scholarly journals Pharmacology of a Ca2+-influx pathway activated by emptying the intracellular Ca2+ stores in HL-60 cells: evidence that a cytochrome P-450 is not involved

1994 ◽  
Vol 302 (1) ◽  
pp. 187-190 ◽  
Author(s):  
B D Koch ◽  
G F Faurot ◽  
M V Kopanitsa ◽  
D C Swinney
Keyword(s):  
Plasma Membrane ◽  
Selective Inhibitors ◽  
High Affinity ◽  
Voltage Dependent ◽  
Influx Pathways ◽  
Subsequent Activation ◽  
Cytochrome P 450 ◽  
Haem Iron ◽  
Dependent Pathway ◽  
Ca2 Channels

In HL-60 cells, inhibition of the endoplasmic-reticular Ca2+ pump by thapsigargin leads to the emptying of this intracellular Ca2+ store and a subsequent activation of plasma-membrane Ca2+ influx through a non-voltage-dependent pathway. The elevated intracellular free Ca2+ concentration ([Ca2+]i) produced and maintained by this Ca2+ inflow was used to examine the potency of various compounds to inhibit this influx mechanism. As expected, specific blockers of known Ca2+ channels, such as nifedipine, omega-conotoxin GVIA and ryanodine were without effect. The less selective inhibitors La3+, SKF-96365 and L-651,582, which are thought to inhibit both voltage-dependent and voltage-independent Ca2+ channels, decreased [Ca2+]i back to resting levels, with pIC50 values of 5.2, 5.9 and 6.2 respectively. It has been proposed that a cytochrome P-450 is involved in activating Ca(2+)-influx pathways in thymocytes, neutrophils and platelets. Consistent with this idea, the imidazole cytochrome P-450 inhibitors miconazole, econazole, clotrimazole and ketoconazole inhibited the thapsigargin-elevated [Ca2+]i with pIC50 values of 7.1, 7.1, 7.1 and 5.8 respectively. The high affinity of imidazoles for cytochromes P-450 is due to co-ordinate binding to the haem. This interaction is greatly decreased in 2-substituted imidazoles. We examined whether the inhibition of Ca2+ influx was due to an interaction of the inhibitor imidazole nitrogen with the haem iron of the putative cytochrome P-450 by comparing the activity of two compounds, identical except that one was methylated at the imidazole 2-position. They were found to block thapsigargin-activated Ca2+ influx with equal potency. These results strongly suggest that a cytochrome P-450 is not involved in the activation of the Ca2+ influx produced by emptying the intracellular Ca2+ stores.

scholarly journals Calcium efflux and cycling across the synaptosomal plasma membrane

1985 ◽  
Vol 226 (1) ◽  
pp. 225-231 ◽  
Author(s):  
R Snelling ◽  
D Nicholls
Keyword(s):  
Plasma Membrane ◽  
Steady State ◽  
Potential Gradient ◽  
Electrochemical Potential ◽  
Electrochemical Gradient ◽  
Calcium Efflux ◽  
Normal Medium ◽  
Voltage Dependent ◽  
Synaptosomal Plasma Membrane ◽  
Ca2 Channels

Ca2+ efflux from intact synaptosomes is investigated. Net efflux can be induced by returning synaptosomes from media with elevated Ca2+ or high pH to a normal medium. Net Ca2+ efflux is accelerated when the Na+ electrochemical potential gradient is collapsed by veratridine plus ouabain. Under steady-state conditions at 30 degrees C, Ca2+ cycles across the plasma membrane at 0.38 nmol . min-1 . mg-1 of protein. Exchange is increased by 145% by veratridine plus ouabain, both influx and efflux being increased. Increased influx is probably due to activation of voltage-dependent Ca2+ channels, since it is abolished by verapamil. The results indicate that, at least under conditions of low Na+ electrochemical gradient, some pathway other than a Na+/Ca2+ exchange must operate in the plasma membrane to expel Ca2+.

scholarly journals Mechanisms and Physiological Significance of the Cholinergic Control of Pancreatic β-Cell Function

2001 ◽  
Vol 22 (5) ◽  
pp. 565-604 ◽  
Author(s):  
Patrick Gilon ◽  
Jean-Claude Henquin
Keyword(s):  
Plasma Membrane ◽  
Cell Function ◽  
Β Cells ◽  
Insulin Granules ◽  
M3 Receptors ◽  
Voltage Dependent ◽  
Β Cell Function ◽  
Insulinotropic Effect ◽  
Ca2 Channels ◽  
Glucose Dependence

Abstract Acetylcholine (ACh), the major parasympathetic neurotransmitter, is released by intrapancreatic nerve endings during the preabsorptive and absorptive phases of feeding. In β-cells, ACh binds to muscarinic M3 receptors and exerts complex effects, which culminate in an increase of glucose (nutrient)-induced insulin secretion. Activation of PLC generates diacylglycerol. Activation of PLA2 produces arachidonic acid and lysophosphatidylcholine. These phospholipid-derived messengers, particularly diacylglycerol, activate PKC, thereby increasing the efficiency of free cytosolic Ca2+ concentration ([Ca2+]c) on exocytosis of insulin granules. IP3, also produced by PLC, causes a rapid elevation of [Ca2+]c by mobilizing Ca2+ from the endoplasmic reticulum; the resulting fall in Ca2+ in the organelle produces a small capacitative Ca2+ entry. ACh also depolarizes the plasma membrane of β-cells by a Na+- dependent mechanism. When the plasma membrane is already depolarized by secretagogues such as glucose, this additional depolarization induces a sustained increase in [Ca2+]c. Surprisingly, ACh can also inhibit voltage-dependent Ca2+ channels and stimulate Ca2+ efflux when [Ca2+]c is elevated. However, under physiological conditions, the net effect of ACh on [Ca2+]c is always positive. The insulinotropic effect of ACh results from two mechanisms: one involves a rise in [Ca2+]c and the other involves a marked, PKC-mediated increase in the efficiency of Ca2+ on exocytosis. The paper also discusses the mechanisms explaining the glucose dependence of the effects of ACh on insulin release.

Inhibition of Ca2+ transport pathways in thymic lymphocytes by econazole, miconazole, and SKF 96365

1993 ◽  
Vol 264 (3) ◽  
pp. C654-C662 ◽  
Author(s):  
M. J. Mason ◽  
B. Mayer ◽  
L. J. Hymel
Keyword(s):  
Plasma Membrane ◽  
Sarcoplasmic Reticulum ◽  
Divalent Cation ◽  
Selective Inhibitors ◽  
Transport Pathways ◽  
Cation Uptake ◽  
Inositol 1,4,5 Trisphosphate ◽  
Cytochrome P 450

Cytochrome P-450 has been proposed to underlie the mechanism of regulation of the plasma membrane Ca2+ permeability by the Ca2+ content of the inositol 1,4,5-trisphosphate-sensitive Ca2+ pool. We have investigated the effects on divalent cation uptake in rat thymic lymphocytes of three structurally related imidazole reagents reported to inhibit redox mechanisms. Changes in intracellular Ca2+ concentration and intracellular Mn2+ concentration were measured fluorimetrically with indo-1 and/or quin-2. Econazole, miconazole, and SKF 96365 were found to be potent blockers of Ca2+ and Mn2+ uptake activated by release of Ca2+ from intracellular stores induced by thapsigargin. Additionally, we found that concentrations of these agents required to abolish divalent cation uptake also released Ca2+ from the thapsigargin-sensitive intracellular stores, consistent with inhibition of the endosomal Ca(2+)-ATPase. In agreement with this suggestion, we have found that all three of these agents are potent inhibitors of isolated sarcoplasmic reticulum Ca(2+)-ATPase. We conclude that econazole, miconazole, and SKF 96365 inhibit cytochrome P-450-independent filling of intracellular Ca2+ pools, as well as store-regulated Ca2+ entry, and caution against the use of these compounds as selective inhibitors of cytochrome P-450.

scholarly journals Cytochrome P-450 may link intracellular Ca2+ stores with plasma membrane Ca2+ influx

1991 ◽  
Vol 274 (1) ◽  
pp. 193-197 ◽  
Author(s):  
J Alvarez ◽  
M Montero ◽  
J García-Sancho
Keyword(s):  
Plasma Membrane ◽  
Aryl Hydrocarbon Hydroxylase ◽  
Plasma Membrane Permeability ◽  
Aryl Hydrocarbon ◽  
Oxygen Scavenging ◽  
Aryl Hydrocarbon Hydroxylase Activity ◽  
Cytochrome P 450 ◽  
Degree Of Filling ◽  
Ca2 Channels ◽  
Dependent Mechanism

We have studied the mechanism of the regulation of plasma membrane Ca2+ permeability by the degree of filling of the intracellular Ca2+ stores. Using Mn2+ as a Ca2+ surrogate for plasma membrane Ca2+ channels, we found that Mn2+ uptake by rat thymocytes is inversely related to the degree of filling of the intracellular Ca2+ stores. This store-dependent plasma membrane permeability is inhibited by oxygen scavenging, CO, imidazole antimycotics and other cytochrome P-450 inhibitors. The pattern of inhibition is similar to that reported previously for the inhibition of microsomal cytochrome P-450-mediated aryl hydrocarbon hydroxylase activity of lymphocytes. Several calmodulin antagonists, both phenothiazinic (trifluoperazine, fluphenazine and chlorpromazine) and dibenzodiazepinic (clozapine), accelerate Mn2+ uptake by cells with Ca2(+)-filled stores, and this effect is prevented by imidazole antimycotics. Our results suggest that cytochrome P-450 may be the link between the stores and the plasma membrane Ca2+ pathway. We propose a model in which this cytochrome, sited at the stores, stimulates plasma membrane Ca2+ influx. This stimulatory effect is, in turn, prevented by the presence of Ca2+ inside the stores, possibly via a calmodulin-dependent mechanism.

scholarly journals Heparin binds with high affinity to voltage-dependent L-type Ca2+ channels. Evidence for an agonistic action.

1990 ◽  
Vol 265 (19) ◽  
pp. 11156-11166
Author(s):  
H G Knaus ◽  
F Scheffauer ◽  
C Romanin ◽  
H G Schindler ◽  
H Glossmann
Keyword(s):  
High Affinity ◽  
Voltage Dependent ◽  
Ca2 Channels

scholarly journals Control of Ca2+ entry into HL60 and U937 human leukaemia cells by the filling state of the intracellular Ca2+ stores

1993 ◽  
Vol 289 (3) ◽  
pp. 761-766 ◽  
Author(s):  
S R Alonso-Torre ◽  
J Alvarez ◽  
M Montero ◽  
A Sanchez ◽  
J García-Sancho
Keyword(s):  
Plasma Membrane ◽  
Inositol Phosphate ◽  
Platelet Activating Factor ◽  
Membrane Receptors ◽  
Plasma Membrane Permeability ◽  
Prolonged Incubation ◽  
Differentiated Cells ◽  
Cytochrome P 450 ◽  
Filling State ◽  
Ca2 Channels

Differentiation of HL60 cells by treatment with dimethyl sulphoxide induces the expression of membrane receptors for N-formylmethionyl-leucyl-phenylalanine (fMLP) and for platelet-activating factor (PAF). In these cells both agonists produced an increase in the cytosolic Ca2+ concentration ([Ca2+]i) by release of Ca2+ from the intracellular stores, followed shortly by an acceleration of the entry of Ca2+ or Mn2+, used here as a Ca2+ surrogate for Ca2+ channels. Cytochrome P-450 inhibitors blocked the agonist-induced entry of Ca2+ or Mn2+ with no modification of Ca2+ release from the stores. Emptying the intracellular Ca2+ stores either by treatments inducing no inositol phosphate production, such as prolonged incubation in Ca(2+)-free medium or treatment with the Ca2+ ionophore ionomycin, increased the plasma-membrane permeability to Ca2+ and Mn2+. This Ca(2+)-store-regulated Mn2+ entry was inhibited by Ni2+ and by cytochrome P-450 inhibitors. Refilling of the Ca2+ stores by incubation in Ca(2+)-containing medium restored low Mn2+ permeability. The same mechanism is present and functional in non-differentiated cells, before expression of membrane receptors for fMLP and PAF. These results suggest that agonist-induced Ca2+ (Mn2+) entry is secondary to the emptying of the intracellular Ca2+ stores, which in turn activates plasma-membrane channels by a mechanism involving cytochrome P-450.

Distribution of Ca2+ channels on cochlear outer hair cells revealed by fluorescent dihydropyridines

1996 ◽  
Vol 271 (3) ◽  
pp. C944-C949 ◽  
Author(s):  
T. Oshima ◽  
K. Ikeda ◽  
M. Furukawa ◽  
N. Ueda ◽  
H. Suzuki ◽  
...  
Keyword(s):  
Plasma Membrane ◽  
Hair Cells ◽  
Laser Scanning ◽  
Basolateral Membrane ◽  
Outer Hair Cells ◽  
Spatial Integration ◽  
Heterogeneous Distribution ◽  
Voltage Dependent ◽  
Basolateral Plasma Membrane ◽  
Ca2 Channels

Physiological evidence has shown that cochlear outer hair cells (OHC) possess L-type voltage-dependent Ca2+ channels through which Ca2+ enters the OHC during depolarization. Their subcellular distribution has, however, remained unclear. In this study, the distribution of L-type Ca2+ channels on the basolateral plasma membrane of OHC has been demonstrated by the use of a laser scanning confocal microscope (LSCM) and a fluorescent probe DMBODIPY-DHP. The fluorescent staining pattern on the basolateral wall is nonuniform, suggesting a heterogeneous distribution of the channels in the plasma membrane. Direct imaging of intracellular Ca2+ visualized in real time by means of the LSCM and the fluorescent Ca2+ probe fluo 3 revealed temporal and spatial integration of Ca2+ movements and Ca2+ channel distribution. Exposure to high-K+ solution induced heterogeneity in the subcellular increase in the intracellular Ca2+ concentration. These results suggest that the heterogeneous distribution of L-type Ca2+ channels on the basolateral membrane might induce heterogeneous intracellular Ca2+ distribution during electrical activity in the OHC.

scholarly journals Cytokinin stimulates dihydropyridine-sensitive calcium uptake in moss protoplasts

1993 ◽  
Vol 90 (23) ◽  
pp. 10937-10941 ◽  
Author(s):  
K S Schumaker ◽  
M J Gizinski
Keyword(s):  
Plasma Membrane ◽  
Gibberellic Acid ◽  
Calcium Uptake ◽  
Indoleacetic Acid ◽  
Early Event ◽  
Bud Formation ◽  
Voltage Dependent ◽  
Km Value ◽  
Ca2 Channels ◽  
Stimulation Of

Ca2+ influx through dihydropyridine (DHP)-sensitive Ca2+ channels is thought to be an early event in cytokinin-induced bud formation in moss protonema because DHP antagonists inhibit bud formation in the presence of cytokinin and DHP agonists stimulate bud formation in the absence of cytokinin [Conrad, P. A. & Helper, P. K. (1988) Plant Physiol. 86, 684-687]. In the present study, we established the presence of a DHP-sensitive Ca2+ transport system by measuring 45Ca2+ influx into moss protoplasts. Ca2+ influx was stimulated by external KCl (up to 5 mM), indicating that transport is voltage-dependent. K(+)-induced Ca2+ influx was DHP-sensitive with > 50% inhibition at 500 nM nifedipine. Ca2+ influx was stimulated by increasing concentrations of the DHP Ca2+ channel agonist Bay K8644 with half-maximal effects at 25 nM; this stimulation was seen only in the absence of K+, suggesting that the agonist works preferentially on polarized membranes. Ca2+ influx was also inhibited by phenylalkylamines (verapamil) and benzothiazepines (diltiazem). The phytohormone 6-benzylaminopurine consistently stimulated Ca2+ influx with a Km value of 1 nM, whereas adenine, indoleacetic acid, and gibberellic acid had no effect on Ca2+ transport. The cytokinins kinetin and trans-zeatin caused a greater stimulation of Ca2+ influx and induced more bud formation than did 6-benzylaminopurine. These results indicate that Ca2+ is taken up into moss protoplasts through voltage-dependent DHP-sensitive Ca2+ channels on the plasma membrane and that one of the cytokinin effects in the induction of bud formation is regulation of this plasma membrane Ca2+ channel.

scholarly journals Agonist-induced Ca2+ influx into human platelets is secondary to the emptying of intracellular Ca2+ stores

1991 ◽  
Vol 280 (3) ◽  
pp. 783-789 ◽  
Author(s):  
M T Alonso ◽  
J Alvarez ◽  
M Montero ◽  
A Sanchez ◽  
J García-Sancho
Keyword(s):  
Plasma Membrane ◽  
Platelet Activating Factor ◽  
Human Platelets ◽  
Temperature Dependent ◽  
Plasma Membrane Permeability ◽  
Low Concentrations ◽  
Cytochrome P 450 ◽  
Filling State ◽  
Ca2 Channels ◽  
Stimulation Of

We have studied the relation between the filling state of the intracellular Ca2+ stores and the plasma-membrane permeability to Mn2+, used here as a Ca2+ surrogate for Ca2+ channels. Emptying of the intracellular Ca2+ stores either by incubation in Ca(2+)-free medium or by treatment with low concentrations of the Ca2+ ionophore ionomycin accelerated the influx of Mn2+. Refilling of the Ca2+ stores by incubation in Ca(2+)-containing medium restores low Mn2+ permeability. This Ca(2+)-store-regulated permeability was inhibited by Ni2+ and by cytochrome P-450 inhibitors. Stimulation of platelets with thrombin produced Ca2+ release from the intracellular stores, which was followed, after a temperature-dependent lag (2 s at 37 degrees C; 5 s at 18 degrees C), by an acceleration of Mn2+ influx. Cytochrome P-450 inhibitors prevented the thrombin-induced Mn2+ influx, with little effect on the Ca2+ mobilization from the intracellular stores. Ki values were similar to those estimated for inhibition of the store-regulated permeability in non-stimulated platelets. Similar results were found in platelets stimulated by platelet-activating factor or by ADP. We propose that agonist-induced Ca2+ (Mn2+) influx in platelets is secondary to the emptying of the intracellular Ca2+ stores. The activation of the plasma-membrane Ca2+ (Mn2+) pathway may take place by a mechanism involving microsomal cytochrome P-450, similar to that described previously in thymocytes [Alvarez, Montero & García-Sancho (1991) Biochem. J. 274, 193-197] and neutrophils [Montero, Alvarez & García-Sancho (1991) Biochem. J. 277, 73-79].

scholarly journals Partition of the organochlorine insecticide lindane into the human sperm surface induces membrane depolarization and Ca2+ influx

1997 ◽  
Vol 321 (3) ◽  
pp. 691-698 ◽  
Author(s):  
Leopoldo SILVESTRONI ◽  
Roberto FIORINI ◽  
Simonetta PALLESCHI
Keyword(s):  
Plasma Membrane ◽  
Human Sperm ◽  
Membrane Depolarization ◽  
Organochlorine Insecticide ◽  
Dipole Potential ◽  
Membrane Dipole Potential ◽  
High K ◽  
Voltage Dependent ◽  
Sperm Plasma Membrane ◽  
Influx Pathways

The effects of the insecticide lindane (the γ-isomer of 1,2,3,4,5,6-hexachlorocyclohexane) on membrane potential, cytosolic free Ca2+ concentration ([Ca2+]i) and surface biophysical properties were studied in human spermatozoa. The insecticide induces rapid, transient and reproducible membrane depolarization and opening of voltage-dependent Ca2+ channels leading to an increase in [Ca2+]i. In contrast with the effect in somatic cells, lindane did not affect γ-aminobutyric acid receptor-linked Cl- currents. Ca2+ and K+ currents were found to drive lindane-induced membrane depolarization and repolarization respectively, whereas Na+ and Cl- fluxes appear not to have a role in the phenomenon. The insecticide was still able to produce membrane depolarization both in the combined absence of extracellular Ca2+ and Na+ and in high-K+ buffer, suggesting that lindane alters the membrane dipole potential. In agreement with this, Laurodan and Prodan fluorescence spectroscopy revealed that lindane partition into the sperm plasma membrane lowers water molecular dynamics in the uppermost region of the membrane external leaflet, probably as the result of reordering of water dipoles. We propose that the first effect of lindane partitioning into the sperm plasma membrane is a change in the membrane dipole potential, which results in the activation of membrane-located Ca2+-influx pathways.

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