C. ADRIAN M. HOGBEN 



193 



frog mucosa is exposed to a higher concentration (10 mM/1.), the spontaneous 

 H"*" secretion is depressed to only about 60% of control, while the spontaneous 

 potential drops over a 30-minute period to values 25% or less of control (fig. 

 lb). The mucosal short-circuit current, like the spontaneous potential, is much 

 more strikingly inhibited than is H+ secretion. The eflfect of this carbonic an- 

 hydrase inhibitor on these two manifestations of chloride transport and upon 

 the measured chloride fluxes is completely reversible even after 6 hours of ex- 





SECRETORY GAS 

 I I 100 % O2 

 5 % COa 



hr-' 

 cm-* 



SECRETORY GAS 

 ES^ 100 % O2. 

 ■■ s % COo 



UMM 



NUTRIENT SOLUTION- 



mV 20 



NUTRIENT SOLUTION- 



HCOa-Free Saline 



100 % 02 



Fig. Id (left). The bar diagram indicates the rate of H^ secretion, the ordinate; of the 

 two halves (A & B) of a mucosa which were alternately exposed to 5% CO2 for 6 consecu- 

 tive hour periods, given as the abscissa. The curves below follow the mean spontaneous po- 

 tential in mv, the ordinate, for the corresponding 6 hour periods. 



Fig. lb [right). Effect of 'Diamox' on hydrogen ion secretion and spontaneous potential of 

 two halves of a mucosa (A & B) during 6 hour periods, with complete recovery of the potential 

 after removal of the inhibitor. The bar diagram and curves are based on the convention used 

 in figure la. The incomplete bars on the extreme left and right indicate control H"*" secretion 

 in the absence of Diamox. The H^ increase elicited by exposure of the secretory surface to 

 5% CO2 is less when the nutrient surface is continuously exposed to CO2 and HCOs". The 

 portions of the potential curves corresponding to these control values of H+ secretion indicate 

 the extent of the inhibition and recovery after 6 hours of exposure to the carbonic anhydrase 

 inhibitor. 



posure to the drug. Higher concentrations of Diamox have not been studied as 

 10 mM/1. is close to the limit of solubility. 



In a series of experiments detailed in table 2, the responses of the chloride 

 fluxes of the isolated frog mucosa to 'Diamox' were measured. This carbonic 

 anhydrase inhibitor modifies the chloride flux in the direction of its active trans- 

 port, decreasing the net transport by some 60%. Interestingly enough, the 

 inhibition of net chloride transport, short-circuit current and spontaneous 

 potential could, in large measure, be reversed by exposing the mucosal surface 

 to bicarbonate. In the absence of Diamox, introduction of bicarbonate into 



