Chloride, Gluconate, Sulfate, and Short-Chain Fatty Acids Affect Calcium Flux Rates Across the Sheep Forestomach Epithelium

Abstract

In ruminants, more than 50% of overall gastrointestinal Ca absorption can occur preintestinally, and the anions of orally applied Ca salts are thought to play an important role in stimulating ruminal Ca absorption. This assumption is based mainly on ion-exchange studies that have used gluconate as the control anion, which may bind Ca2+ ions and interfere with treatment effects. In the present study, we investigated the distinct effects of different anions on Ca absorption across the sheep rumen and on the concentration of free Ca2+ ions ([Ca2+]ion). We showed that gluconate, sulfate, and short-chain fatty acids (SCFA) remarkably reduced [Ca2+]ion in buffer solutions. Nevertheless, increasing the Cl or SCFA concentration by 60 mM stimulated net ruminal Ca absorption 5- to 7-fold, but these effects could be antagonized by gluconate. Therefore, ion-exchange experiments must be (re)evaluated very carefully, because changes in [Ca2+]ion in the presence of gluconate, sulfate, or SCFA not only might entail an underestimation of Ca flux rates, but also might have effects on other cellular pathways that are Ca2+ dependent. Concerning the optimal Ca supply for dairy cows, the present study suggests that CaCl2 formulations and Ca salts of the SCFA stimulate Ca absorption across the rumen wall and are beneficial in preventing or correcting a Ca deficiency.

Vitamin D receptor distribution in intestines of domesticated sheep Ovis ammon f. aries

“…Via vitamin D receptor mediated genomic mechanisms calcitriol should provide a calcium absorbing machinery of maximum capacity, i.e., high contents of calbindin-D9k (Haussler et al, 1995;Zhu et al, 1998;Walters et al, 1999;Christakos et al, 2003;Lee et al, 2003;Yamagishi et al, 2006), of its own receptor (Horst et al, 1990;Haussler et al, 1995;Chen et al, 2006;Yamagishi et al, 2006) and of Ca-transporting ATPase (Haussler et al, 1995;Zhu et al, 1998;Yamagishi et al, 2006) as already confirmed for some of these parameters in several studies (Feldman et al, 1979;Clemens et al, 1988;Lointier et al, 1991;Barley et al, 1999;Yamamoto et al, 1999;Barley et al, 2001;Yamagishi et al, 2002). Finally, the quantitative role of intestinal Ca absorption in domestic ruminants is discussed controversially because it was shown that the rumen is an important site for active and calbindin-9kD-independent Ca absorption in sheep (Schröder et al, 1997(Schröder et al, , 1999(Schröder et al, , 2001Wilkens, 2006;Leonhard-Marek et al, 2007;Schröder and Breves, 2007). In the large intestine, stem cells are located at the base of the crypts and all daughter cells migrate upwards during differentiation (Potten and Grant, 1998;Backus et al, 2002;Marshman et al, 2002;Pinto and Clevers, 2005).…”

Gene expression in the digestive tissues of ruminants and their relationships with feeding and digestive processes

“…Similarly, the facilitated transport of Ca 21 from the gastrointestinal lumen to the blood is critical to meet the increase in calcium demands of early lactation in ruminants, particularly dairy cattle, which exhibit a high incidence of hypocalcemia or 'milk fever ' half of the Ca 21 uptake in ruminants and that absorption in the rumen increases with increased calcium intake, and is stimulated by SCFA in the diet (Leonhard-Marek et al, 2007). In addition, the calcium-binding protein, calbindin-D 9k (CaBP-9k) is one of the multiple calcium-binding proteins that facilitates calcium absorption in the intestine of mammals (Choi and Jeung, 2008) and its expression in GIT of dairy cattle of various ages, parities and degrees of clinical disease was evaluated by Yamagishi et al (2002) by Northern blotting.…”

Transport of cations and anions across forestomach epithelia: conclusions from in vitro studies

“…When Ca 21 intake rises to 8 g/day in sheep or to 120 g/day in cattle, absorption of Ca 21 is shifted to preintestinal regions (Grace et al, 1974;Khorasani et al, 1997;Schrö der and Breves, 2006 (Hö ller et al, 1988a and1988b;Schrö der et al, 1997;Wadhwa and Care, 2000). Active ruminal Ca 21 absorption can be increased by concentrate feeding (Uppal et al, 2003), in the presence of SCFAs (Schrö der et al, 1997 andWadhwa and Care, 2000;Uppal et al, 2003, LeonhardMarek et al, 2007a or by increasing the amounts of luminal chloride (Leonhard-Marek et al, 2007a), whereas sulfate ions seem to have stimulatory and depressing effects with no net change of Ca flux rates in vitro (Leonhard-Marek et al, 2007b). An increased absorption of undissociated SCFA will provide protons to the cell interior, while the ruminal uptake of SCFA 2 or Cl 2 via anion exchange mechansims is accompanied by a secretion of bicarbonate (Gä bel et al, 1991a) and an increase in surface pH (Leonhard-Marek et al, 2006).…”

“…This context was used repeatedly to explain the stimulatory effects of Cl 2 on the electroneutral absorption of Na 1 , Mg 21 and Ca 21 across rumen epithelium Leonhard et al, 1991;Sehested et al, 1996;Leonhard-Marek et al, 2007a). Additional effects of Cl 2 on electrogenic cation absorption raised the hypothesis that apical Cl 2 channels might mediate a Cl 2 dependent change in membrane potential and thereby increase the electric driving force for cation uptake (Leonhard-Marek and Schrö der, 2002;Leonhard-Marek et al, 2006).…”