916 



7. MERCURIALS 



Intestinal Transport 



The transports of Na+, water, and glucose across the rat intestine are 

 inhibited by Hg++ (Clarkson and Cross, 1961). The transintestinal electric 

 potential is dependent on the Na+ transport and the ionic permeabilities 

 of the lumenal membranes. Hg++ 0.01-1 mM causes a rapid brief elevation 

 of the potential which is followed by a fall, the rapidity of which is deter- 

 mined by the Hg++ concentration. There are two phases in the response: 

 (1) an immediate loss of K+ and phosphate from the intestinal wall and a 

 marked inhibition of glucose uptake, and (2) a delayed (occurring after 

 20 min or longer) inhibition of transintestinal transport of Na+, water, and 



4 



0.3 



0.2 



0.1 



0.1 



0.2 



03 0.4 0.5 0.6 0.7 0.8 



Fig. 7-43. Effects of inhibitors on the respiration and acid secretion 



of mouse gastric mucosa stimulated by carbachol. (From Davenport 



and Chavre, 1956.) 



glucose, with a suppression of lactate formation. The uptake kinetics of 

 Hg++ show two phases, a fast component dominant during the initial 20- 

 30 min of exposure (k^ = 0.0032 min'^) and a slower component (^2 — 

 0.0017 min-^). It was pointed out that the system is so complex that it is 

 difficult to interpret the uptake data, but possibly there is some correlation 

 with the initial and delayed responses discussed above. Analysis showed 

 that the potential changes are produced when certain quantities of Hg++ 

 are bound to the intestine; i.e., when different concentrations of Hg++ are 

 applied to the intestine, the potential changes occur at different rates which 

 are related to the uptake rates. Since the transports and potential are de- 



