C. ADRL\N M. HOGBEN 1 89 



the electrophysiological studies of Rhem and his colleagues have done much to 

 further our understanding. The secreting mucosa of the dog maintains a fairly 

 constant spontaneous potential (serosa positive to mucosa), a mucosal resistance 

 and a short-circuit current which are relatively independent of the rate of H+ 

 secretion (85). Similar observations have been reported for the isolated frog 

 mucosa (8). 



These findings are relevant to an understanding of the role of CI" in HCl 

 formation. As the gastric epithelium maintains an electrical potential adverse 

 to passive diffusion of chloride even when the flow of juice is greatest, the 

 chloride ion is always being actively transported during the secretion of hydro- 

 chloric acid. The actively transported chloride ions form a sum of those equiv- 

 alent to the mucosal electrical current and of those matching actively secreted 

 H"*" ions. As the mucosal short-circuit current is constant and independent of 

 the rate of H+ secretion, variations in H"*" secretion demand corresponding 

 variations in the rate of its equivalent Cl~ secretion. Thus, the active transport 

 of chloride is an integral aspect of HCl secretion. 



It is possible that there is one cell type in the mucosa that has a Cl~ transport 

 system that gives rise to the mucosal current and that there is another cell type 

 which transports simultaneously both H+ and Cl~, but the response of the 

 isolated mucosa to CO2, increasing H"*" at the expense of the mucosal current 

 (46), is not especially favorable to this proposal. 



Rehm has put forward a hypothesis to explain formation of hydrochloric 

 acid linking transport of Cl~ and H+. The active transport of Cl~ creates an 

 emf and this in turn drives an oxidation-reduction reaction creating H+ ions. 

 The principal observation in support of this hypothesis is the effect of potential 

 on the rate of H+ secretion. If the mucosal potential is varied by an external 

 current, secretion of H"*" decreases with a reduction of potential and increases 

 with an augmentation (9, 46, 81). It is worth noting that this physiological 

 observation is the only concrete evidence specifically in favor of a widely held 

 view that the hydrogen ions arise from an oxidation-reduction reaction. A sub- 

 sidiary feature of Rehm's hypothesis is the location of the two processes, Cl~ 

 transport and 11+ formation, in different cell types, though the argument for 

 segregation is not explicitly stated. Because the osmotic shift of water across 

 the exposed surface of the stomach is slow, in contrast to that in the tubules 

 and canaliculi, he locates Cl~ secretion in the parietal cell and H+ elaboration 

 in the surface epithelial cells (86), thereby reversing his previous suggestion (82). 



Another interesting observation is the abrupt fall of the spontaneous po- 

 tential with the onset of secretion — in the dog from 70 to 40 mv (84). If the 

 resting stomach is bathed by o.i m/1. HCl a similar decrease occurs and when 

 the stomach is then stimulated to secrete, there is no further change (87). While 

 several explanations may be entertained, a conductance increase due to the 

 more mobile H"^ ions should be excluded. In the case of the dog, the onset of 



