Access

You are not currently logged in.

Access your personal account or get JSTOR access through your library or other institution:

login

Log in to your personal account or through your institution.

If You Use a Screen Reader

This content is available through Read Online (Free) program, which relies on page scans. Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.

Role of Anions and Carbonic Anhydrase in Epithelia [and Discussion]

D. S. Parsons and R. M. Case
Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences
Vol. 299, No. 1097, The Binding and Transport of Anions in Living Tissues (Dec. 1, 1982), pp. 369-381
Published by: Royal Society
Stable URL: http://www.jstor.org/stable/2395782
Page Count: 13
  • Read Online (Free)
  • Cite this Item
Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Role of Anions and Carbonic Anhydrase in Epithelia [and Discussion]
Preview not available

Abstract

The existence of carbonic anhydrase (carbonate dehydratase, EC 4. 2. 1. 1) in blood was suspected and sought because the rates of spontaneous hydration and dehydration of CO2 and carbonic acid were slow compared with the rates of exchange of CO2 with blood. The existence of the enzyme in absorbing and secreting epithelial tissues has, in contrast, often been sought because its presence was required for the operations of theoretical models for the movements of H+ ions or HCO- 3 into or out of epithelial cells. In addition to the HCl-secreting gastric mucosal epithelium, the enzyme was subsequently found in the rumen, in the kidney, especially those of species that produce acid urine, in salivary gland, the liver and biliary duct system, the mucosa of the small intestine, caecum and colon, the choroid plexuses and ciliary body of mammals, in toad urinary bladder and in the Cl--secreting cells of fish gill. The presence of carbonic anhydrase in exocrine pancreas does not seem to be well established. The enzyme, of molecular mass about 30 kDa and containing one zinc atom, exists in three related forms: one of high specific activity and two of low specific activity, one of which is found in red skeletal muscle. Although most, but not all, types of erythrocyte contain both varieties, epithelia usually contain only the high-activity enzyme; however, ox rumen contains large quantities of the low-activity variety as do guinea-pig caecal and colonic mucosae. Salt transport in the intestinal tract is associated with movements of HCO- 3 and of H+ ions, yet although carbon dioxide stimulates solute and fluid transport in the gall bladder and jejunum, and inhibitors of carbonic anhydrase reduce fluid and ion transport across many epithelia, the role of the enzyme in epithelial transport is not clearly understood. Knowledge of the rates of hydration and dehydration of CO2/HCO- 3 in the fraction of the tissue water responsible for the H+-HCO- 3 movements in many secretory epithelia is currently lacking.

Page Thumbnails

  • Thumbnail: Page 
369
    369
  • Thumbnail: Page 
370
    370
  • Thumbnail: Page 
371
    371
  • Thumbnail: Page 
372
    372
  • Thumbnail: Page 
373
    373
  • Thumbnail: Page 
374
    374
  • Thumbnail: Page 
375
    375
  • Thumbnail: Page 
376
    376
  • Thumbnail: Page 
377
    377
  • Thumbnail: Page 
378
    378
  • Thumbnail: Page 
379
    379
  • Thumbnail: Page 
380
    380
  • Thumbnail: Page 
381
    381