Gum Arabic Enhances Paracellular Transport of Water in Amphibian Everted Small Intestinal Segments.

Gum Arabic (GA) is known for its proabsorbent activity in normal intestine as well as in animal models of diarrhea. The aim of the study was to find the effect of GA on intestinal transport of water and possible route of absorption in frog everted gut sacs. D-Mannitol was used as a marker of paracellular transport to find the route of absorption. Everted gut sacs (n=4,5) were placed in Ringer containing GA (2.5 g/L) with or without D-Mannitol (0.5 g/L), incubated for 1 hour and analysed for change in weights of the sacs and D-Mannitol uptake. There was significant increase in uptake of water and D-Mannitol in the presence of GA compared to controls (P<0.05).Gum Arabic improves water uptake by the intestinal mucosa, possibly by opening the paracellular pathways.

Evidence for functional interaction of plasma membrane electron transport, voltage-dependent anion channel and volume-regulated anion channel in frog aorta.

Frog aortic tissue exhibits plasma membrane electron transport (PMET) owing to its ability to reduce ferricyanide even in the presence of mitochondrial poisons, such as cyanide and azide. Exposure to hypotonic solution (108 mOsmol/ kg H 2 O) enhanced the reduction of ferricyanide in excised aortic tissue of frog. Increment in ferricyanide reductase activity was also brought about by the presence of homocysteine (100 μM dissolved in isotonic frog Ringer solution), a redox active compound and a potent modulator of PMET. Two plasma-membrane-bound channels, the volumeregulated anion channel (VRAC) and the voltage-dependent anion channel (VDAC), are involved in the response to hypotonic stress. The presence of VRAC and VDAC antagonists–tamoxifen, glibenclamide, fl uoxetine and verapamil, and 4,4′-diisothiocyanatostilbene-2,2′-disulphonic acid (DIDS), respectively–inhibited this enhanced activity brought about by either hypotonic stress or homocysteine. The blockers do not affect the ferricyanide reductase activity under isotonic conditions. Taken together, these fi ndings indicate a functional interaction of the three plasma membrane proteins, namely, ferricyanide reductase (PMET), VDAC and VRAC.

Plasma membrane electron transport in frog blood vessels.

In an attempt to see if frog blood vessels possess a plasma membrane electron transport system, the postcaval vein and aorta isolated from Rana tigrina were tested for their ability to reduce ferricyanide, methylene blue, and 2,6- dichloroindophenol. While the dyes remained unchanged, ferricyanide was reduced to ferrocyanide. This reduction was resistant to inhibition by cyanide and azide. Heptane extraction or formalin fi xation of the tissues markedly reduced the capability to reduce ferricyanide. Denuded aortas retained only 30% of the activity of intact tissue. Our results indicate that the amphibian postcaval vein and aorta exhibit plasma membrane electron transport.

Infl uence of dietary calcium content on intestinal permeability in rat.

Background & objectives: Agents that increase the permeability of intestinal epithelium promote the absorption of nutrients by the gut. High calcium concentration in the gut has been shown to enhance passive transport of glucose in the rat intestine. An increase in the permeability of the intestinal epithelium may account for this observation. The present study was aimed at monitoring the permeability of intestine of rats fed high or low calcium diets. Methods: Everted intestinal sacs were used to study transports of substances across the gut. While radioactive and non radioactive calcium isotopes were employed to study the active transport and passive transport of calcium, transport of labelled mannitol was taken as a measure of passive permeability. Results: High calcium diet increased the passive transport of mannitol and calcium while decreasing the active transport of calcium by the everted gut sacs. Interpretation & conclusion: Passive mechanisms are enhanced by high calcium diet, while low calcium diet favours active transport. Calcium in the diet may be affecting intestinal transport.

Inherent rhythmicity and interstitial cells of Cajal in a frog vein.

Interstitial cells of Cajal are responsible for rhythmic contractions of the musculature of the gastrointestinal tract and blood vessels.The existence of these cells and spontaneous rhythmicity were noticed in amphibian vein and the findings are reported in this paper.The postcaval vein was identified in the frog, Rana tigrina and was perfused with amphibian Ringer solution after isolation.Contractile activity was recorded through a tension transducer connected to a polygraph.The isolated postcaval vein showed spontaneous rhythmic activity. Addition of cold Ringer solution decreased, while warm Ringer increased, the rate of contraction. Adrenaline caused inhibition of rhythmic activity at a dosage that increased the rate of isolated sinus venosus.Sections of the postcaval vein,when stained supravitally with methylene blue, showed the presence of interstitial cells of Cajal. Photic stimulation of the vein in the presence of methylene blue led to a significant decrease in the rate of spontaneous beating of the vein.These findings indicate that the postcaval vein of frog is capable of inherent rhythmcity, which is dependent on the interstitial cells of Cajal but is independent of the sinus venosus.