Salivary Rest Transients 2 1 1 



the rest period. If the potassium were indeed stored in the lumen 

 we would expect that the transient would be independent of the 

 rate of nerve stimulation and would not be present when the rate 

 of stimulation was changed. All these phenomena, however, can 

 be accounted for quite satisfactorily if the source of the potassium 

 in the first phase of the rest transient is the intracellular potassium 

 of the duct cells which is discharged partly into the saliva and partly 

 into the periductal blood. The loss across both faces of the cell 

 would then be dependent on the rate of stimulation. The blood and 

 saliva transients would be proportional to each other and the effect 

 of raising the rate of stimulation without a rest period would also 

 be adequately accounted for. Persumably, just as the whole gland 

 potassium content reaches a different steady state depending on the 

 intensity of stimulation, so the duct cell potassium might be simi- 

 larly affected. The duration of the initial phase of the rest transient 

 would therefore be dictated by the time taken for the duct cell 

 potassium to reach a new steady state with its surroundings. The 

 time taken for the rest transient to be restored after a period of 

 stimulation would correspond to the time taken for the duct cells 

 to recover their intracellular potassium concentration. The relative 

 rapidity with which this occurs is another argument in favour of 

 believing that there is a high rate of blood perfusion through the 

 periductal capillaries. 



Can we conclude that the late phase of the potassium transient 

 is also of duct origin? This seems improbable for the following 

 reasons: (a) potassium loss from the gland during stimulation is 

 larger than can be accounted for by loss of all the duct potassium ; 

 (b) following intra-arterial injection of K 42 (see page 216) the out- 

 flow curve shows a prolonged course without a correspondingly 

 slow rise in activity; (c) in unloading type experiments with K 42 

 after the initial transient, the specific activity of the saliva potas- 

 sium follows that of the whole gland potassium although it is 

 always somewhat lower. 



These deductions about the behaviour of the duct cells during 

 stimulation may be correlated with the changes in the Type III 

 potential described by Lundberg. The resting potential in these 

 cells is high (about -80 mV), therefore they probably have a high 

 intracellular potassium. On stimulation, a striking depolarization 

 to about —20 mV occurs over a few seconds. On cessation of 

 stimulation, the potential is restored quite slowly. Such a potential 



