Electrophysiology of the Glands 20 1 



pared with 150 mV/sec for Type I cells) and disappeared slowly 

 over 7-10 seconds. However, the most striking difference from 

 Type I is that stimulation of the sympathetic in these cells leads 

 to a depolarization rather than a hyperpolarization ; this also 

 develops and declines slowly. No further exploration of this 

 potential has been carried out. 



When a microelectrode is inserted deep into the gland, a third 

 type of potential may be found (Type III). In these cells the 

 resting potential was —80 mV and chorda stimulation reduced 

 this over a period of a few seconds to only —20 mVto -jomV 

 (Fig. 10.46). At the end of stimulation, the potential returned only 

 very slowly to the initial level. Sympathetic stimulation caused a 

 similar depolarization but with a more drawn-out time course. 

 Lundberg suggests that this potential is derived from the cells of 

 the intralobular ducts, because it is found only in the depths of 

 the gland where the probability of encountering a duct is consider- 

 able, and because the time course of the potential is rather similar 

 to that recorded between a polyethylene catheter inserted back- 

 wards into the gland through the main duct and an electrode on 

 the hilus. This potential has not been found in the sublingual gland 

 where striated duct cells are rather scarce. This evidence can hardly 

 be regarded as proving that Type III potential is produced by 

 striated duct cells, although it is rather suggestive. 



In view of these multiple sources of potential within the gland 

 with their individually varying time courses, polarities and spatial 

 dispositions, it is not really surprising that the external electro- 

 gram should be so complex. Further analysis of the potentials in 

 the submaxillary gland was not pursued because of the difficulties 

 in visualizing the structures and inserting an electrode into the 

 lumen of the acini. Lundberg therefore turned to the sublingual 

 gland in which the tubular arrangement of the acini and their 

 relatively large lumens made further study feasible. 



The acinar cells of the cat sublingual gave a potential identical 

 with the Type I potential of the submaxillary gland — indeed, this 

 is the only type of potential so far detected in this gland. If an 

 electrode was inserted into the acinar lumen this also became 

 more negative to the gland surface during activity ; in the first few 

 seconds the transmembrane potential across the outer face of the 

 cell of a typical cell rose from 31 to 56 mV but that across the 

 inner face (whose resting potential was also about —30 mV) 



