EXCITATION BY H YPERPOL ARIZl NG POTENTIALS 



335 



]5mV 

 isec 





_i ^ ^L 



100 



mV 60 

 20 



-50- 



-30 



-50 



-rn- 



l//g odr. 0,1/^9 ach 



.A 



Isec ^J\^ 



0,5/^q pilocor 



120 

 100 



Fig. 8. Different types of electrical activity in cat salivary gland cells. Depolariza- 

 tion shown as downward deflection in these records, a. Type I cells produce 

 hyperpolarizing p.s.p.'s which are graded with strength of the stimulus. Single 

 shocks to chorda tympani evoke p.s.p.'s which last about 1 sec. b. Type I cells 

 produce only hyperpolarizing p.s.p.'s to excitation of the sympathetic (upper 

 signal) or parasympathetic {lower signal) nerves. However, the latencies and 

 magnitudes of the p.s.p.'s differ somewhat, c. Type II cells develop hyper- 

 polarizing p.s.p.'s on stimulating the chorda tympani and depolarizing p.s.p.'s 

 through their sympathetic innervation, d. Type III cells (which may be myo- 

 epithelial elements of the ducts) respond only with depolarizing p.s.p.'s to 

 parasympathetic {above) or sympathetic (below) stimulation. The resting poten- 

 tial, about — 80 mV, is large in comparison with that of Type I or II cells and 

 resembles that of muscle fibers, e. Type I cells respond with hyperpolarization 

 to epinephrine, acetylcholine and pilocarpine. (From Lundberg, 1955.) f. The 

 hyperpolarizing p.s.p. of the gland cell is remarkably insensitive to changes of 

 the membrane potential. The resting potential was 30 mV. (From Lundberg, 



1956.) 



23 



