Further characterization of calcium-accumulating vesicles from human blood platelets

Käser-Glanzmann, R.; Jakábová, Milica; George, JN; Lüscher, E. F.

doi:10.1016/0005-2736(78)90213-4

Cited by 58 publications

(15 citation statements)

References 32 publications

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“…The final concentration of organic solvent was always below 0.5%. cAMP does not lower the resting intracellular Ca 2+ concentration by stimulation of mechanisms such as Ca 2+ extrusion or Ca 2+ sequestration in intracellular compartments, as proposed in [10]. Increasing concentrations of the Ca z+ ionophore ionomycin produced cells with progressively increased levels of Ca 2+ which were maintained at a steady level for at least 3 min after stimulation.…”

Section: Methodsmentioning

confidence: 89%

cAMP reduces the affinity of Ca²⁺‐triggered secretion in platelets

Collazos

Sánchez

1987

FEBS Letters

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Prostacyclin and other related compounds known to increase intracellular cAMP levels inhibit platelet responses. The mechanisms involved are only partially known, especially those concerning the complex relations between Ca 2 ÷ and cAMP as opposite intracellular mediators. Here, we have investigated aggregation and secretion in quin2-1oaded platelets under conditions in which Ca 2 ÷ and cAMP are the only intracellular mediators. Our results show that cAMP inhibits aggregation and secretion in ionophore-treated cell without modifying their intracellular Ca 2 + levels. This result suggests that the inhibition takes place on some intracellular target for Ca 2 +. cyclic AMP; Ionomycin; Secretion; Piatelet; intracellular Ca 2 +

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Section: Methodsmentioning

confidence: 89%

cAMP reduces the affinity of Ca²⁺‐triggered secretion in platelets

Collazos

Sánchez

1987

FEBS Letters

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“…3a); however, tBHQ inhibition was significantly enhanced by Mg2+ in both cases. Since Mg2+ facilitates the dephosphorylation of the Ca2+-pump phosphoenzyme intermediate, this indicates that tBHQ interferes with the autophosphorylation step of the catalytic cycle of Ca2+ pumps, rather than inhibiting dephosphorylation, as observed in La3+ inhibition, which blocks the enzyme in the phosphorylated state [34]. However, these data taken together suggest that the different Ca2+-pump isoforms have different sensitivities toward inhibition of phosphoenzyme formation by tBHQ, with sensitivity increasing in the order of smooth muscle < cardiac < skeletal muscle < platelet 97 kDa Ca2+-pump form.…”

Section: Vol 288mentioning

confidence: 99%

“…Platelet microsomal membrane vesicles were prepared as in [17,34]. Cardiacand skeletal-muscle sarcoplasmic-reticulum microsomal fractions were isolated as described in [35,36].…”

Section: Cell Membrane Preparationmentioning

confidence: 99%

Simultaneous presence of two distinct endoplasmic-reticulum-type calcium-pump isoforms in human cells. Characterization by radio-immunoblotting and inhibition by 2,5-di-(t-butyl)-1,4-benzohydroquinone

Papp

Enyedi

Pászty

et al. 1992

Biochemical Journal

105

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Phosphorylation, immunoblotting, limited proteolysis and drug-sensitivity analysis were used to characterize the sarcoendoplasmic-reticulum Ca2+ ATPases in a variety of human cell types. In platelets, several megakaryoblastoid and lymphoblastoid cell lines two distinct autophosphorylated forms of these ATPases with molecular mass of 100 and 97 kDa could be observed, whereas in several other cell types the 97 kDa form was absent. On immunoblots the 97 kDa species was specifically recognized by an inhibitory monoclonal antibody raised against the Ca2+ pump of platelet internal membranes, yielded on trypsinolysis a major fragment of 80 kDa, exhibited a distinct electrophoretic migration pattern as compared with the skeletal-, cardiac- and smooth-muscle Ca2+ pumps, and its autophosphorylation was strongly inhibited by the Ca(2+)-mobilizing agent 2,5-di-(t-butyl)-1,4-benzohydroquinone (tBHQ). The 100 kDa species reacted with an antibody specific for the cardiac- and smooth-muscle Ca2+ pumps, yielded on trypsinolysis fragments of 55 and 35 kDa, and its autophosphorylation was much less sensitive to tBHQ inhibition. These findings indicate the simultaneous presence of two different endoplasmic-reticulum Ca2+ pumps in a variety of human cell types, and may explain the previously observed differences in the Ca(2+)-handling characteristics of different intracellular Ca2+ pools and cell types.

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“…The different time course of the two responses is consistent with their proposed relationship since the observed [Ca"], is, in the absence of extracellular Ca2+, a product of processes which mobilise this cation from intracellular stores and which remove Ca2+ from the cytosol. If an increase in platelet [cyclic AMP] activates a Ca2+, Mg2+-ATPase ('Ca2+ pump') [34] the failure of prostaglandin D2 to reverse the decrease in chlortetracycline fluorescence induced by thrombin (Fig. 2) suggests that removal of Ca2+ by this pump is to a site, such as the extracellular fluid, which is not monitored by chlortetracycline thus suggesting that Ca2 (Fig.…”

Section: Discussionmentioning

confidence: 99%

Intracellular calcium fluxes in human platelets

Thompson

Scrutton

1985

European Journal of Biochemistry

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1. Fluorescence changes and secretory responses have been measured on addition of various excitatory agonists to platelets loaded with the cytosolic Ca2+ probe, Quin 2 or with chlortetracycline as a probe for membraneassociated Ca2+.2. When extracellular [Ca"] is decreased to less than 0.1 pM by addition of EGTA a linear correlation is observed between the extent of increase in cytosolic [Ca2 ' 1 and the extent of mobilisation of membrane-associated 3. Similar ECS0 values are observed for ATP secretion, the increase in cytosolic [Ca"] and the decrease in chlortetracycline fluorescence induced by thrombin. However, the decrease in chlortetracycline fluorescence shows a sigmoidal relationship with the increase in cytosolic [Ca2+] and a hyperbolic relationship with ATP secretion over this dose/response curve.4. Addition of prostaglandin D2 prior to thrombin causes parallel inhibition of the increase in cytosolic [Ca2+] and the decrease in chlortetracycline fluorescence induced by this agonist. However, addition of prostaglandin D2 after thrombin reverses the increase in cytosolic [Ca"] induced by this agonist but fails to cause a similar reversal of the decrease in chlortetracycline fluorescence.5. The data provide further evidence supporting the proposal that chlortatracycline can be used as a probe to monitor mobilisation of membrane-associated Ca2+ but suggest that, in platelets stimulated in the effective absence of extracellular Ca2+, both Ca2 + mobilisation and Ca2 + removal can under some conditions involve sites which are not monitored by this probe.It is generally accepted that changes in the cytosolic Ca2+ concentration ([Ca2+Ii) form an important part of the stimulus-response coupling pathway in human platelets [1] as in many other cells [2]. In platelets the Ca2+ ions required to sustain an increase in [Ca2+Ii can originate either from the extracellular fluid or from one or more intracellular pools [3 -51. The contribution of such intracellular pool(s) to the increase in [Ca2+Ii induced by several excitatory agonists, e.g. thrombin, can be demonstrated by observing increases in fluorescence from intracellularly trapped Quin 2 in the presence of EGTA as an extracellular Ca2+ chelating agent is, 61.Several storage sites exist within the platelet from which Ca2+ could be released to the cytosol including the dense tubular system, the amine storage granules and the mitochondria as well as a putative Ca2+ pool associated with the plasma membrane. Ca2+ sequestered in the amine storage granules does not appear to be in equilibrium with that present in the cytosol but rather is released to the extracellular fluid as a consequence of exocytosis following cellular activation [7 -91. Furthermore the decrease in chlortetracycline fluorescence induced by thrombin occurs more rapidly than the secretory response monitored as release of Ca2+ [3]. Although Ca2+ release can occur from mitochondria in vitro the conditions required to achieve such release do not appear compatible with participation in events at the time ...

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Further characterization of calcium-accumulating vesicles from human blood platelets

Cited by 58 publications

References 32 publications

cAMP reduces the affinity of Ca²⁺‐triggered secretion in platelets

cAMP reduces the affinity of Ca²⁺‐triggered secretion in platelets

Simultaneous presence of two distinct endoplasmic-reticulum-type calcium-pump isoforms in human cells. Characterization by radio-immunoblotting and inhibition by 2,5-di-(t-butyl)-1,4-benzohydroquinone

Intracellular calcium fluxes in human platelets

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Further characterization of calcium-accumulating vesicles from human blood platelets

Cited by 58 publications

References 32 publications

cAMP reduces the affinity of Ca2+‐triggered secretion in platelets

cAMP reduces the affinity of Ca2+‐triggered secretion in platelets

Simultaneous presence of two distinct endoplasmic-reticulum-type calcium-pump isoforms in human cells. Characterization by radio-immunoblotting and inhibition by 2,5-di-(t-butyl)-1,4-benzohydroquinone

Intracellular calcium fluxes in human platelets

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cAMP reduces the affinity of Ca²⁺‐triggered secretion in platelets

cAMP reduces the affinity of Ca²⁺‐triggered secretion in platelets