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Title: Modulation of cytosolic free calcium levels by extracellular phosphate and lanthanum

Abstract

The effects of extracellular phosphate and lanthanum on cytosolic free Ca/sup 2 +/ ((Ca/sup 2 +/)/sub i/) levels were studied in isolated rat pancreatic acini. In the presence of 1.28 mM Ca/sup 2 +/ and 1.0 mM phosphate, the mean resting (Ca/sup 2 +/)/sub i/ level was 120 nM. Omission of phosphate from incubation medium significantly lowered this value to 94 nM. The gastrointestinal hormone cholecystokinin octapeptide (CCK-8) rapidly enhanced both (Ca/sup 2 +/)/sub i/ levels and /sup 45/Ca/sup 2 +/ efflux, irrespective of the presence or absence of phosphate. Lanthanum (0.1 mM), a compound known to block transmembrane Ca/sup 2 +/ fluxes, attenuated both actions of CCK-8, but only in the absence of extracellular phosphate. There was a concomitant decrease in amylase secretion induced by 0.1 nM CCK-8 but not by 10 nM CCK-8, without a significant change in cellular ATP levels. The inhibitory actions of lanthanum on CCK-8-stimulated (Ca/sup 2 +/)/sub i/ levels were very rapid and were mimicked only by prolonged incubation of acini in Ca/sup 2 +/-free medium supplemented with EGTA. Omission of phosphate from incubation medium also lowered basal (Ca/sup 2 +/)/sub i/ levels in IM-9 lymphocytes. These findings suggest that extracellular phosphate may modulatemore » resting (Ca/sup 2 +/)/sub i/ levels in pancreatic acini and other cell types and that mobilization of intracellular Ca/sup 2 +/ may partly depend on the availability of a lanthanum-sensitive pool of cell-surface Ca/sup 2 +/ that is not readily removed by EGTA.« less

Authors:
;
Publication Date:
Research Org.:
Univ. of Arizona, Tucson
OSTI Identifier:
6372501
Resource Type:
Journal Article
Resource Relation:
Journal Name: Proc. Natl. Acad. Sci. U.S.A.; (United States); Journal Volume: 84:5
Country of Publication:
United States
Language:
English
Subject:
59 BASIC BIOLOGICAL SCIENCES; 63 RADIATION, THERMAL, AND OTHER ENVIRON. POLLUTANT EFFECTS ON LIVING ORGS. AND BIOL. MAT.; CALCIUM 45; MEMBRANE TRANSPORT; LANTHANUM; BIOCHEMISTRY; SODIUM PHOSPHATES; AMYLASE; CALCIUM COMPOUNDS; CATIONS; LYMPHOCYTES; METABOLIC DISEASES; PANCREAS; RATS; SODIUM CHLORIDES; ALKALI METAL COMPOUNDS; ALKALINE EARTH ISOTOPES; ALKALINE EARTH METAL COMPOUNDS; ANIMAL CELLS; ANIMALS; BETA DECAY RADIOISOTOPES; BETA-MINUS DECAY RADIOISOTOPES; BIOLOGICAL MATERIALS; BLOOD; BLOOD CELLS; BODY; BODY FLUIDS; CALCIUM ISOTOPES; CHARGED PARTICLES; CHEMISTRY; CHLORIDES; CHLORINE COMPOUNDS; CONNECTIVE TISSUE CELLS; DAYS LIVING RADIOISOTOPES; DIGESTIVE SYSTEM; DISEASES; ELEMENTS; ENDOCRINE GLANDS; ENZYMES; EVEN-ODD NUCLEI; GLANDS; GLYCOSYL HYDROLASES; HALIDES; HALOGEN COMPOUNDS; HYDROLASES; INTERMEDIATE MASS NUCLEI; IONS; ISOTOPES; LEUKOCYTES; MAMMALS; MATERIALS; METALS; NUCLEI; O-GLYCOSYL HYDROLASES; ORGANS; OXYGEN COMPOUNDS; PHOSPHATES; PHOSPHORUS COMPOUNDS; RADIOISOTOPES; RARE EARTHS; RODENTS; SODIUM COMPOUNDS; SOMATIC CELLS; VERTEBRATES; 550301* - Cytology- Tracer Techniques; 560300 - Chemicals Metabolism & Toxicology

Citation Formats

Korc, M., and Schoeni, M.H. Modulation of cytosolic free calcium levels by extracellular phosphate and lanthanum. United States: N. p., 1987. Web. doi:10.1073/pnas.84.5.1282.
Korc, M., & Schoeni, M.H. Modulation of cytosolic free calcium levels by extracellular phosphate and lanthanum. United States. doi:10.1073/pnas.84.5.1282.
Korc, M., and Schoeni, M.H. 1987. "Modulation of cytosolic free calcium levels by extracellular phosphate and lanthanum". United States. doi:10.1073/pnas.84.5.1282.
@article{osti_6372501,
title = {Modulation of cytosolic free calcium levels by extracellular phosphate and lanthanum},
author = {Korc, M. and Schoeni, M.H.},
abstractNote = {The effects of extracellular phosphate and lanthanum on cytosolic free Ca/sup 2 +/ ((Ca/sup 2 +/)/sub i/) levels were studied in isolated rat pancreatic acini. In the presence of 1.28 mM Ca/sup 2 +/ and 1.0 mM phosphate, the mean resting (Ca/sup 2 +/)/sub i/ level was 120 nM. Omission of phosphate from incubation medium significantly lowered this value to 94 nM. The gastrointestinal hormone cholecystokinin octapeptide (CCK-8) rapidly enhanced both (Ca/sup 2 +/)/sub i/ levels and /sup 45/Ca/sup 2 +/ efflux, irrespective of the presence or absence of phosphate. Lanthanum (0.1 mM), a compound known to block transmembrane Ca/sup 2 +/ fluxes, attenuated both actions of CCK-8, but only in the absence of extracellular phosphate. There was a concomitant decrease in amylase secretion induced by 0.1 nM CCK-8 but not by 10 nM CCK-8, without a significant change in cellular ATP levels. The inhibitory actions of lanthanum on CCK-8-stimulated (Ca/sup 2 +/)/sub i/ levels were very rapid and were mimicked only by prolonged incubation of acini in Ca/sup 2 +/-free medium supplemented with EGTA. Omission of phosphate from incubation medium also lowered basal (Ca/sup 2 +/)/sub i/ levels in IM-9 lymphocytes. These findings suggest that extracellular phosphate may modulate resting (Ca/sup 2 +/)/sub i/ levels in pancreatic acini and other cell types and that mobilization of intracellular Ca/sup 2 +/ may partly depend on the availability of a lanthanum-sensitive pool of cell-surface Ca/sup 2 +/ that is not readily removed by EGTA.},
doi = {10.1073/pnas.84.5.1282},
journal = {Proc. Natl. Acad. Sci. U.S.A.; (United States)},
number = ,
volume = 84:5,
place = {United States},
year = 1987,
month = 3
}
  • An array of techniques can be used to study cell calcium metabolism that comprises several calcium compartments and many types of transport systems such as ion channels, ATP-dependent pumps, and antiporters. The measurement of total call calcium brings little information of value since 60 to 80% of total cell calcium is actually bound to the extracellular glycocalyx. Cell fractionation and differential centrifugation have been used to study intracellular Ca{sup 2+} compartmentalization, but the methods suffer from the possibility of Ca{sup 2+} loss or redistribution among cell fractions. Steady-state kinetic analyses of {sup 45}Ca uptake or desaturation curves have been usedmore » to study the distribution of Ca{sup 2+} among various kinetic pools in living cells and their rate of Ca{sup 2+} exchange, but the analyses are constrained by many limitations. Nonsteady-state tracer studies can provide information about rapid changes in calcium influx or efflux in and out of the cell. Zero-time kinetics of {sup 45}Ca uptake can detect instantaneous changes in calcium influx, while {sup 45}Ca fractional efflux ratio, can detect rapid stimulations or inhibitions of calcium efflux out of cells. The best strategy to study cell calcium metabolism is to use several different methods that focus on a specific problem from widely different angles.« less
  • Two isozymes of 3-deoxy-D-arabin0-heptulosonate 7-phosphate synthase are partitioned into plastic (DS-Mn) and cytosolic (DS-Co) compartments of at least several higher plants. Differential variation of isozyme levels and in the timing of their expression was observed during growth of Nicotiana silvestris in suspension culture. The ratio of DS-Co to DS-Mn varied about fivefold in comparison of the different physiological stages of growth. Cultures maintained in exponential phase for >10 generations (EE cells) possessed balanced-growth properties and did not exhibit the considerable variation of isozyme levels found during the initial 2 to 3 generations of exponential growth (E cells) that followed subculturemore » of stationary-phase cultures. The plastid isozyme level declined substantially in stationary phase, responded immediately to subculture, and reached a peak in early exponential growth similar to the steady-state level of DS-Mn in EE cells. In contrast, the cytosolic isozyme level peaked in late exponential growth. A recent history of stationary-phase physiology appeared to foster elevated synthesis of DS-Co since the steady-state level of DS-Co in EE cells was much lower than in E cells.« less
  • Cytosolic free Ca2+ concentration ((Ca2+)i) was measured in normal rat pancreatic islet cells using the intracellular Ca2+ indicator fura 2. Glucose induced an initial decrease followed by a secondary rise in (Ca2+)i. The secondary rise probably resulted from an increase in Ca2+ inflow into the cells, while the initial decrease displayed several characteristics of the well known initial decrease in /sup 45/Ca efflux induced by glucose in prelabelled pancreatic islets. It is concluded that glucose may exert both an inhibitory and a stimulatory effect on (Ca2+)i in normal isolated islet cells.
  • We were able to purify two distinct sodium pump inhibitors to homogeneity from human urine based on ({sup 3}H)ouabain-displacing activity from intact human erythrocytes. The polar and less polar compounds were eluted off the C18 reverse-phase column with 18% and 31% acetonitrile, respectively. The polar compound cross-reacted very weakly with specific antidigoxin antibody and lacked a characteristic ultraviolet absorption peak between 190 and 300 nm. The less polar compound showed a prominent digoxinlike immunoreactivity and had an ultraviolet spectrum similar to that of digoxin. We examined the effects of these compounds on cytosolic free calcium concentration in cultured rat vascularmore » smooth muscle cells (A10 cells) using the fluorescent calcium chelator fura-2. Only the polar ouabain-displacing compound caused a significant increase, from 108 +/- 7 to 162 +/- 8 nM (n = 6, p less than 0.01), in cytosolic free calcium concentration in A10 cells. The rise in cytosolic free calcium concentration induced by the polar ouabain-displacing compound tended to be slower in onset and more sustained than that induced by arginine vasopressin. In contrast, ouabain and bufalin had no appreciable effects on cytosolic free calcium concentration in A10 cells. These results suggest that the polar ouabain-displacing compound we isolated from human urine may possess a vasoactive property and may play an important role in the modulation of vascular tone.« less
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