scholarly journals The membrane potential of human platelets

Blood ◽  
1983 ◽  
Vol 61 (1) ◽  
pp. 180-185 ◽  
Author(s):  
LT Friedhoff ◽  
M Sonenberg
Keyword(s):  
Membrane Potential ◽  
Calcium Ion ◽  
Human Platelet ◽  
Adenosine Diphosphate ◽  
Human Platelets ◽  
Ion Concentration ◽  
Extracellular Potassium ◽  
Ion Concentrations ◽  
Calcium Ion Concentration ◽  
Extracellular Sodium

Abstract The membrane potential of the human platelet was investigated using the membrane potential probes 3,3′-dipropyl-2,2′-thiadicarbocyanine iodide and tritiated triphenylmethylphosphonium bromide. The membrane potential in physiologic buffer was estimated to be 52–60 mV inside negative. The membrane was depolarized when extracellular potassium or hydrogen ion concentrations were increased. Changes in extracellular sodium, chloride, or calcium ion concentration had no measurable effect on membrane potential. Elevated extracellular potassium has been shown to increase platelet sensitivity to the aggregating agent, adenosine diphosphate. Our results show that changes in extracellular ion concentrations that depolarize platelets increase platelet sensitivity to aggregating agents. These results suggest that membrane potential changes may play a role in modulating the response of platelets to aggregating agents.

scholarly journals The membrane potential of human platelets

Blood ◽  
1983 ◽  
Vol 61 (1) ◽  
pp. 180-185
Author(s):  
LT Friedhoff ◽  
M Sonenberg
Keyword(s):  
Membrane Potential ◽  
Calcium Ion ◽  
Human Platelet ◽  
Adenosine Diphosphate ◽  
Human Platelets ◽  
Ion Concentration ◽  
Extracellular Potassium ◽  
Ion Concentrations ◽  
Calcium Ion Concentration ◽  
Extracellular Sodium

The membrane potential of the human platelet was investigated using the membrane potential probes 3,3′-dipropyl-2,2′-thiadicarbocyanine iodide and tritiated triphenylmethylphosphonium bromide. The membrane potential in physiologic buffer was estimated to be 52–60 mV inside negative. The membrane was depolarized when extracellular potassium or hydrogen ion concentrations were increased. Changes in extracellular sodium, chloride, or calcium ion concentration had no measurable effect on membrane potential. Elevated extracellular potassium has been shown to increase platelet sensitivity to the aggregating agent, adenosine diphosphate. Our results show that changes in extracellular ion concentrations that depolarize platelets increase platelet sensitivity to aggregating agents. These results suggest that membrane potential changes may play a role in modulating the response of platelets to aggregating agents.

scholarly journals Effect of calcium ion concentration on the ability of fibrinogen and von Willebrand factor to support the ADP-induced aggregation of human platelets

Blood ◽  
1987 ◽  
Vol 70 (3) ◽  
pp. 827-831 ◽  
Author(s):  
EJ Harfenist ◽  
MA Packham ◽  
RL Kinlough-Rathbone ◽  
M Cattaneo ◽  
JF Mustard
Keyword(s):  
Von Willebrand Factor ◽  
Calcium Ion ◽  
Human Platelets ◽  
Ion Concentration ◽  
Albumin Solution ◽  
High Calcium ◽  
Calcium Ion Concentration ◽  
Von Willebrand ◽  
Induced Aggregation ◽  
Willebrand Factor

Abstract To investigate the suggestion that von Willebrand factor (vWf) can substitute for fibrinogen in supporting ADP-induced aggregation of human platelets, we studied platelet reactions in two media: (1) a high calcium medium, Tyrode-albumin solution containing calcium ions in the physiological range of 2 mmol/L, and (2) a low calcium medium, modified Tyrode-albumin solution from which calcium salt was omitted (calcium ion concentration approximately 20 mumol/L). In the high calcium medium vWf even at concentrations up to six times as high as physiological, showed little or no potentiation of ADP-induced platelet aggregation, whereas fibrinogen strongly potentiated reversible aggregation without thromboxane formation or release of granule contents. In the low calcium medium, either vWf or fibrinogen supported biphasic aggregation in response to ADP, with thromboxane formation and release of granule contents. Aspirin and the thromboxane receptor blocker BM 13.177 inhibited these secondary responses to von Willebrand factor, indicating that they require thromboxane A2 formation and feedback amplification by thromboxane A2. A monoclonal antibody, 10E5, to the platelet glycoprotein IIb/IIIa complex inhibited both primary and secondary aggregation. Although vWf supports ADP-induced aggregation when the concentration of ionized calcium is in the micromolar range, it does not support ADP-induced aggregation in the presence of a concentration of ionized calcium in the physiological range, indicating that vWf probably cannot substitute for fibrinogen in supporting ADP- induced aggregation in vivo.

scholarly journals Oscillatory membrane potential changes in cells of mesenchymal origin: the role of an intracellular calcium regulating system

1979 ◽  
Vol 81 (1) ◽  
pp. 49-61
Author(s):  
P. G. Nelson ◽  
M. P. Henkart
Keyword(s):  
Endoplasmic Reticulum ◽  
Membrane Potential ◽  
Intracellular Calcium ◽  
Calcium Ion ◽  
Surface Membrane ◽  
Ion Concentration ◽  
Free Calcium ◽  
Potassium Ions ◽  
Calcium Ion Concentration

A number of mesenchymal cells (fibroblasts, macrophages and megakaryocytes) respond to a variety of stimuli with large hyperpolarizations lasting several seconds (the H.A. response). The H.A. responses can occur as repetitive trains or oscillations. These hyperpolarizations are due to an increase of the surface membrane permeability to potassium ions which is probably mediated by an increase in the cytoplasmic free calcium ion concentration. Evidence is discussed which suggests that the source of this increased calcium, is least in part, an intracellular sequestering system, probably the endoplasmic reticulum. A model capable of producing oscillatory changes in membrane potential is proposed based on such an intracellular calcium sequestering and releasing system.

Physiochemical Properties of Thermomycolase, the Thermostable, Extracellular, Serine Protease of the Fungus Malbranchea pulchella

1974 ◽  
Vol 52 (11) ◽  
pp. 981-990 ◽  
Author(s):  
Gerrit Voordouw ◽  
G. Maurice Gaucher ◽  
Rodney S. Roche
Keyword(s):  
Molecular Weight ◽  
Calcium Ion ◽  
Sodium Dodecyl ◽  
Sedimentation Coefficient ◽  
Ion Concentration ◽  
Sedimentation Equilibrium ◽  
Globular Structure ◽  
Ion Concentrations ◽  
Malbranchea Pulchella ◽  
Calcium Ion Concentration

The physicochemical properties of the extracellular protease of the fungus Malbranchea pulchella, for which we have adopted the name thermomycolase, were investigated. The molecular weight of diisopropylphosphorylthermomycolase was found to be 32 000–33 000 by sedimentation equilibrium and sodium dodecyl sulfate (SDS) gel electrophoresis. Its sedimentation coefficient (s020, w = 2.97 S), intrinsic viscosity ([η] = 3.0 cc/g), and frictional ratio (f/f0 = 1.09) characterize the enzyme as a typical globular protein. The circular dichroism spectrum of the protein is also consistent with its globular structure. Active thermomycolase autolyzes extensively, especially at low calcium ion concentrations, producing low molecular weight peptide material. In the presence of SDS, a different autolytic degradation is observed, resulting in much higher molecular weight polypeptide products (16 500, 12 500,11 000, 8 500). The results indicate that, in the presence of SDS, thermomycolase has three sites that are highly susceptible to autolysis. At calcium ion concentrations of 10−3 M and 10−2 M the enzyme undergoes a sharp thermal denaturation with transition temperatures at 69 °C and 75 °C, respectively, and with complete loss of enzyme activity. At 70 °C the enzyme appeared to be maximally thermostable at a calcium ion concentration of 10−2 M.

scholarly journals Effect of calcium ion concentration on the ability of fibrinogen and von Willebrand factor to support the ADP-induced aggregation of human platelets

Blood ◽  
1987 ◽  
Vol 70 (3) ◽  
pp. 827-831 ◽  
Author(s):  
EJ Harfenist ◽  
MA Packham ◽  
RL Kinlough-Rathbone ◽  
M Cattaneo ◽  
JF Mustard
Keyword(s):  
Von Willebrand Factor ◽  
Calcium Ion ◽  
Human Platelets ◽  
Ion Concentration ◽  
Albumin Solution ◽  
High Calcium ◽  
Calcium Ion Concentration ◽  
Von Willebrand ◽  
Induced Aggregation ◽  
Willebrand Factor

To investigate the suggestion that von Willebrand factor (vWf) can substitute for fibrinogen in supporting ADP-induced aggregation of human platelets, we studied platelet reactions in two media: (1) a high calcium medium, Tyrode-albumin solution containing calcium ions in the physiological range of 2 mmol/L, and (2) a low calcium medium, modified Tyrode-albumin solution from which calcium salt was omitted (calcium ion concentration approximately 20 mumol/L). In the high calcium medium vWf even at concentrations up to six times as high as physiological, showed little or no potentiation of ADP-induced platelet aggregation, whereas fibrinogen strongly potentiated reversible aggregation without thromboxane formation or release of granule contents. In the low calcium medium, either vWf or fibrinogen supported biphasic aggregation in response to ADP, with thromboxane formation and release of granule contents. Aspirin and the thromboxane receptor blocker BM 13.177 inhibited these secondary responses to von Willebrand factor, indicating that they require thromboxane A2 formation and feedback amplification by thromboxane A2. A monoclonal antibody, 10E5, to the platelet glycoprotein IIb/IIIa complex inhibited both primary and secondary aggregation. Although vWf supports ADP-induced aggregation when the concentration of ionized calcium is in the micromolar range, it does not support ADP-induced aggregation in the presence of a concentration of ionized calcium in the physiological range, indicating that vWf probably cannot substitute for fibrinogen in supporting ADP- induced aggregation in vivo.

Dissociation of membrane potential and hormone secretion in bovine parathyroid cells

1983 ◽  
Vol 245 (1) ◽  
pp. E102-E105
Author(s):  
J. J. Morrissey ◽  
S. Klahr
Keyword(s):  
Parathyroid Hormone ◽  
Membrane Potential ◽  
Cell Membrane ◽  
Calcium Ion ◽  
Cell Function ◽  
Hormone Secretion ◽  
Ion Concentration ◽  
Parathyroid Cell ◽  
High Potassium ◽  
Calcium Ion Concentration

An increase in the calcium ion concentration of the medium from 0.5 to 2.0 mM is associated with a 65% decrease in the secretion of parathyroid hormone from dispersed parathyroid cells. This maneuver also depolarized the cell membrane from -55 to -21 mV as measured by the distribution of [3H]tetraphenylphosphonium ion between cells and medium. An increase in the potassium ion concentration of the medium to 50 mM caused a 67% increase in hormone secretion at 0.5 mM calcium and depolarized the cell to -31 mV. The high potassium did not significantly change hormone secretion or the membrane potential at 2.0 mM calcium. Chlorpromazine inhibited hormone secretion by 40% and depolarized the cell to -30 mV at 0.5 mM calcium in the medium. Chlorpromazine did not change hormone secretion or membrane potential in cells incubated at 2.0 mM calcium. These results suggest that depolarization of the cell by calcium cannot account by itself for the inhibition of hormone secretion and chlorpromazine mimics the effect of an increase in calcium on parathyroid cell function.

scholarly journals Regional Imaging of Brain Tissue Calcium Ions Using Aequorin

1992 ◽  
Vol 12 (2) ◽  
pp. 306-310 ◽  
Author(s):  
Kenji Hashimoto ◽  
Haruhiko Kikuchi ◽  
Masatsune Ishikawa ◽  
Shuichi Kobayashi
Keyword(s):  
Linear Relationship ◽  
Spatial Resolution ◽  
Calcium Ions ◽  
Calcium Ion ◽  
High Spatial Resolution ◽  
Ion Concentration ◽  
Ion Distribution ◽  
Ion Concentrations ◽  
Tissue Calcium ◽  
Calcium Ion Concentration

To investigate regional changes in calcium ion concentrations, we developed a new histochemical method using aequorin, a calcium ion-sensitive photoprotein. In this method, reagent film containing aequorin was made and an unfixed slice of frozen brain 16 μm thick was placed on it. Tissue calcium ions permeated the reagent layer and the bioluminescence of aequorin-calcium ions was recorded photographically with high spatial resolution. There was a close linear relationship ( r = 0.903) between the optical density of the bioluminescent images and the logarithmic values of the tissue calcium ion concentration. Using this method, we could visualize the regional tissue calcium ion distribution in pathological states in rat brains.

The Sensitivity Shift Due to Light Adaptation Depending on the Extracellular Calcium Ion Concentration in Limulus Ventral Nerve Photoreceptor

1984 ◽  
Vol 39 (6) ◽  
pp. 662-679 ◽  
Author(s):  
H. Stieve ◽  
M. Bruns ◽  
H. Gaube
Keyword(s):  
Calcium Ion ◽  
Light Adaptation ◽  
Light Response ◽  
Ion Concentration ◽  
Ion Concentrations ◽  
Intracellular Ca ◽  
Calcium Effect ◽  
Calcium Ion Concentration ◽  
Additional Reduction ◽  
Ventral Nerve Photoreceptor

Receptor potentials of Limulus ventral photoreceptors were recorded in two defined states of moderate light- and considerable dark adaptation (LA, DA) by a repeated stimulus sequence consisting of a conditioning 2 s illumination (white light, response saturating intensity) followed by two 10 ms test flashes at fixed intervals evoking LA and DA responses (intensity varied from threshold to saturation of response amplitude). The half saturating intensity I50 was determined from response height vs log stimulus intensity curves for LA and DA, while the photoreceptor was superfused either by reference saline (physiological ion concentrations, including 10 mmol/l Ca2+) or by test salines in which the [Ca2+] was varied between 40 μmol/l and 100 mmol/l. The sensitivity of the dark-adapted receptor does not significantly depend on the [Ca2+]ex, but the sensitivity shift due to LA (measured by /50) is reduced when the [Ca2+]ex is lowered, and augmented when the [Ca2+]ex is increased. Additional reduction of the [Na2+]ex from 463 mmol/l to 46 mmol/l or increase of the [Mg2+]ex from 50 mmol/l to 100 mmol/l does not counteract the effect of lowered [Ca2+]ex on LA. The results confirm the assumption that a transient increase of the intracellular [Ca2+] supplied from extracellular sources during the light response is the main cause for LA This calcium effect on light adaptation is neither characterized by a calcium/sodium antagonism, nor mimicked by magnesium, in contrast to the calcium effect on the gating of the light-activated ion channels.

scholarly journals Cytosolic free calcium-ion concentration in cleaving embryonic cells of Oryzias latipes measured with calcium-selective microelectrodes.

1985 ◽  
Vol 100 (3) ◽  
pp. 947-954 ◽  
Author(s):  
A R Schantz
Keyword(s):  
Membrane Potential ◽  
Calcium Ion ◽  
Oryzias Latipes ◽  
Potassium Acetate ◽  
Ion Concentration ◽  
Free Calcium ◽  
Embryonic Cells ◽  
Cell Stage ◽  
Partial Digestion ◽  
Calcium Ion Concentration

Calcium-selective microelectrodes were used to measure the free calcium-ion concentration ([Ca2+]i) in early-cleaving embryonic cells of the golden medaka, Oryzias latipes, a fresh water teleost fish. Embryos could be dechorionated as early as the four-cell stage using a three-step technique consisting of removal of some yolk to enlarge the perivitelline space, partial digestion of the chorion with pancreatin, and removal of the weakened chorion with forceps. Dechorionated embryos underwent cleavage at a normal rate. Intracellular cytosolic [Ca2+]i was monitored by impaling blastomeres first with a microelectrode filled with 5 M potassium acetate to measure membrane potential, and a few minutes later with a calcium-selective microelectrode. During nine rounds of cytokinesis from a total of six different embryos, cytosolic [Ca2+]i remained constant (with apparently random fluctuations of less than +/- 0.1 microM). During two successive cleavages in one embryo, however, [Ca2+]i rose transiently fourfold above the original resting level to 1.32 and 1.20 microM in synchrony with each period of cytokinesis and returned after each rise to submicromolar levels. Because a calcium-selective microelectrode can detect [Ca2+]i changes only in the immediate vicinity of its 2-microns tip, we interpreted these data to suggest that, although [Ca2+]i in most areas of the cytosol remains between 0.01 and 0.40 microM (mean of 0.14 microM), there may be small regions of the cell in which [Ca2+]i undergoes a substantial increase at the time of cleavage. Evidence also is presented to suggest that the membrane potential in these blastomeres undergoes a slow net hyperpolarization during early cleavage stages.

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