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J J Feher

Publications and source records attributed to J J Feher.

45 records · Page 3Linked to original sources
PubMed1983

Facilitated calcium diffusion by intestinal calcium-binding protein.

The calcium flux through an aqueous compartment was determined using a flow-through dialysis cell in which two dialysis membranes isolated the aqueous compartment. Addition of the intestinal vitamin D-dependent calcium-binding protein (CaBP) significantly enhanced the calcium flux at near physiological calcium concentrations (1 X 10(-6) M). Bovine serum albumin had no effect on the calcium flux. CaBP appears to be one of a class of low molecular weight, soluble binding proteins that enhance ligand diffusion.

Animals↗
PubMed1982

The effect of calcium load on the calcium permeability of sarcoplasmic reticulum.

The effect of intravesicular and extravesicular calcium concentration on the passive efflux from sarcoplasmic reticulum (SR) vesicles isolated from cardiac and skeletal muscle was determined by measuring net efflux of calcium after stopping pump-mediated fluxes. The apparent permeability, calculated as the passive efflux divided by the total intravesicular calcium, depended on calcium load. This dependence of the apparent permeability on calcium load could be explained by the presence of intravesicular calcium-binding sites with a dissociation constant less than 10(-3) M. When the intravesicular bound calcium was taken into account, passive calcium efflux was found to be linearly related to the difference in calcium concentration across the SR membrane. Thus the permeability of the SR membrane is independent of intravesicular and extravesicular calcium concentration in the ranges investigated. The average first order rate constant for passive calcium efflux for six preparations was 0.8 +/- 0.2 min-1 for skeletal and 0.7 +/- 0.1 min-1 for cardiac SR. The amount of intravesicular bound calcium for the same preparations was 33 +/- 6 nmol mg-1 for skeletal and 13 +/- 2 nmol mg-1 for cardiac SR. The first order rate constants were unaffected by Mg concentration between 0.1 +/- 15.1 mM and by the presence of an ATP-regenerating system. The results suggest that some minimal calcium load may be required in order to observe a substantial passive calcium efflux, the passive calcium efflux is not carrier mediated, and passive calcium efflux is not a likely route of calcium release during excitation-contraction coupling.

Animals↗
PubMed1979

Studies on the subcellular localization of the membrane-bound fraction of intestinal calcium-binding protein.

Sorbitol density gradient centrifugation applied to intestinal mucosa homogenates resulted in a complete separation of soluble calcium-binding protein from the bound fraction of calcium-binding protein, providing further documentation of the bound pool of calcium-binding protein. The peak of the bound calcium-binding protein was not associated with the major peaks of any of the markers used, but was associated with minor peaks of alkaline phosphatase, RNA, and glucose-6-phosphatase. Lack of association of bound calcium-binding protein with (Na+ + K+)-ATPase indicated that the bound calcium-binding protein is not on the basolateral membrane. Differential centrifugation fractionation indicated that the bound calcium-binding protein is not associated with nuclei or mitochondria. The bound calcium-binding protein also could not be detected in partially purified brush borders. Exclusion of the brush border and basolateral membranes as the location of the bound calcium-binding protein suggests an intracellular locale.

Alkaline Phosphatase↗
PubMed1979

Calcium absorption and intestinal calcium-binding protein: quantitative relationship.

The concentration of the vitamin D-induced calcium-binding protein (CaBP) and calcium absorption from the duodenum were investigated in chicks with an in vivo ligated-loop technique. The relation between CaBP and calcium absorption was dependent on a) source of vitamin D activity (either vitamin D3 or 1,25-dihydroxycholecalciferol); b) dosage of vitamin D3; c) time after administration of vitamin D3 to rachitic animals. To aid in the interpretation of these results, a phenomenological model was developed in which CaBP was viewed as being linearly related to a portion of calcium absorption. The model, when applied to the data, suggests that there is a "nonfunctional" pool of CaBP the size of which is determined by the vitamin D status of the animal. After correction for this nonfunctional pool, the proportionality between CaBP and calcium absorption is independent of the vitamin D status of the animal.

Animals↗
PubMed1979

Intestinal calcium-binding protein and calcium absorption in cortisol-treated chicks: effects of vitamin D3 and 1,25-dihydroxyvitamin D3.

Vitamin D3 in rachitic chicks stimulates calcium absorption and induces the synthesis of two pools of intestinal calcium-binding protein (CaBP), one soluble and the other membrane bound. Cortisol acetate caused a decrease in calcium absorption which was accompanied by a decrease in soluble CaBP. Cortisol was similarly effective in 1,25-dihydroxyvitamin D3-dosed chicks, suggesting that the glucocorticoid effect was not entirely due to the defective synthesis of this metabolite. Ca absorption was directly correlated with soluble CaBP and alkaline phosphatase and inversely related to the ratio of bound to soluble CaBP. It was further observed that the slope of the Ca absorption vs. soluble CaBP regression line was greater in chicks given 1,25-dihyroxyvitamin D3 compared to those given vitamin D3, and this is interpreted to mean that another factor or condition, in addition to assayed concentrations of soluble CaBP, determines the degree of calcium absorption.

Alkaline Phosphatase↗
PubMed1978

Evidence for a membrane-bound fraction of chick intestinal calcium-binding protein.

After homogenization of intestinal mucosa from vitamin D-replete chicks and high speed centrifugation, the major proportion of the vitamin D-induced calcium-binding protein is present in the supernatant fraction. However, the centrifugate, after repeated washing, contains significant amounts of bound calcium-binding protein that can be solubilized by Triton X-100. The bound calcium-binding protein is identical to soluble calcium-binding protein by the criteria of immunological identity, electrophoretic mobility, and molecular size, as determined by gel filtration chromatography. The bound calcium-binding protein is only partially released by sonication, osmotic shock or by ribonuclease treatment. Bound and soluble calcium-binding protein are not present in rachitic chick intestine. The addition of calcium-binding protein to rachitic mucosa prior to homogenization does not yield a Triton X-100 solubilizable form, indicating that bound calcium-binding protein in vitamin D-replete intestine is not due to adsorption or vesicular entrapment of soluble calcium-binding protein. The overall evidence suggests that part of the intestinal calcium-binding protein is membrane-bound.

Animals↗
PubMedDate not supplied

Comparison of the enhanced steady-state diffusion of calcium by calbindin-D9K and calmodulin: possible importance in intestinal calcium absorption.

The diffusion of calcium was measured using the unidirectional flux of 45Ca across an aqueous layer. The aqueous layer was bounded by two dialysis membranes and convection was eliminated by gelling the aqueous layer with agarose. The apparent self-diffusion coefficient was determined by the dependence of the tracer flux on the diffusion distance. The apparent self-diffusion coefficient increased linearly with the concentration of calbindin-D9K and calmodulin, but the effect of calmodulin was markedly less than that of calbindin-D9K. This difference is attributed to the lower association constant for calmodulin. The ion-exchange resin Chelex-100 also increased the steady-state of 45Ca, but the effect of Chelex-100 was much less efficient than the effect of calbindin-D9K. The mechanism of enhanced diffusion was attributed to an enhanced gradient of total 45Ca. These results indicate that the steady-state unidirectional calcium flux is a superposition of free calcium diffusion and bound calcium diffusion, with only a small contribution due to a 'bucket brigade' mechanism. We suggest that this phenomenon may be important in calcium absorption across the intestine.

Animals↗