Intestinal bicarbonate secretion in Amphiuma measured by pH stat in vitro: relationship with metabolism and transport of sodium and chloride ions.

Abstract

SUMMARY1. Isolated Amphiuma small intestine exposed on both surfaces to buffered or unbuffered media generated gradients of pH under short-circuited conditions consistent with secretion of HCO3-.2. When unbuffered mucosal medium was maintained at pH 7-4 by addition of acid, alkalinization of the mucosal medium occurred at a rate of 1-2 #tequiv/hr cm2 under short-circuit conditions (Is,) and was reduced by anoxia, acetazolamide or removal of CO2. 3. The rate of HCO3-secretion (JHCO3-) was reduced at a mucosal pH above or below 7-4 and was proportional to serosal HCO3-.4. JHCO3 was reduced in Na+-free (choline) and Cl--free (SO42-) media and after exposure to the stilbene SITS.5. The difference JHCO3 -lS was consistent with net Cl-absorption.6. The tissue resistance (Rt) was elevated upon exposure to serosal HCO3-and lowered by mucosal HCO3-.7. The intestinal mucosa exhibited carbonic anhydrase activity that was sensitive to ethoxazolamide.8. It is concluded that HCO3-secretion is active, influenced by intracellular carbonic anhydrase activity and coupled to Cl-and possibly Na+ absorption.

The effect of theophylline on intestinal bicarbonate transport measured by pH stat in Amphiuma.

“…As seen in Fig. 2 JHC03 , which declines slowly under these conditions (Imon & White, 1981) was unaffected by theophylline. In contrast the ISC was rapidly increased before declining to a stable value.…”

“…HCO3-secretion, but not HC03-absorption is dependent on media Cl- (compare Tables 1 and 3) and media Na+ (Imon & White, 1981 and unpublished observations). These observations and the agreement between the reported residual fluxes and the calculated net HCO3-flux provide evidence the unidirectional fluxes are indeed independent.…”

“…These observations pointed to active Cl-absorption linked to HCO3-secretion in the urodele intestine. The inhibition of both processes by the serosal application of the stilbene SITS (White, 1980;Imon & White, 1981) Cl--HCO3-exchange mechanism like that in erythrocytes (Cabantchik & Rothstein, 1972). If the anion fluxes are linked in this way then inhibition of HCO3--dependent Cl-absorption by theophylline ( Leitch & Burrows, 1968;Norris et al 1969;Moore et al 1971) which is reduced by administration of acetazolamide (Leitch, Iwert & Burrows, 1966;Norris et al 1969).…”

“…We have recently adapted the pH stat technique for this purpose after it became clear that HCO3-transport in the urodele intestine is quite large, even capable of generating pH gradients across the mucosa (Imon & White, 1981). In the present study the effect of theophylline on the absorptive and secretary flux of HCO3-is examined.…”

Modes of Cl− transport across the mucosal and serosal membranes of urodele intestinal cells

“…This finding is indicative of the presence of a saturable process underlying C1 transport from the cell into the serosal medium. Considerable evidence has been developed in recent years for the presence of an anion exchange process in the serosal membrane of Amphiuma intestinal cells [13,31,34]. For example, the value of all is normal when HCO3 is absent from the bathing medium [27], yet CI-absorption from the cell into the serosal medium is completely blocked [31].…”