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Electrogenic proton secretion in the Hindgut of the desert locust, Schistocerca gregaria (1992)

Thomson, Robert B. ; Phillips, John E.

Springer

The journal of membrane biology 125 (1992), S. 133-154

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ISSN: 1432-1424

Keywords: pH ; carbon dioxide ; bicarbonate ; proton secretion ; excretion ; locust

Source: Springer Online Journal Archives 1860-2000

Topics: Biology , Chemistry and Pharmacology

Notes: Summary The cellular mechanisms responsible for rectal acidification in the desert locust, Schistocerca gregaria, were investigated in isolated recta mounted as flat sheets in modified Ussing chambers. Previous studies conducted in the nominal absence of exogenous CO2 and HCO 3 − suggested that the acidification was due to a proton-secretory rather than bicarbonate-reabsorptive mechanism (Thomson, R.B., Speight, J.D., Phillips, J.E. 1988. J. Insect Physiol. 34:829–837). This conclusion was confirmed in the present study by demonstrating that metabolic CO2 could not contribute sufficient HCO 3 − to the lumen to account for the rates of rectal acidification observed under the nominally CO2/ HCO 3 − -free conditions used in these investigations. Rates of luminal acidification (J H +) were completely unaffected by changes in contraluminal pH, but could be progressively reduced (and eventually abolished) by imposition of either transepithelial pH gradients (lumen acid) or transepithelial electrical gradients (lumen positive). Under short-circuit current conditions, the bulk of J H + was not dependent on Na+, K+, Cl−,Mg2+, or Ca2+ and was due to a primary electrogenic proton translocating mechanism located on the apical membrane. A small component (10–16%) of J H + measured under these conditions could be attributed to an apical amiloride-inhibitable Na+/H+ exchange mechanism.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00233353

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Mini-review: Islet transplantation to create a bioartificial pancreas (1994)

Mikos, Antonios G. ; Papadaki, Maria G. ; Kouvroukoglou, Stylianos ; [et al.]

New York, NY [u.a.] : Wiley-Blackwell

Biotechnology and Bioengineering 43 (1994), S. 673-677

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ISSN: 0006-3592

Keywords: islet transplantation ; bioartificial pancreas ; immunoisolation ; extravascular devices ; macroencapsulation ; microencapsulation ; Chemistry ; Biochemistry and Biotechnology

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology

Notes: Donor scarcity precludes the use of pancreatic transplantation to treat type I diabetes. Xenogeneic islet transplantation offers the possibility of overcoming this problem; however, it entails the use of immunoisolation devices to prevent immune rejection of the transplanted islets. These devices consist of a semipermeable membrane, which surrounds the islets and isolates them from the host's immune system, while allowing the passage of insulin and essential nutrients, including glucose. Problems associated with proposed device designs include diffusion limitations, biocompatibility, device retrieval in the event of failure, and mechanical integrity. Microencapsulation appears to be the most promising system of immunoisolation, however, the design of a device suitable for human clinical use remains a challenge. © 1994 John Wiley & Sons, Inc.

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