Calcium in the Intestinal Contents of Rats on Different Calcium Diets

Sernka, Thomas J.; Borle, A. B.

doi:10.3181/00379727-131-34121

Cited by 15 publications

(8 citation statements)

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“…As in prior studies with this method (15,16,24,25,31,32), the solution was adjusted to pH 6.5 with HC1. This corresponds closely to the reported intraluminal pH of both jejunum and ileum although the pH of duodenal content may be lower than this (22). In pilot studies 3H-lactose (as lactose fi-glucose-1 3H.…”

Section: Methodssupporting

confidence: 56%

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Failure of Lactose and Glucose to Influence <i>in vivo </i>Intestinal Calcium Transport in Normal Rats

Urban

Peña

1977

Digestion

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The influence of luminal lactose and glucose on intestinal calcium transport was examined in vivo in normal post-weaned young rats. In situ segments of duodenum, midgut and ileum were perfused through the lumen for 1 h with an isotonic solution of 3.4 mM calcium containing radioactive isotopic ⁴⁵Ca as tracer and additionally either 10 mM lactose or 10 mM glucose or, for the control group, no saccharide. Net absorption was measured by disappearance of luminal calcium; lumen-to-plasma flux was determined from the disappearance of tracer ⁴⁵Ca. This concentration of luminal lactose or glucose had no direct effect on calcium transport under these steady state conditions.

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Section: Methodssupporting

confidence: 56%

“…This study utilized intraluminal solutions containing physiologic concentra tions of calcium (22). Others, that have also directly examined effects of lactose on luminal calcium absorption (6,19,20,26,27), used 7-to 15-fold greater calcium concentrations.…”

Section: Discussionmentioning

confidence: 99%

Failure of Lactose and Glucose to Influence <i>in vivo </i>Intestinal Calcium Transport in Normal Rats

Urban

Peña

1977

Digestion

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“…The free Ca concentration in the duodenal lumen of rats fed about 1 % Ca in the diet is not known, but could be expected to be of the order of 1 mm (cf. Cramer, 1965;Sernka & Borle, 1969). At this level the saturable component of Ca influx into the mucosa would be 90 % of the total (Table 2), or 91 % for uptake by slices (Table 1).…”

Section: Discussionmentioning

confidence: 99%

The kinetics of influx of calcium and strontium into rat intestine in vitro

Papworth¹,

Patrick²

1970

The Journal of Physiology

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SUMMARY1. The role of uptake across the brush border in the intestinal absorption of calcium has been studied by examining the kinetics of influx into slices of rat intestine in vitro. Both mucosal and serosal surfaces were exposed to the medium.2. The rate of influx was accurately defined by a two-component expression comprising a saturable (Michaelis-Menten) term and a second term linear with concentration. Influx across the mucosal surface of closed sacs was similar, and the saturable component for slice influx could be ascribed mainly to transport across the mucosal surface. The half-saturation constant for Ca was near 1 mm. This component was predominant at normal luminal concentrations of free Ca in the duodenum of young rats, but less so in jejunum and ileum and in older rats.3. The same kinetic expression applied to Sr influx, with a half-saturation constant of 2-3 mm, and possibly also to Ba with an even higher value.4. The saturable component of Ca influx was greatly reduced by 2,4: dinitrophenol (DNP); influx was also inhibited by iodoacetate, cyanide and at 00 C. Inhibition commenced soon after exposure of the slices. A high concentration of DNP also caused an increase in the linear component of Ca influx. 5. The kinetics of Ca influx across the mucosal surface agreed closely with the kinetics of steady-state absorption of Ca either across the whole mucosal epithelium in vivo or across the entire intestinal wall in vitro. This agreement supports the hypothesis that Ca entry across the brush border is the rate-limiting step in absorption; such a hypothesis would allow net Ca translocation while preserving a low intracellular concentration of ionic Ca in the mucosal epithelial cells.

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“…The driving force for passive paracellular Ca 2ϩ absorption is the concentration difference between lumen and blood, since the potential difference across all intestinal segments is lumen negative. Thus, although significant after the ingestion of food with a high Ca 2ϩ content (14), passive paracellular flux of Ca 2ϩ may lead to net loss on a Ca 2ϩ -poor diet (31,48).…”

mentioning

confidence: 99%

The Na⁺/H⁺exchanger isoform 3 is required for active paracellular and transcellular Ca²⁺transport across murine cecum

Rievaj

Pan

Cordat

et al. 2013

American Journal of Physiology-Gastrointestinal and Liver Physi

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Intestinal calcium (Ca²⁺) absorption occurs via paracellular and transcellular pathways. Although the transcellular route has been extensively studied, mechanisms mediating paracellular absorption are largely unexplored. Unlike passive diffusion, secondarily active paracellular Ca²⁺ uptake occurs against an electrochemical gradient with water flux providing the driving force. Water movement is dictated by concentration differences that are largely determined by Na⁺ fluxes. Consequently, we hypothesized that Na⁺ absorption mediates Ca²⁺ flux. NHE3 is central to intestinal Na⁺ absorption. NHE3 knockout mice (NHE3-/-) display impaired intestinal Na⁺, water, and Ca²⁺ absorption. However, the mechanism mediating this latter abnormality is not clear. To investigate this, we used Ussing chambers to measure net Ca²⁺ absorption across different segments of wild-type mouse intestine. The cecum was the only segment with net Ca²⁺ absorption. Quantitative RT-PCR measurements revealed cecal expression of all genes implicated in intestinal Ca²⁺ absorption, including NHE3. We therefore employed this segment for further studies. Inhibition of NHE3 with 100 μM 5-(N-ethyl-N-isopropyl) amiloride decreased luminal-to-serosal and increased serosal-to-luminal Ca²⁺ flux. NHE3-/- mice had a >60% decrease in luminal-to-serosal Ca²⁺ flux. Ussing chambers experiments under altered voltage clamps (-25, 0, +25 mV) showed decreased transcellular and secondarily active paracellular Ca²⁺ absorption in NHE3-/- mice relative to wild-type animals. Consistent with this, cecal Trpv6 expression was diminished in NHE3-/- mice. Together these results implicate NHE3 in intestinal Ca(2+) absorption and support the theory that this is, at least partially, due to the role of NHE3 in Na⁺ and water absorption.

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Calcium in the Intestinal Contents of Rats on Different Calcium Diets

Cited by 15 publications

References 1 publication

Failure of Lactose and Glucose to Influence <i>in vivo </i>Intestinal Calcium Transport in Normal Rats

Failure of Lactose and Glucose to Influence <i>in vivo </i>Intestinal Calcium Transport in Normal Rats

The kinetics of influx of calcium and strontium into rat intestine in vitro

The Na⁺/H⁺exchanger isoform 3 is required for active paracellular and transcellular Ca²⁺transport across murine cecum

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Calcium in the Intestinal Contents of Rats on Different Calcium Diets

Cited by 15 publications

References 1 publication

Failure of Lactose and Glucose to Influence <i>in vivo </i>Intestinal Calcium Transport in Normal Rats

Failure of Lactose and Glucose to Influence <i>in vivo </i>Intestinal Calcium Transport in Normal Rats

The kinetics of influx of calcium and strontium into rat intestine in vitro

The Na+/H+exchanger isoform 3 is required for active paracellular and transcellular Ca2+transport across murine cecum

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The Na⁺/H⁺exchanger isoform 3 is required for active paracellular and transcellular Ca²⁺transport across murine cecum