200 



Theories of Secretion 



outer face of these cells averaged — 22 mV (range —15 mV to 

 — 35 mV). On stimulation of the chorda with single shocks the 

 internal negativity increased by 5 to 20 mV after a latency of 0-2 

 to 0-4 second and then returned to the initial potential level in 

 about a second. With repetitive stimulation, the membrane was 

 hyperpolarized by as much as 40 mV although 25 to 35 mV was 

 more usual. With continued stimulation, the potential was main- 

 tained and on cessation of stimulation, the potential returned to 

 the initial value in 2 to 5 seconds (Fig. 10.3). Single shocks to the 

 cervical sympathetic produced no electrical changes but with repe- 

 titive stimulation, a hyperpolarization similar to that produced by 

 chorda stimulation was seen; usually the latency was longer and 

 the magnitude of the potential change smaller than that of the 

 chorda. Similar changes in potential were produced by adrenaline, 

 acetylcholine or pilocarpine. 



In cells near the surface of the gland, a second type of potential 

 (Type II) was also found but the structure in which it is developed 

 has not yet been identified. The resting potential was of the same 

 order as in Type I cells and on stimulating the chorda a hyper- 

 polarization of 15 mV to 20 mV occurred (Fig. 10.40). The latency 

 was brief but the potential rose slowly (only 15 mV/sec as com- 



Fig. 10.4. Cat submaxillary gland. Chorda stimulation indicated by white at 

 lower margin; sympathetic stimulation by line at upper margin, (a) Electrode in 

 unidentified structure producing Type II potentials. 



The first three responses were produced by single shocks to the chorda and the last response 

 by sympathetic stimulation at 25 c/s. Notice the opposite polarities of the responses and 

 compare the time course with the time seen in Fig. 10.3. 



(b) Electrode inserted deep into the gland substance and inside a cell (? duct 

 cell) producing a Type III response. 



Note the high resting potential of this cell and the striking depolarization produced by both 

 chorda and sympathetic stimulation (Lundberg, 1955). 



