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 Zeuthenís Zeal

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dranandbhaskar@gmail.com



Number of posts : 53
Age : 38
Location : Christian Medical College, Vellore
Occupation : Associate Professor in Physiology
Educational Qualification : MBBS, MD
Registration date : 2007-01-07

PostSubject: Zeuthenís Zeal   Wed Jun 21, 2017 4:13 pm

Dear Physiologist,

Whenever we think of water transport across biological membranes the first mechanism that comes to our mind is the transport through water permeant molecule aquaporin. Yes indeed, these aquaporins play a major role in transportation of water in the kidney and many other places. However, their presence in the small intestine has not been detected so far. Small intestine is important site of water transport and about 6-7 litres of water may be transported per day. Since aquaporins are not there we must think of other ways of transport. Zeuthen argues in favour of SGLT being the water transporter, which is the most abundant transporter protein in the brush border membrane of the small intestine. He went around to prove it in an ingenious manner. He cultured Xenopus oocytes which do not possess the sodium-glucose cotransporters and inserted the SGLT DNA in to them. Successful insertion led to the expression of SGLT in the membranes of oocytes. He placed the oocytes in media containing sodium and glucose and measured alterations in the volume of oocytes under the microscope. Only the oocytes that expressed SGLT transporters exhibited volume changes in media that were hypotonic or hypertonic, confirming their role in water transport! When phlorizin was included in the media the volume changes were inhibited.

But what I like the most is the simple experiment Zeuthen performed to show that the passive transport of water in the intestine occurs through the SGLT. He took the everted gut sacs of mice and filled them buffered normal saline and incubated them in the same solution at 20 C. When the outside medium was made hypertonic by addition of mannitol, water moved out of the sac and the it lost weight. But no loss occurred when phlorizin was included along with mannitol, clearly indicating a role for SGLT in transport across the intestine.
Everted gut sac technique is an old, simple method that has been used to monitor transports of a variety of substances. Try to establish the method in your laboratory and see if you can verify Zeuthenís hypothesis

J. Prakasa Rao,
Professor of Physiology(Rtd) † † † † † † † † † † † † † † † † † †
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