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PubMed2002

Postnatal development of parvalbumin and calbindin D-28k immunoreactivities in the canine anterior cingulate cortex: transient expression in layer V pyramidal cells.

We have examined the ontogeny of parvalbumin (PV) and calbindin D-28k (CB) immunoreactivities in the canine anterior cingulate cortex (ACC) from the day of birth (P0) through P180. At P7, PV immunoreactivity first appeared in layer VI multipolar cells. The PV immunoreactivity in GABAergic nonpyramidal cells appeared to follow an inside-out gradient of radial emergence. Although immunoreaction was limited mainly to the developing nonpyramidal cells, pyramid-like PV immunoreactive cells were transitorily observed in layer V from P14 to P90. The developmental pattern of CB immunoreactivity differed from that of PV immunoreactivity. CB immunoreactivity first developed in layer V pyramidal cells from P0, which continued through P90. CB immunoreactive nonpyramidal cells were located in the infragranular layers and white matter at P0 and matured in both the supragranular and infragranular layers without clear inside-out gradient. This developmental study revealed the comparable belated expression of PV immunoreactivity and the transient expression of both calcium-binding proteins in layer V pyramidal cells. These results suggest that the transient expression of calcium-binding proteins in layer V pyramidal cells might be related to the critical period of early postnatal development.

Aging↗
PubMed1999

Calbindin immunoreactivity in the developing and adult human cerebellum.

Calbindin (CALB), a calcium-binding protein, is known to be expressed in the embryonic nervous system. In this study, we have examined its distribution in the cerebellum of human fetuses (11-25 weeks of gestation) and adult by immunohistochemistry. At the gestational age of 11-12 weeks. CALB immunoreactivity was present in granule and Purkinje cells throughout the cerebellum. By 16-21 weeks of gestation, immunoreactive Purkinje cells were well-differentiated in the vermis and flocculus, and their axons ran towards the deep cerebellar nuclei area, while the axon collaterals were seen to be distributed into adjacent folia. At the gestational period of 24-25 weeks, most Purkinje cells of the flocculus and vermis were arranged in one to two rows, while those of the hemispheres were still undifferentiated. A few Golgi cells of the vermis showed immunoreactivity. The neurons of the deep nuclei were immunonegative right from the gestational age of 11 weeks although a fine stippled staining of fibers was present throughout the body of all nuclei. The fibers lying close to the hilum of the dentate nucleus were strongly CALB-positive. The vestibulocerebellar fibers, being traced at the level of lower pons and upper medulla oblongata were stained as early as 11 weeks of gestation, whereas the olivocerebellar fibers were stained from 16 weeks onward. In the adult cerebellum, Purkinje cells were moderately immunopositive while granule cells were faintly stained; no other cells, including those of the deep nuclei were stained. In the medulla oblongata, the inferior olivary nucleus and olivocerebellar fibers were strongly CALB-positive. Our results indicate that CALB is expressed in early migratory Purkinje cells, and their maturation occurs in a vermal-to-hemisphere gradient. It is likely that CALB plays a significant role in the regulation of Ca2+-dependent activities in the developing cerebellum.

Adult↗
PubMed1992

Visual deprivation fails to reduce calbindin 28kD or GABA immunoreactivity in the rhesus monkey superior colliculus.

Antibody labeling of the calcium-binding protein calbindin 28kD (CaBP) and gamma-aminobutyric acid (GABA) is altered by short-term monocular deprivation in the lateral geniculate nucleus and visual cortex of adult primates. It is not known whether these alterations occur in other subcortical visual structures. We therefore have examined antibody labeling to CaBP and GABA in the superior colliculus (SC) of visually deprived Rhesus monkeys. One group was monocularly enucleated as adults. The other monkeys experienced different types of monocular and binocular deprivation from birth, including occlusion of one eye, and/or surgically induced aphakia, optically corrected with extended-wear contact lenses, or an intraocular lens implant. Some of these monkeys also had one eye enucleated prior to perfusion. In the SC of normal monkeys, CaBP-immunoreactive neurons formed three laminar tiers within SC, one within the zonal layer (ZL) and upper superficial gray layer (SGL), another bridging the optic and intermediate gray layers, and a third within the deep gray layer. CaBP neurons within the upper tier had small pyriform or stellate morphologies while those in the deeper tiers were slightly larger neurons, most with a stellate morphology. GABA-immunoreactive neurons were densely distributed within the SGL and more sparsely distributed within the deeper layers. These cells were mostly small neurons with horizontal, pyriform, or stellate morphologies. Neither monocular enucleation nor occlusion nor aphakia combined with continuous occlusion of the fellow eye produced any visible reduction in antibody labeling in cells or neuropil within the SC. Full-field measures of labeling intensity (optical density) within the ZL and upper SGL revealed no consistent differences between the SC contralateral or ipsilateral to the affected eye in either CaBP- or GABA-labeled sections. Measures of the optical density, number, and size of labeled neurons also showed no consistent effects of enucleation and/or occlusion. We therefore conclude that the retino-geniculostriate and retino-collicular systems differ in their response to deprivation which is likely due to the significant overlap of retinal axons from the two eyes that occurs in the SC of the Rhesus monkey.

Animals↗
PubMedDate not supplied

Discrete reduction patterns of parvalbumin and calbindin D-28k immunoreactivity in the dorsal lateral geniculate nucleus and the striate cortex of adult macaque monkeys after monocular enucleation.

We analyzed the immunohistochemical distribution of the two calcium-binding proteins, parvalbumin (PV) and calbindin D-28k (CB), in the primary visual cortex and lateral dorsal geniculate nucleus (dLGN) of monocularly enucleated macaque monkeys (Macaca fascicularis and Macaca nemestrina) in order to determine how the expression of PV and CB is affected by functional inactivity. The monkeys survived 1-17 weeks after monocular enucleation. The distribution pattern of each of the proteins was examined immunocytochemically using monoclonal antibodies and compared with that of the metabolic marker cytochrome oxidase (CO). We recorded manually the number of immunostained neurons and estimated the concentration of immunoreactive staining product using a computerized image-acquisition system. Our results indicate a decrease of approximately 30% in the labeling of PV-immunoreactive (ir) neuropil particularly in those layers of denervated ocular-dominance columns receiving the geniculocortical input. There was no change in the number of PV-ir neurons in any compartment irrespective of the enucleation interval. For CB-ir, we found a 20% decrease in the neuropil labeling in layer 2/3 of the denervated ocular-dominance columns. In addition, a subset of pyramidal CB-ir neurons in layers 2 and 4B, which are weakly stained in control animals, showed decreased labeling. In the dLGN of enucleated animals, PV-ir and CB-ir were decreased only in the neuropil of the denervated layers. From these results, we conclude that cortical interneurons and geniculate projection neurons still express PV and CB in their cell bodies after disruption of the direct functional input from one eye. The only distinct decrease of PV and CB expression is seen in axon terminals from retinal ganglion cells in the dLGN, and in the axons and terminals of both geniculocortical projection cells and cortical interneurons in the cerebral cortex.

Animals↗
PubMed1992

Monocular enucleation reduces immunoreactivity to the calcium-binding protein calbindin 28 kD in the rhesus monkey lateral geniculate nucleus.

The calcium-binding proteins calbindin (CaBP) and parvalbumin (PV) are important in regulating intracellular calcium in brain cells. PV immunoreactivity is reduced by enucleation in the lateral geniculate nucleus (LGN) and by enucleation and visual deprivation in the striate cortex of adult monkeys. The effects of enucleation and visual deprivation on CaBP immunoreactivity in the LGN are not known. We therefore have studied cells and neuropil in the LGN that are labeled by antibodies to CaBP in normal and visually deprived Rhesus monkeys to determine if there is an effect on this calcium-binding protein. One group of monkeys had one eye removed 2 weeks to 4.3 years before sacrifice. A second group had one eye occluded with opaque lenses from infancy without enucleation. A final group had one eye occluded long-term followed by short-term enucleation 2 weeks before sacrifice. In normal monkeys, CaBP-immunoreactive neurons were found throughout the LGN. They were sparsely distributed within the six main laminae, and more densely distributed within layer S and the interlaminar zones (ILZ). The labeled ILZ neurons had a distinct morphology, with fusiform somata and elaborate dendritic trees that were confined primarily to the ILZ. Most CaBP-labeled neurons in the main layers had dendrites that radiated in all directions from the soma. ILZ and main layer cells labeled by CaBP thus probably represent two different cell types. Monocular enucleation with or without occlusion produced a significant reduction in antibody labeling in the deafferented laminae. Field measures revealed an average 11.5% reduction in optical density in each deafferented lamina compared to its adjacent, nondeprived layer. The differences in field optical density between deprived and nondeprived layers were statistically significant. CaBP neurons were still visible, but the optical density of antibody labeling in these cells also was reduced. Occlusion without enucleation had no effect. Thus, deafferentation, but not light deprivation, reduces concentrations of CaBP in monkey LGN. This effect is different than that seen in striate cortex of adult monkeys, where visual deprivation as well as enucleation alters CaBP immunoreactivity.

Animals↗
PubMed1991

Ion-binding properties of calbindin D9k: a Monte Carlo simulation study.

Monte Carlo simulations are used to calculate the binding constant of two Ca2+ ions to the protein bovine calbindin D9k. The change in binding constant with respect to mutation of charged amino acids, presence of various electrolytes, protein concentration, solution pH, and competitive binding of monovalent ions is investigated. Each of these factors may have a large influence on the binding constant. The simulations are performed in a dielectric continuum model, the so-called primitive model of electrolyte theory, with a fixed protein structure and a uniform dielectric permittivity. The calculated binding constants are in excellent agreement with experimental data and describe changes in the binding constant over six orders of magnitude.

Animals↗
PubMed1987

Structure-function relationships in EF-hand Ca2+-binding proteins. Protein engineering and biophysical studies of calbindin D9k.

Genes encoding the minor A component of bovine calbindins D9k--the smallest protein known with a pair of EF-hand calcium-binding sites--with amino acid substitutions and/or deletions have been synthesized and expressed in Escherichia coli and characterized with different biophysical techniques. The mutations are confined to the N-terminal Ca2+-binding site and constitute Pro-20----Gly (M1), Pro-20----Gly and Asn-21 deleted (M2), Pro-20 deleted (M3), and Tyr-13----Phe (M4). 1H, 43Ca, and 113Cd NMR studies show that the structural changes induced are primarily localized in the modified region, with hardly any effects on the C-terminal Ca2+-binding site. The Ca2+ exchange rate for the N-terminal site changes from 3 s-1 in the wild-type protein (M0) and M4 to 5000 s-1 in M2 and M3, whereas there is no detectable variation in the Ca2+ exchange from the C-terminal site. The macroscopic Ca2+-binding constants have been obtained from equilibration in the presence of the fluorescent chelator 2-[[2-[bis(carboxymethyl)-amino]- 5-methylphenoxy]methyl]-6-methoxy-8-[bis(carboxymethyl)amino]quinoline or by using a Ca2+-selective electrode. The Ca2+ affinity of M4 was similar to that of M0, whereas the largest differences were found for the second stoichiometric step in M2 and M3. Microcalorimetric data show that the enthalpy of Ca2+ binding is negative (-8 to -13 kJ.mol-1) for all sites except the N-terminal site in M2 and M3 (+5 kJ.mol-1). The binding entropy is strongly positive in all cases. Cooperative Ca2+ binding in M0 and M4 was established through the values of the macroscopic Ca2+-binding constants. Through the observed changes in the 1H NMR spectra during Ca2+ titrations we could obtain ratios between site binding constants in M0 and M4. These ratios in combination with the macroscopic binding constants yielded the interaction free energy between the sites delta delta G as -5.1 +/- 0.4 kJ.mol-1 (M0) and less than -3.9 kJ.mol-1 (M4). There is evidence (from 113Cd NMR) for site-site interactions also in M1, M2, and M3, but the magnitude of delta delta G could not be determined because of sequential Ca2+ binding.

Aminoquinolines↗
PubMed1990

Protein surface charges and Ca2+ binding to individual sites in calbindin D9k: stopped-flow studies.

The kinetics of calcium dissociation from two groups of site-specific mutants of calbindin D9k--a protein in the calmodulin superfamily with two Ca2+ sites and a tertiary structure closely similar to that of the globular domains of troponin C and calmodulin--have been studied by stopped-flow kinetic methods, using the fluorescent calcium chelator Quin 2, and by 43Ca NMR methods. The first group of mutants comprises all possible single, double, and triple neutralizations of three particular carboxylate groups (Glu-17, Asp-19, and Glu-26) that are located on the surface of the protein. These carboxylates are close to the two EF-hand calcium binding sites, but are not directly liganded to the Ca2+ ions. Conservative modification of these negative carboxylate side chains by conversion to the corresponding amides results in a marked reduction in the Ca2+ binding constants for both sites, as recently reported [Linse et al. (1988) Nature 335, 651-652]. The stopped-flow kinetic results show that this reduction in Ca2+ affinity derives primarily from a reduction in the Ca2+ association rate constant, kon. The estimated maximum value of the association rate constant (kon(max) for Ca2+ binding to the wild-type protein is ca. 10(9) M-1 s-1. In contrast, for the mutant protein with three charges neutralized the maximum association rate constant is estimated to be only 2 X 10(7) M-1 s-1.(ABSTRACT TRUNCATED AT 250 WORDS)

Binding Sites↗
PubMed1990

The rate and structural consequences of proline cis-trans isomerization in calbindin D9k: NMR studies of the minor (cis-Pro43) isoform and the Pro43Gly mutant.

The EF-hand calcium-binding protein, calbindin D9k, exists in solution in the calcium-loaded state, as a 1:3 equilibrium mixture of two isoforms, the result of cis-trans isomerism at the Gly42-Pro43 peptide bond [Chazin et al. (1989) Proc. Natl. Acad. Sci. U.S.A. 86, 2195-2198]. Nuclear magnetic resonance (NMR) studies of the minor (cis-Pro43) isoform and the Pro43----Gly mutant are reported here. The rate of cis----trans isomerization at the Pro43 peptide bond in the wild-type protein was determined by line-shape analysis at elevated temperatures, using a sample in which all amino acids, except Ser and Val, were deuterated. The cis----trans rate is calculated to be 0.2 s-1 at 25 degrees C, corresponding to a free energy of activation, delta G, of 77 kJ/mol. The complete sequence-specific 1H NMR assignments of the cis-Pro43 isoform and the Pro43----Gly mutant in the calcium-loaded state have been obtained by using standard methods combined with comparisons to the previously assigned major (trans-Pro43) isoform. This has permitted detailed comparative analysis of 1H NMR chemical shifts, backbone scalar coupling constants, and nuclear Overhauser effects. The minor isoform has a global fold that is identical with that of the major isoform. Structural changes imposed by cis-trans isomerization at Pro43 are highly localized to the linker loop (containing Pro43) that joins the two EF hands. The Pro43----Gly mutant has a global fold that is identical with the wild-type protein, but does not exhibit conformational heterogeneity. Only very limited structural differences are observed between mutant and wild-type protein, and these are also highly localized to the linker loop. The ion-binding properties of the mutant, as determined by 43Ca and 113Cd NMR, are found to be very similar to the wild-type protein. These results provide crucial evidence that justifies the calculation of high-resolution three-dimensional structures of the Pro43Gly mutant, rather than of the conformationally heterogeneous wild-type protein.

Amino Acid Sequence↗
PubMed1990

1H NMR resonance assignments, secondary structure, and global fold of Apo bovine calbindin D9k.

The solution structure and dynamics of apo bovine calbindin D9k have been studied by a wide range of two-dimensional 1H nuclear magnetic resonance experiments. Due to the presence of conformational heterogeneity in the wild-type protein, the sequential resonance assignment was carried out on a Pro43----Gly mutant. By use of a combination of scalar correlation experiments acquired from H2O solution, 61 of the 76 1H spin systems could be assigned to particular amino acid types. The remaining resonances were assigned by a parallel series of experiments acquired from 2H2O solution. These spin system assignments provided a basis for complete sequential resonance assignments from interresidue backbone nuclear Overhauser effects (NOEs). Elements of secondary structure were identified from sequential and medium-range NOEs, backbone spin-spin coupling constants, and slowly exchanging amide protons. Four sections of helix are delineated, together with a short antiparallel beta-sheet interaction between the peptide loops involved in Ca2+ binding. The global fold is provided by combining these elements of secondary structure with a subset of the long-range, interhelix NOEs. Comparison with similar studies on the Ca2(+)-saturated protein indicates that at this crude level the structures are very similar. However, removal of the Ca2+ does dramatically affect the dynamics of the protein, as judged by amide proton exchange rates and aromatic ring rotation. This is particularly evident in the increased flexibility of the residues in the hydrophobic core.

Amides↗
PubMed2001

Calbindin D(9k): a protein optimized for calcium binding at neutral pH.

The binding of calcium ions by EF-hand proteins depends strongly on the electrostatic interactions between Ca(2+) ions and negatively charged residues of these proteins. We have investigated the pH dependence of the binding of Ca(2+) ions by calbindin D(9k). This protein offers a unique possibility for interpretation of such data since the pK(a) values of all ionizable groups are known. The binding is independent of pH between 7 and 9, where maximum calcium affinity is observed. An abrupt decrease in the binding affinity is observed at pH values below 7. This decrease is due to protonation of acidic groups, leading to modification of protein charges. The pH dependence of the product of the two macroscopic Ca(2+)-binding constants can be formally described by the involvement of two acidic groups with pK(a) = 6.6. Monte Carlo calculations show that the reduction of Ca(2+) binding is strictly determined by variable electrostatic interactions due to pH-dependent changes not only in the binding sites, but also of the overall charge of the protein.

Calbindins↗
PubMed2002

A 15N NMR mobility study on the dicalcium P43M calbindin D9k and its mono-La3+-substituted form.

Calbindin D(9k) is a dicalcium binding protein consisting of two helix-loop-helix EF-hand motifs joined together by a flexible linker region where one metal ion can bind to each of the two loops. A proline residue at position 43 in the linker region displays cis-trans isomerism in the wild-type (WT) protein. Such isomerism appeared to be removed by substituting the proline with a glycine or a methionine in the P43G or P43M mutant. We have extended the available mobility studies on the P43M mutant through amide (15)N R(1), R(2), and R(1)(rho)() measurements. This has revealed unexpected conformational equilibria on the millisecond time scale involving residues 38, 42-44, and 46 in the linker region and residues 18 and 19 in calcium binding site I with similar energy barriers. These data are discussed in comparison with those available for the WT, as well as the apo-, mono-, and disubstituted P43G mutant. Quantification of water-amide proton exchange rates using saturation transfer and qualitative application of (15)N-(CLEANEX-PM)-FHSQC shows the values are in agreement with high mobility for the above-mentioned residues. Cross correlation between N-H dipole-dipole relaxation and (15)N CSA relaxation indicates that some of these mobility differences may extend to the sub-nanosecond time scale. Similar data were also obtained for the derivative where the calcium ion in the C-terminal loop was replaced with lanthanum. The results presented here show that, contrary to expectations, there are significant differences in dynamics between the dicalcium state of P43G and P43M and that these differences are not confined to the flexible linker region containing the point mutation. They also demonstrate that substitution of a lanthanide ion for calcium, which is a common procedure, does not significantly alter the mobility of the native protein.

Amides↗
PubMed2006

Conformational study of silk-like peptides containing the calcium-binding sequence from calbindin D9k using 13C CP/MAS NMR spectroscopy.

The calcium-binding sites of calbindin D(9k) have a helix-loop-helix motif. In this study, the helix motifs were replaced by several Ala-Gly repeating regions designed on the basis of the primary sequences of several silk fibroins. The synthesized peptides were treated with several organic solvents to modify the secondary structure of the Ala-Gly repeating regions. The local structures of the Ala-Gly repeating regions, as well as the calcium-binding motif, D(9k)-loop (D(9k)L), were determined by (13)C CP/MAS NMR spectroscopy. In the four peptides containing D(9k)L synthesized, the poly(Ala) domains retain the ability to undergo a conformational transition from alpha-helical to beta-sheet in (A)(12)-D(9k)L despite the presence of the D(9k)L domain at the center of the peptide molecule, but the presence of this domain in the other model peptides synthesized has a marked effect on the conformation of the added silk-like domains. The results showed that the structures of the Ala-Gly repeating regions can be controlled by the choice of both the organic solvent and the amino acid sequence of the Ala-Gly repeating regions without disrupting the secondary structure of D(9k)L suggesting that it may retain its ability to bind calcium ions.

Binding Sites↗
PubMed2005

(4,2)D Projection--reconstruction experiments for protein backbone assignment: application to human carbonic anhydrase II and calbindin D(28K).

Projection-reconstruction NMR experiments have been shown to significantly reduce the acquisition time required to obtain protein backbone assignment data. To date, this concept has only been applied to smaller (15)N/(13)C-labeled proteins. Here, we show that projection-reconstruction NMR techniques can be extended to larger protonated and perdeuterated proteins. We present a suite of (4,2)D triple-resonance experiments for protein backbone assignment and a Hybrid Backprojection/Lower-Value algorithm for reconstructing data with relatively weak signal-to-noise ratios. In addition, we propose a sampling theorem and discuss its implication on the choice of projection angles. We demonstrate the efficacy of this approach using the 29 kDa protein, human carbonic anhydrase II and the 30 kDa protein, calbindin D(28K).

Calbindins↗
PubMed2001

Paramagnetism-based versus classical constraints: an analysis of the solution structure of Ca Ln calbindin D9k.

The relative importance of paramagnetism-based constraints (i.e. pseudocontact shifts, residual dipolar couplings and nuclear relaxation enhancements) with respect to classical constraints in solution structure determinations of paramagnetic metalloproteins has been addressed. The protein selected for the study is a calcium binding protein, calbindin D9k, in which one of the two calcium ions is substituted with cerium(III). From 1823 NOEs, 191 dihedral angles, 15 hydrogen bonds, 769 pseudocontact shifts, 64 orientational constraints, 26 longitudinal relaxation rates, plus 969 pseudocontact shifts from other lanthanides, a final family with backbone r.m.s.d. from the average of 0.25 A was obtained. Then, several families of structures were generated either by removing subsets of paramagnetism-based constraints or by removing increasing numbers of NOEs. The results show the relative importance of the various paramagnetism-based constraints and their good complementarity with the diamagnetic ones. Although a resolved structure cannot be obtained with paramagnetism-based constraints only, it is shown that a reasonably well resolved backbone fold can be safely obtained by retaining as few as 29 randomly chosen long-range NOEs using the standard version of the program PSEUDYANA.

Amino Acid Substitution↗
PubMed2002

Cross correlation rates between Curie spin and dipole-dipole relaxation in paramagnetic proteins: the case of cerium substituted calbindin D9k.

Cross correlation rates between Curie spin relaxation and H-N dipole-dipole coupling (gamma(HM,HN)CS,DD) have been determined for a calcium binding protein, Calbindin D9k, in which one of the two calcium ions is substituted with cerium(III). Gamma(HM,HN)CS,DD values depend on both the metal-to-proton distances and the M-H-N angles and can be used as an additional constraint in order to refine the solution structure of paramagnetic metalloproteins. For this purpose, we have implemented a new module (CCR-DYANA) in a version of the program DYANA (PARAMAGNETIC-DYANA), which can be used together with other paramagnetism-based constraints such as pseudocontact shifts, residual dipolar couplings and hyperfine based Karplus relationships. This integrated structure calculation protocol has the advantage that different paramagnetic-based constraints are treated by the same algorithm in a way that the efficiency of each class of constraints can be analyzed and compared.

Algorithms↗
PubMed1997

Protein solution structure calculations in solution: solvated molecular dynamics refinement of calbindin D9k.

The three-dimensional solution structures of proteins determined with NMR-derived constraints are almost always calculated in vacuo. The solution structure of (Ca2+)2-calbindin D9k has been redetermined by new restrained molecular dynamics (MD) calculations that include Ca2+ ions and explicit solvent molecules. Four parallel sets of MD refinements were run to provide accurate comparisons of structures produced in vacuo, in vacuo with Ca2+ ions, and with two different protocols in a solvent bath with Ca2+ ions. The structural ensembles were analyzed in terms of structural definition, molecular energies, packing density, solvent-accessible surface, hydrogen bonds, and the coordination of calcium ions in the two binding loops. Refinement including Ca2+ ions and explicit solvent results in significant improvements in the precision and accuracy of the structure, particularly in the binding loops. These results are consistent with results previously obtained in free MD simulations of proteins in solution and show that the rMD refined NMR-derived solution structures of proteins, especially metalloproteins, can be significantly improved by these strategies.

Calbindins↗
PubMed2000

Dietary short-chain fructooligosaccharides increase calbindin-D9k levels only in the large intestine in rats independent of dietary calcium deficiency or serum 1,25 dihydroxy vitamin D levels.

Dietary short-chain fructooligosaccharides (Sc-FOS) increase mucosal calbindin-D9k (CaBP) levels in the large intestine whereas levels in the small intestine are decreased in rats. In the present study, we investigated the mechanism by which Sc-FOS induce this increase in CaBP in the large intestine by measuring intestinal CaBP levels in rats fed normal and calcium-deficient diets. Dietary groups included a calcium-containing (0.5%) diet with or without Sc-FOS (100 g/kg diet) and a calcium-deficient (abt. 0.01%) diet with or without Sc-FOS (100 g/kg diet). The rats were fed these diets for 10 days following which they were killed and the intestine removed for collection of the entire mucosa which was divided into four segments, i.e., proximal and distal segments of the small intestine, the cecum and the colorectum. Mucosal CaBP and plasma calcium (Ca), 1,25-dihydroxycholecalciferol (1,25(OH)2D3), 25-hydroxycholecalciferol (25(OH)D3), parathyroid hormone (PTH) and calcitonin levels were measured. Feeding of calcium deficient diet resulted in an increase in CaBP levels in the small intestine, but did not influence levels in the large intestine. Moreover, a significant positive correlation between plasma 1,25(OH)2D3 and CaBP levels in the case of both small intestinal segments (proximal, r = 0.77012, p < 0.00007; distal, r = 0.75056, p < 0.00014) was observed, but not in the case of the large intestinal segments. Sc-FOS increased CaBP levels in the large intestine. These results suggest that the large intestinal CaBP levels do not change in response to dietary calcium conditions and are not regulated by circulating 1,25(OH)2D3 indicating that the effect of Sc-FOS on CaBP levels in the large intestine is independent of the action of 1,25(OH)2D3.

Animals↗