496 



ELECTRICAL SENSES 



A 



B 



m0N^»*^ 



D 



40 uV 



0.1 mV 

 6.6 nA 



0.2 S 



Figure 9 Responses of the short-circuited receptor to small voltage stimuli. Upper trace 

 represents voltage recorded across the ampullary epithelium (lumen-negative up); middle 

 trace, PSP recorded from the afferent nerve bundle (proximal electrode positive recorded 

 up); lower trace, current across the epithelium measured as voltage drop along the canal 

 (as in Figure 8B). (A) A lumen-negative stimulus of about 5 juV produces a clear change in 

 the PSP in the excitatory direction, indicating increased transmitter release. (B) A lumen- 

 positive stimulus of about 15 JJ.V produces a change in the PSP in the inhibitory direction 

 ascribable to decreased release of excitatory transmitter. (C) Clear oscillatory responses 

 produced at the termination of a somewhat larger lumen-positive stimulus lead to oscilla- 

 tory PSPs in the nerve with a receptor peak to nerve peak delay of about 40 ms. (D) A 

 spontaneous oscillation and associated PSP in the nerve similarly delayed. (From Clusin 

 and Bennett 1978a.) 



Recent experiments demonstrate that responsiveness of the basal mem- 

 branes plays a role in the oscillatory behavior of the epithelium (Clusin and 

 Bennett 1978b). As noted above, the series resistance of the basal 

 membranes prevents clamping of the potential across the lumenal membrane 

 in its negative slope region. Changes in the resistance or effective internal 

 potential of the basal membrane would also affect the epithelial activity. In 



