206 Theories of Secretion 



for the resting potential of these cells, their entry into the cell must 

 be almost exclusively by an active process and very nearly inde- 

 pendent of the external concentration. Since the sodium and potas- 

 sium concentrations in these cells are not very different from those 

 found in muscle or nerve, these are presumably maintained by 

 cation "pumps" acting more or less independently of any anion 

 uptake. The dependence of the resting potential on the external 

 ion concentrations should be studied directly in view of the unusual 

 features present. 



It is particularly difficult to understand what connection there 

 is between hyperpolarization of the outer face of the acinar cells 

 and the secretory process. Neither the electrochemical potential of 

 the ions within the cell with respect to the fluid in the acinar 

 lumen nor the conductivity of the inner membrane change much. 

 Of course, the nature of the potential across the inner cell mem- 

 brane will remain puzzling as long as the composition of the acinar 

 lumenal fluid is unknown, on the other hand, this method has 

 provided unequivocal proof of the convergence of parasympathetic 

 and sympathetic nerves on to the same cell ; this must not lead us to 

 assume, however, that because similar hyperpolarizations are pro- 

 duced by the two nerves, their effects on the secretion of either 

 electrolytes or non-electrolytes is identical. The possible relation- 

 ship of the Type III potential to permeability changes in the ducts 

 during stimulation is discussed below. It is obviously of great 

 importance that the membrane conductivity changes occurring 

 during these potentials, as well as the time course of the potential 

 over a longer period of stimulation, should be examined further. 



SALIVARY REST TRANSIENTS 



Potassium. It was first noted by Kesztyiis and Martin (1937) 

 that the concentration of potassium in the saliva secreted at the 

 beginning of a period of stimulation was greater than the con- 

 centration found after secretion had continued for a minute or 

 two. This phenomenon has subsequently been investigated in 

 some detail (Burgen, 19560; Burgen and Seeman, 1958; Burgen, 

 Terroux and Gonder, 1959; Seeman, 1956). After a rest period 

 of half an hour or more has been allowed since the last period 

 of stimulation, the first saliva secreted on stimulation contains 

 up to 60 mEq/1. of potassium. With continued stimulation, 

 this concentration gradually falls over a period of 2-3 minutes 



