Publication Database

Modulation of Na and acetate transport by heat shock proteins (Hsp) across the rumen epithelium of sheep (2010)

Art

Hochschulschrift

Autor

Rabbani, Imtiaz (WE 2)

Quelle

Berlin: Mensch und Buch Verlag, 2010 — VIII, 158 Seiten

ISBN: 978-3-86664-861-6

Sprache

Englisch

Verweise

URL (Volltext): https://refubium.fu-berlin.de/handle/fub188/9333

Kontakt

Institut für Veterinär-Physiologie

Oertzenweg 19 b
14163 Berlin
+49 30 838 62600
physiologie@vetmed.fu-berlin.de

Abstract / Zusammenfassung

It has been known from previous studies that the rumen epithelium can adapt, both morphologically and functionally, to changes in diet. This process may take days or weeks however, a daily variation in ruminal pH, predominantly after meals, has also been documented particularly in case of SARA that causes a low ruminal pH (<5.5) for a period of 3-4 hours per day. This diurnal variation in rumen pH and SCFA concentration puts the rumen epithelium in a stressful scenario and demands a rescue mechanism from these short term challenges. It was therefore, the intention of this study to investigate the protective role of heat shock proteins and NHE in the rumen epithelium exposed on the luminal side to changes of pH, SCFA concentration, temperature or osmotic pressure. Using conventional Ussing chamber technique, in vitro, Na and acetate transport across the rumen epithelium were carried out to evaluate these protective effects whereas, concentrate fed animals with ruminal fermentation pattern resembling SARA were used to study the Hsp70 expression in vivo. The following results were obtained: 1\. Characterization of electroneutral Na transport via NHE clearly showed that the isoform NHE3 is mediating electroneutral Na transport. Application of the specific NHE3 blocker S3226 reduced Jms Na and Jnet, which was not different from Isc, indicating that S3226 abolished electroneutral Na transport. 2\. Incubation of isolated rumen epithelium in the Ussing chamber simulating the conditions of SARA i.e. low mucosal pH (6.4-6.0) and/or high SCFA (70-80mmol·l-1) concentrations, increasing temperature or osmotic pressure induced an over- expression of Hsp70. This expression was reduced when the stress conditions exceeded beyond a certain limit. For instance, an increase in temperature (>44°C), SCFA concentration on mucosal buffer (>100mmol·l-1) and decrease in pH on mucosal side (<5.5) reduced Hsp70 expression. 3\. Hsp70 expression could be reduced using a non specific (cycloheximide) or specific inhibitor (triptolide) thus allowing further studies in the presence or absence of Hsp70. Cycloheximide was most effective in a concentration of 3.0 mmol·l-1 while Triptolide was used in a concentration of 100 nmol·l-1. The use of these inhibitors did not affect the Isc or Gt and Na or acetate flux rates under control conditions. 4\. Electroneutral Na as well as acetate transport were significantly higher in the tissues after an over expression of Hsp70. This increase of flux rates was significantly reduced by treatment with cycloheximide or triptolide. 5\. Induction of Hsp expression by low rumen pH and an increase of temperature was confirmed in vivo by feeding concentrates. The tissues of these sheep exhibited higher Na transport rates. It is concluded that the diurnal variation of fermentation pattern are inducing mechanisms which help to protect the tissue against theses challenges. Hps 70 is obviously an integral part of this acute adaptation and enhances NHE3 activity. Extrusion of protons taken up at increasing rates at higher SCFA concentrations and low pH must be considered as a first line of protection against SARA conditions of the rumen fluid. Although the exact mechanism between Hsp expression and NHE3 activity is not clear, Hsp is obviously a protective mechanism in the rumen epithelium too.