. The increase in wave velocity was 

 much larger than that in frequency, and showed a maximum at a 

 lower concentration, so that it appears that the effects of digitoxin 

 on wave velocity and frequency may concern different parts of 

 the ciliary mechanism. It has been suggested that digitoxin acts 

 on cardiac muscle by a lowering of the threshold of excitability 

 (Sollman, 1950), and the same explanation could be used here. 

 There is some evidence that glycosides may influence permeability 

 to ions. 



Aiello (1960) has reported that another digitalis preparation, 

 digitalin, reduced both the frequency (by 24 per cent) and the 



