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At least 1,135 records · Page 63Linked to original sources
PubMed1986

1,25-Dihydroxyvitamin D3-mediated intestinal calcium transport. Biochemical identification of lysosomes containing calcium and calcium-binding protein (calbindin-D28K).

A variety of intestinal cell organelles and proteins have been proposed to mediate 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3)-stimulated calcium absorption. In the present study biochemical analyses were undertaken to determine the subcellular localization of 45Ca after calcium transport in vivo in ligated duodenal loops of vitamin D-deficient chicks injected with 1.3 nmol of 1,25-(OH)2D3 or vehicle 15 h prior to experimentation. Separation of Golgi, mitochondria, basal lateral membrane, and lysosome fractions in the epithelial homogenates was achieved by differential sedimentation followed by centrifugation in Percoll gradients and evaluation of appropriate marker enzyme activities. Both vitamin D-deficient and 1,25-(OH)2D3-treated chicks had the highest levels of 45Ca-specific activity in lysosomal fractions. The lysosomes were also the only organelles to exhibit a 1,25-(OH)2D3-mediated difference in calcium content, increasing to 138% of controls. Lysosomes prepared from 1,25-(OH)2D3-treated chicks also contained the greatest levels of immunoreactive calbindin-D28k (calcium-binding protein). Chloroquine, a drug known to interfere with lysosomal function, was tested and found to inhibit 1,25-(OH)2D3-stimulated intestinal calcium absorption. Neither 1,25-(OH)2D3 nor chloroquine affected [3H]2O transport. In additional experiments, microsomal membranes (105,000 X g pellets) were subjected to gradient centrifugation. The highest levels of 45Ca-specific activity and calcium-binding protein in material from 1,25-(OH)2D3-treated chicks were found in fractions denser than endoplasmic reticulum and may represent endocytic vesicles. In studies on intestinal mucosa of 1,25-(OH)2D3-treated birds fractionated after 30 min of exposure to lumenal Ca2+ or Ca2+ plus chloroquine, 45Ca was found to accumulate in lysosomes and putative endocytic vesicles, relative to controls. A mechanism involving vesicular flow is proposed for 1,25-(OH)2D3-mediated intestinal calcium transport. Endocytic internalization of Ca2+, fusion of the vesicles with lysosomes, and exocytosis at the basal lateral membrane complete the transport process.

Acid Phosphatase↗
PubMed1986

Effects of alpha-amanitin and cycloheximide on 1,25-dihydroxyvitamin D3-dependent calbindin-D28K and its mRNA in vitamin D3-replete chick intestine.

We have examined the effects of the transcriptional inhibitor alpha-amanitin and the translational inhibitor cycloheximide on levels of calbindin-D28K (28-kDa calcium binding protein, CaBP) and CaBP-mRNA in the vitamin D-replete chick intestine. Chicks were raised on one of four diets: "normal" (1% calcium, 0.6% phosphorus); high calcium (3.3% calcium, 0.5% phosphorus); low calcium (0.3% calcium, 0.6% phosphorus); or low phosphorus (1% calcium, 0.09% phosphorus). Chicks were then treated either with alpha-amanitin (20 micrograms/chick) or cycloheximide (600 micrograms/chick) 2 h prior to a dose of 6.5 nmol of 1,25-dihydroxyvitamin D3. Duodenal mucosa was collected from 0 to 120 min afterward and assayed for CaBP-mRNA by dot blot hybridization and for CaBP using an enzyme-linked immunosorbent assay. In the absence of inhibitor, CaBP levels were depressed by high calcium and elevated by low calcium or low phosphorus, as expected. These changes occurred, however, without a change in CaBP-mRNA levels. alpha-Amanitin had no effect on CaBP or on CaBP-mRNA levels in chicks raised on any of the diets. Cycloheximide inhibited CaBP levels, and surprisingly also inhibited CaBP-mRNA levels in all four dietary groups. These results indicate that continual protein synthesis is necessary for the expression of CaBP-mRNA, suggesting the existence of a rapidly turned over protein that may be required for stabilization or for processing of the chick intestinal CaBP messenger RNA.

Amanitins↗
PubMed1995

Calbindin D28k in the olivocerebellar projection. A light and electron microscope study.

The distribution of the calcium binding protein calbindin D28k (CaBP) in the rat and gerbil olivocerebellar system was compared and an ultrastructural analysis of the inferior olive and cerebellum was performed in the gerbil. CaBP is present in the perikarya and dendritic arborisations of inferior olivary neurons. The olivocerebellar projection in the inferior cerebellar peduncle stains for CaBP. CaBP is also contained in the terminal branches of the olivocerebellar projection: the climbing fibres in the inner molecular layer of the cerebellum. Thus CaBP is a reliable marker for the whole olivocerebellar projection in adult rodents. Presence of the calcium binding protein CaBP in inferior olivary neurons may influence the different calcium conductances of their dendritic, somatic and terminal compartments responsible for the physiological properties of these nerve cells.

Animals↗
PubMed1992

Absence of calbindin-D28 expression in nonclassical 1,25-dihydroxyvitamin D targets: analysis by polymerase chain reaction.

CaBP-D28 mRNA expression in rat heart, testis, and lung was assessed by polymerase chain reaction (PCR). The animal model used was the hyperinduced vitamin D-treated rat (100 ng 1,25-dihydroxyvitamin D subcutaneously, daily for 7 days). For the PCR studies, two pairs of 20 mer oligonucleotide primers (designated 1-4 according to their position on the coding strand, but with primers 3 and 4 in reverse orientation) derived from the rat CaBP-D28 cDNA sequence were tested in various combinations. Optimal conditions were established using a 1:100 dilution of cDNA from normal rat kidney. Bands of the predicted sizes of 869 (1, 3), 994 (1, 4), 725 (2, 3), and 850 (2, 4) nucleotide base pairs resulted, but with varying intensities: 2,4 approximately 1,3 > 1,4 > 2,3. Repeat PCR (recycling after 1:100 dilution and readdition of reagents and primers with at least one different primer) provided strong additional amplification, particularly with the 1,4/2,4 combination. Under these conditions, mixing experiments showed that CaBP-D28 transcripts were detectable at 10(-7)- to 10(-9)-fold lower levels of expression than in D+ kidney. When RNA was isolated and cDNA generated from test tissues from 4 individual vitamin D-stimulated (D+) and vitamin D-deficient (D-) rats, repeat PCR (1,4/2,4 primer combination) provided no evidence of significant CaBP-D28 mRNA expression in the nonclassic target tissues, in contrast to strong bands in both the D- kidney (undiluted) and D+ kidney (1:100 dilution) preparations.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗