212 Theories of Secretion 



change could occur if nerve stimulation facilitated sodium entry 

 into the cell and also potassium loss from the cell, with the latter 

 lagging behind the sodium entry. This can be regarded as a variant 

 of the events that occur during activity in nerve and muscle. After 

 a brief period of stimulation, depolarization will be mainly due to 

 restoration of cell permeabilities to normal, but after longer 

 stimulation reaccumulation of potassium and extrusion of sodium 

 from the cells will be the rate limiting step. Judging from the 

 amount of potassium released in the initial phase of the rest tran- 

 sient, a considerable proportion of the whole duct epithelium must 

 be involved in both the submaxillary and parotid glands of the dog. 

 If the changes suggested above do happen in the duct cells, it is at 

 least plausible that the greater rate of loss of potassium from the 

 inner face of the cells (as compared with the outer face) implies 

 also a greater tendency to absorb sodium from the inner face. This 

 assumption would be supported if a greater depolarization occurred 

 at the inner cell face. Lundberg's measurements of the potential 

 across the duct support this. This differential permeability to 

 sodium might lead to transport from the saliva across the cells 

 and into the blood ; a similar process might also occur for anions. 



Sodium. Burgen, Terroux and Gonder (1959) did not find any 

 striking rest transient for sodium; on the other hand, Brusilow 

 and Cooke (1959) found consistent negative sodium and chloride 

 transients that developed after very brief rest period (10-60 

 seconds). With such short rests they did not find any appreciable 

 potassium transient in the same samples; an unusual feature of 

 these experiments was the high concentrations of sodium (up to 

 135 mEq/1.) and potassium (25 mEq/L), which are greater than 

 those usually found in this secretion. At present no satisfactory 

 correlation can be made between these results and those of See- 

 man (1956) and Burgen, Terroux and Gonder (1959). Over the 

 longer rest periods when a larger potassium transient is developed, 

 there must be concurrent changes in other ions. These have not 

 been investigated fully as yet, but it appears that the potassium 

 transient is accompanied by a corresponding increase in chloride 

 concentration and some decrease in bicarbonate concentration. 

 Much further work is needed, however, to establish the inter- 

 relationships of these four ions during different periods of rest. 



Iodine. The presence of a striking iodide rest transient in dog 

 parotid saliva has been mentioned on page 157. Iodide accumula- 



