AMPULLARY ELECTRORECEPTORS 



4H9 



mV 



-52 -r- 



25 -ir 



B 



mV 



 2 vy\-vw 



— ryw^ 



I 1 late 



SuDDressed 



Figure 5 Active currents of skate electroreceptor epithelium. Figure 5 A shows a family 

 of currents obtained when constant voltage displacements were imposed across an 

 ampulla of standard size. Current flowing inward across the lumenal membranes is de- 

 fined as inward current and shown downward. Voltage displacements that depolarized the 

 lumenal membranes (lumen negative) are defined as positive. The epithelium was held at 

 its resting potential of -12 mV. Lumen-positive stimuli evoked maintained leakage cur- 

 rents. Lumen-negative stimuli between and +88 mV evoked an early inward current fol- 

 lowed by a late outward current. With larger excitatory stimuli, onset of the late outward 

 current was progressively slowed and delayed. At +128 mV, activation of the late out- 

 ward current was suppressed. The currents obtained at +4 and +25 mV shows a secondary 

 peak of inward current. A current vs voltage relation of the data in A is plotted in C. The 

 vertical axis is placed at the holding potential. The leakage current (I L eak^» tne P ea ^ 

 early current (Iearly)' anc * tne l ate outward current (I LATE ) are linearly related to volt- 

 age over broad ranges. The slope resistance during the early current is 64 kf2 within the 

 linear range, while that of the late outward current is 58 k£2. The leakage resistance is 

 203 k£2. The current traces in B are from an electroreceptor whose current — voltage rela- 

 tion (not shown) is similar to that in C. However, the traces in B show several inward cur- 

 rent peaks during small stimuli. These inward current peaks attenuated with progressively 

 larger stimuli. Above 28 mV, only one peak occurred. The holding potential in B was -18 

 mV. The vertical calibration represents 1 [lA in B and 2.4 /JA in A. The horizontal calibra- 

 tion represents 100 ms in B and 220 ms in A. (From Clusin and Bennett 1977b.) 



