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Biomedical subjects

E Gylfe

Publications and source records attributed to E Gylfe.

At least 109 records · Page 6Linked to original sources
PubMed1988

Calcium-agonistic action of Mn2+ in the parathyroid cell.

The effects of 3.0 mM Mn2+ on parathyroid hormone (PTH) release, 45Ca fluxes and the cytoplasmic Ca2+ concentration (Ca2+i) were studied in vitro with use of parathyroid glands from rats and cattle. Mn2+ inhibited PTH release by about 70 and 60% at Ca2+ concentrations of less than 10 nM or 0.5 mM, respectively, and like the inhibitory effect of Ca2+, that of Mn2+ was rapid and reversible. Mn2+-induced inhibition of the PTH release was associated with reduction of 45Ca uptake by about 50% and a marked but temporary increase in 45Ca efflux. Mn2+ induced a rapid transient increase in Ca2+i provided that the intracellular release of Ca2+ had not already been triggered by previous exposure to 3.0 mM Ca2+. This initial action was apparently followed by influx of Mn2+, since pronounced quenching of the fluorescence from the Ca2+ indicator fura-2 was observed. The results indicate that Mn2+ behaves in several respects like a calcium analogue in parathyroid cells and may inhibit PTH release by interfering directly with the secretory machinery.

Animals↗
PubMed1988

Diazoxide unmasks glucose inhibition of insulin release by counteracting entry of Ca2+.

The interaction of diazoxide with the effects of glucose on the insulin-releasing mechanism was analyzed in beta-cell-rich pancreatic islets isolated from ob/ob mice. When added at a concentration of 400 microM to a medium containing 1.28 mM Ca2+, diazoxide converted glucose stimulation of insulin release into inhibition. Further addition of 2 mM theophylline restored the insulin secretory response to glucose. The paradoxical glucose inhibition of insulin release was accounted for by a diazoxide interaction with the entry of Ca2+, unmasking a capacity of the sugar to lower cytoplasmic Ca2+ below its resting concentration.

Animals↗
PubMed1988

Hyperparathyroidism is associated with reduced expression of a parathyroid calcium receptor mechanism defined by monoclonal antiparathyroid antibodies.

Parathyroid tissue from patients with hyperparathyroidism (HPT) exhibited reduced immunohistochemical reactivity with monoclonal antiparathyroid antibodies, previously shown to stain intensely the surface of normal human parathyroid cells and to interfere with a receptor mechanism of these cells which is involved in the sensing and gating of Ca2+. Parathyroid hormone (PTH) release and cytoplasmic Ca2+ concentrations (Ca2+i) of dispersed cells from the pathological parathyroid glands had right-shifted dependencies on extracellular Ca2+, and exposure to the antibodies rendered both Ca2+i and PTH release almost completely insensitive to changes in ambient Ca2+. The results suggest that reduced expression of a parathyroid calcium receptor mechanism may be an important cause for the aberrant PTH release in HPT.

Adenoma↗
PubMed1988

Relationship between external and cytoplasmic calcium concentrations, parathyroid hormone release and weight of parathyroid glands in human hyperparathyroidism.

Parathyroid hormone (PTH) release and cytoplasmic calcium concentrations were investigated at ambient calcium concentrations of 0.5-3.0 mmol/l in dispersed parathyroid cells from 44 hypercalcaemic patients with primary or uraemic hyperparathyroidism (HPT). In comparison with parathyroid cells from adult cattle, release of PTH by human preparations was reduced and values of the ambient calcium concentration causing half-maximal inhibition of PTH release (median effective dose, ED50) were significantly increased. Half-maximal inhibition of PTH release was obtained with concentrations of cytoplasmic calcium almost identical to the concentrations of ionized calcium in the plasma of the individual patients. Cytoplasmic concentrations of calcium in the parathyroid cells were inversely related to release of PTH. Concentrations of cytoplasmic calcium were significantly lower in human than in bovine cells and the ED50 for ambient calcium increase on cytoplasmic calcium was raised to the same extent as the ED50 for ambient calcium inhibition of PTH release in human compared with bovine cells. The magnitude of the increased ED50 for ambient calcium inhibition of PTH release and increase of cytoplasmic calcium concentration was similar in adenomas and sporadic as well as hereditary primary hyperplasias, but the secretion was the least aberrant in uraemic hyperplasias, although they had by far the largest glandular mass. Serum concentrations of total calcium before surgery correlated with the ED50 for ambient calcium effects of PTH release and cytoplasmic calcium, but not with glandular weight. These findings demonstrate a universally abnormal regulation of cytoplasmic calcium in HPT and its importance for PTH release, and that disturbance of cytoplasmic calcium rather than the increased glandular mass contributes to the hypercalcaemia in adenomatous and hyperplastic HPT.

Calcium↗
PubMed1988

Inhibition of cell growth retains differentiated function of bovine parathyroid cells in monolayer culture.

Monolayer culture of bovine parathyroid cells for up to 4 days in medium containing 10% serum resulted in cell hypertrophy and proliferation as well as functional dedifferentiation. Compared to freshly isolated cells there was a right-shifted dose-effect relationship for calcium-inhibited parathyroid hormone (PTH) release, a decreased suppressibility of secretion and an inability of the cytoplasmic Ca2+ concentration (Ca2+i) to follow changes in the extracellular Ca2+ concentration. The functional changes seemed not to be due to culture per se, since human parathyroid cells exhibited an essentially unchanged regulation of Ca2+i even after 8 days of culture in 10% serum. During culture in medium containing 0.1% serum, the bovine cells did not proliferate and there was only slight cell hypertrophy. These cells retained much of their ability to regulate Ca2+i and PTH release. The results indicate that functional dedifferentiation of parathyroid cells is related to cell growth.

Animals↗
PubMed1988

Dimethyl sulfoxide inhibits proliferation but not hypertrophy and functional dedifferentiation of bovine parathyroid cells in culture.

Primary cultures of bovine parathyroid cells were used to study the relationship between parathyroid hormone (PTH) release, regulation of the cytoplasmic Ca2+ concentration (Ca2+i) and cell growth. Parathyroid cells were seeded into fibronectin-coated culture wells in the absence (control) or presence of 2% (v/v) dimethyl sulfoxide (DMSO). Both groups of cells attached and flattened out, and during 4 days of culture the cell diameters and protein content increased. However, whereas the number of cells in the control group increased by 60% and their 3H-thymidine incorporation tenfold, the DMSO cultured cells exhibited no signs of cell proliferation. Despite this difference in cell replication rate both groups of cells developed similar functional dedifferentiation. There was consequently a decreased Ca2+ suppressibility of PTH release, and Ca2+i did not follow the ambient Ca2+ concentration in a usual manner. It is concluded that during culture bovine parathyroid cells develop morphological and functional abnormalities similar those in parathyroid cells from patients with hyperparathyroidism. Moreover, this functional dedifferentiation could be dissociated from increased cell proliferation but may be related to cell hypertrophy.

Animals↗
PubMed1987

The actions of arginine and glucose on glucagon secretion are mediated by opposite effects on cytoplasmic Ca2+.

Cytoplasmic Ca2+ (Ca2+i) was monitored in single guinea-pig pancreatic alpha 2-cells exposed to modulators of glucagon release. The stimulatory amino acid arginine raised Ca2+i from 62 to 160 nM, whereas the inhibitor glucose reduced both the latter concentration and basal Ca2+i by 30%. Epinephrine which potentiates arginine-stimulated secretion by increasing cAMP, does so without affecting Ca2+i. The results indicate that glucagon secretion is positively modulated by Ca2+i. It is suggested that glucose-induced lowering of Ca2+i is a fundamental effect in cells where the sugar is readily metabolized.

Animals↗
PubMed1987

Dimethyl sulfoxide increases cytoplasmic Ca2+ concentration and inhibits parathyroid hormone release in normal bovine and pathological human parathyroid cells.

The acute effects of dimethyl sulfoxide (DMSO) on parathyroid hormone (PTH) release and the cytoplasmic Ca2+ concentration (Ca2+i) were studied in dispersed bovine cells and cells isolated from human parathyroid adenomas. At extracellular Ca2+ concentrations in the 0.5-3.0 mM range, but not at less than 25 nM, addition of 2% DMSO caused a rapid rise of Ca2+i. This effect corresponded to an inhibition of PTH release and there was a strong negative correlation between Ca2+i and secretion. The actions of DMSO on Ca2+i and PTH release were less pronounced in the pathological human cells. The data are consistent with a DMSO effect on the Ca2+-sensor function of the parathyroid cell, possibly mediated by an altered plasma membrane fluidity.

Adenoma↗
PubMed1987

Monoclonal anti-parathyroid antibodies interfering with a Ca2+-sensor of human parathyroid cells.

Previous findings indicate that binding of Ca2+ to an external receptor is part of the mechanism by which extracellular Ca2+ regulates cytoplasmic Ca2+ and hormone release of parathyroid cells. We now present evidence that two newly generated monoclonal anti-parathyroid antibodies react with structures involved in this sensing and/or gating of Ca2+. Microfluorimetric studies of fura 2-loaded human parathyroid cells thus revealed that the antibodies competed with Ca2+ and antagonized the rise in cytoplasmic Ca2+ normally obtained when parathyroid cells are exposed to increasing concentrations of extracellular Ca2+.

Antibodies, Monoclonal↗
PubMed1987

Bimodal regulation of secretion by cytoplasmic Ca2+ as demonstrated by the parathyroid.

Bovine parathyroid cells were used to study parathyroid hormone (PTH) release and the cytoplasmic Ca2+ concentration (Cai2+). When the extracellular Ca2+ concentration was decreased from 3.0 to 0.5 mM, perifused cells reacted with rapid stimulation of PTH release. However, a further reduction of extracellular Ca2+ to less than 10 nM resulted in prompt inhibition. Both effects were readily reversible. Using the intracellular Ca2+ indicator quin-2 also as a buffer for calcium it was possible to control Cai2+ within the 20-600 nM range. PTH release was found to increase with Cai2+ up to 200 nM but was gradually suppressed above this concentration.

Aminoquinolines↗
PubMed1987

Cytoplasmic Ca2+ concentration of single normal human and bovine parathyroid cells measured by dual wavelength microfluorometry.

Dual wavelength microfluorometry was utilized to measure the cytoplasmic calcium concentration (Cai2+) of single parathyroid cells loaded with the indicator fura-2. The method enabled the first registrations of Cai2+ of normal human parathyroid cells, available only in minute numbers. At 0.5 mM extracellular Ca2+, the Cai2+ levels were similar in normal human and bovine cells. Both cell types responded with an initial Cai2+ transient followed by a sustained increase when raising extracellular Ca2+ to 3.0 mM. The sustained effect exhibited a sigmoidal relation to extracellular Ca2+ in the 0.5-3.0 mM range. Although the increase was somewhat greater in the human cells, the half maximal responses were obtained at almost identical extracellular Ca2+ concentrations. Whereas K+ depolarization decreased Cai2+, the Ca2+ channel blocker D-600 had dual actions, raising Cai2+ at 0.5 mM Ca2+ and decreasing it at 3.0 mM Ca2+, and the effects were similar in the bovine and human cells. The present experimental approach verified the validity of utilizing bovine cells as controls in studies of human parathyroid tissue and it appears suitable for analysis of the role of different subpopulations of parathyroid cells in the abnormal parathyroid tissue of patients with hyperparathyroidism.

Animals↗
PubMed1987

TPA induces cytoplasmic alkalinization in human monoblastic U-937 cells without activation of Na+/H+ exchange.

The effect of the tumor-promoting phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) on cytoplasmic pH (pHi) and H+ extrusion was studied in the human monoblastic cell line U-937. About 2 min after addition of TPA, pHi started to increase and reached a steady state 10-15 min later. The resulting alkalinization corresponded to 0.03 and 0.09 pH units at 10(-10) and 10(-7) M TPA, respectively. The TPA-induced increase in pHi was independent of the presence of extracellular Na+. Moreover, TPA did not affect the H+ extrusion from the U-937 cells. Together these observations indicate the presence of a novel mechanism for TPA-induced cytoplasmic alkalinization. This mechanism is independent of Na+/H+ exchange across the plasma membrane, but may involve organelle sequestration of H+.

Carrier Proteins↗
PubMed1987

External ATP mimics carbachol in initiating calcium mobilization from pancreatic beta-cells conditioned by previous exposure to glucose.

1 Exposure to ATP (2-200 microM) resulted in a prominent peak of 45Ca efflux, when beta-cell-rich pancreatic islets from ob/ob-mice were perifused with a Ca2+-deficient medium. ADP and the stable alpha/beta-methylene analogues of ATP and ADP also had stimulatory effects. 2 The nucleotide initiation of 45Ca efflux mimicked that obtained with carbachol both in requiring previous exposure to glucose and in being more pronounced after replacing extracellular Na+ by K+. 3 It was possible to induce repeated peaks of stimulated 45Ca efflux, when the exposure to ATP was interrupted with intervals of perifusion with glucose-containing media. 4 The observations are consistent with the existence of P2-purinoceptors in islets, suggesting that these receptors mediate a similar mobilization of calcium as noted when activating polyphosphoinositide breakdown with carbachol. In view of the high contents of ATP and ADP in the beta-cell secretory granules, activation of P2-purinoceptors should be considered as a possible mechanism for amplification of the initial insulin secretory response.

Adenine Nucleotides↗
PubMed1987

Development of abnormal parathyroid cell function during monolayer culture and its relation to cellular hypertrophy and proliferation.

Primary cultures of adult bovine parathyroid cells grown for up to 8 days were used to study the relationship between regulation of parathyroid hormone (PTH) release, cytoplasmic Ca2+ (Ca2+i) and cell growth. Cell counting indicated that proliferation was inversely proportional to the seeding density. The culture was associated with cell enlargement without apparent relation to the proliferation rate. Moreover, flow cytometric analysis of the DNA distribution excluded that the hypertrophy was due to a high proportion of the cells being in the S and G2 stages of the cell cycle. With progressive time in culture there was a gradual deterioration of the ability of increasing concentrations of extracellular Ca2+ to suppress PTH secretion and raise Ca2+i. This functional dedifferentiation developed to the same extent despite considerable differences in proliferation rates. The data show that parathyroid cells in monolayer culture develop functional and some of the morphological characteristics of parathyroid cells from patients with hyperparathyroidism and that the functional abnormality seems to be related to hypertrophy but not to proliferation of the cells.

Animals↗
PubMed1986

Dual effects of a new hypocalcemic agent, WR-2721, on cytoplasmic Ca2+ and parathyroid hormone release of dispersed parathyroid cells from patients with hyperparathyroidism.

The effects of the new hypocalcemic agent, WR-2721, on calcium-regulated parathyroid hormone (PTH) release, cytoplasmic Ca2+ (Ca2+i) and membrane potential were measured in dispersed parathyroid cells from patients with hyperparathyrodisim (HPT). The drug had no effects in the absence of extracellular Ca2+ but acted synergistically with Ca2+ in the 0.5-1.5 mM range by depolarizing the cells, increasing Ca2+i and inhibiting PTH release. Although the depolarizing effect of 3.0 mM Ca2+ was unaffected by WR-2721 the drug antagonized the effect of Ca2+ by decreasing Ca2+i and stimulating PTH release. Whereas the inhibitory actions of WR-2721 on PTH release may result from the activation of the mechanism for Ca2+ gating in the parathyroid cell plasma membrane, the stimulatory effect probably reflects increased intracellular Ca2+ sequestration. The drug is considered potentially important for the treatment of HPT.

Amifostine↗
PubMed1986

Calcium-activated calcium permeability in parathyroid cells.

The Ca2+ receptor mechanism of the parathyroid cell was studied using La3+ as a probe. La3+ was found to bind to the cell surface without further penetration. Measurements of 45Ca fluxes and the cytoplasmic Ca2+ concentration (Ca2+i) revealed a stimulatory component in the action of La3+ on Ca2+ permeability resulting in a rise in Ca2+i. These effects mimicked those obtained when raising the extracellular Ca2+ concentration from 0.5 to 3.0 mM, but the actions of La3+ and Ca2+ were not additive. The results suggest the existence of a novel Ca2+ permeability physiologically activated by binding of Ca2+ to an external receptor.

Animals↗
PubMed1986

Glucose-stimulated sequestration of Ca2+ in clonal insulin-releasing cells. Evidence for an opposing effect of muscarinic-receptor activation.

Net fluxes of Ca2+ and acid production were studied in clonal insulin-releasing cells (RINm5F) by using colour indicators and dual-wavelength spectrophotometry. After equilibration with a medium containing 10-20 microM-Ca2+, only minimal amounts of Ca2+ (0.08 mmol/kg of protein) were released from the cells by subsequent additions of the respiratory blocker antimycin A and the Ca2+ ionophore A23187. The presence of 20 mM-glucose resulted in an almost 5-fold increase of the acid production and in a stimulated net uptake of Ca2+. The latter process was independent of the extracellular Ca2+ concentration and reached saturation after 20 +/- 1 min, when it corresponded to 1.18 +/- 0.07 mmol of calcium/kg of protein. Whereas the thiol reagent iodoacetamide suppressed the acid production, interference with mitochondrial function by using antimycin A or the uncoupler carbonyl cyanide m-chlorophenylhydrazone had the opposite effect. The latter two drugs induced a selective release of Ca2+ from a pool containing 35% of that taken up during glucose exposure. Most of the remaining Ca2+ was liberated by A23187 or iodoacetamide. Carbamoylcholine was also selective in mobilizing glucose-stimulated calcium, but this calcium (17%) appeared to originate from the pool insensitive to mitochondrial poisons. The action of carbamoylcholine was blocked by atropine and did not depend on the presence of extracellular Na+. The opposite effects of glucose and muscarinic-receptor activation on a non-mitochondrial calcium pool are consistent with participation of the endoplasmic reticulum in the glucose-induced sequestration of Ca2+ in pancreatic beta-cells.

Adenoma, Islet Cell↗