scholarly journals Histamine and a guanine nucleotide increase calcium permeability in pig aortic microsomal fractions

1990 ◽  
Vol 267 (1) ◽  
pp. 105-109 ◽  
Author(s):  
L M Blayney ◽  
A C Newby
Keyword(s):  
Endoplasmic Reticulum ◽  
Steady State ◽  
Guanine Nucleotide ◽  
Intact Cells ◽  
Receptor Sites ◽  
H2 Antagonist ◽  
Dependent Inhibition ◽  
Calcium Permeability ◽  
H1 Antagonist ◽  
Stimulation Of

ATP-dependent Ca2+ accumulation was measured in pig aortic microsomal fractions containing plasmalemma and endoplasmic reticulum. In vesicles sonicated with histamine, to allow access to internally located receptor sites, guanosine 5′-[beta gamma-imido]triphosphate (p[NH]ppG), added to activate externally located guanine-nucleotide-transducing proteins, caused a concentration-dependent decrease in steady-state Ca2+ accumulation that was reversed by guanosine 5′-[beta-thio]diphosphate. In the presence of p[NH]ppG, sonication with histamine produced a concentration-dependent inhibition of Ca2+ accumulation that could be antagonized by the H1 antagonist mepyramine, but not by the H2 antagonist cimetidine. The inhibition of steady-state Ca2+ accumulation could have resulted from an inhibition of ATP-dependent Ca2+ uptake or a stimulation of Ca2+ release. We observed, however, that p[NH]ppG plus histamine stimulated, rather than inhibited, Ca2(+)-ATPase activity. We concluded that p[NH]ppG and histamine acted together to increase Ca2+ permeability. In support of this, p[NH]ppG accelerated efflux of Ca2+ from passively loaded vesicles sonicated with, but not without, histamine. The effect of p[NH]ppG was unlikely to be due to Ins(1,4,5)P3 (and hence release from endoplasmic-reticulum vesicles), since addition of Ins(1,4,5)P3 to vesicles sonicated with histamine did not alter steady-state Ca2+ accumulation. Our results therefore suggest that histamine and p[NH]ppG increased the permeability of the plasmalemma vesicles and may thus model the process of receptor-mediated Ca2+ entry into intact cells.

scholarly journals Inositol 1,4,5-trisphosphate mobilizes intracellular Ca2+ from permeabilized insulin-secreting cells

1984 ◽  
Vol 223 (2) ◽  
pp. 467-473 ◽  
Author(s):  
T J Biden ◽  
M Prentki ◽  
R F Irvine ◽  
M J Berridge ◽  
C B Wollheim
Keyword(s):  
Endoplasmic Reticulum ◽  
Steady State ◽  
Plasma Membranes ◽  
Cell Protein ◽  
Mitochondrial Activity ◽  
Rinm5f Cells ◽  
Cation Composition ◽  
Inositol 1,4,5 Trisphosphate ◽  
Insulin Secreting Cells ◽  
Stimulation Of

A possible role in secretory processes is proposed for inositol 1,4,5-triphosphate (IP3), based upon investigations of the Ca2+ steady state maintained by ‘leaky’, insulin-secreting RINm5F cells. These cells had been treated with digitonin to permeabilize their plasma membranes and thereby ensure that only intracellular Ca2+ buffering mechanisms were active. When placed in a medium with a cation composition resembling that of the cytosol, cells rapidly took up Ca2+ as measured by a Ca2+-specific minielectrode. Two Ca2+ steady states were observed. A lower level of around 120nM required ATP-dependent Ca2+ uptake and was probably determined by the endoplasmic reticulum. The higher steady state (approx. 800 nM), seen only in the absence of ATP, was shown to be due to mitochondrial activity. IP3 specifically released Ca2+ accumulated in the ATP-dependent pool, but not from mitochondria, since Ca2+ release was demonstrated in the presence of the respiratory poison antimycin. The IP3-induced Ca2+ release was rapid, with 50% of the response being seen within 15s. The apparent Km was 0.5 microM and maximal concentrations of IP3 (2.5 microM) produced a peak Ca2+ release of 10 nmol/mg of cell protein, which was followed by re-uptake. A full Ca2+ response was seen if sequential pulses of 2.5 microM-IP3 were added at 20 min intervals, although there was a slight (less than 20%) attenuation if the intervening period was decreased to 10 min. These observations could be related to the rate of IP3 degradation which, in this system, corresponded to a 25% loss of added 32P label within 2 min, and a 75% loss within 20 min. The results suggest that IP3 might act as a link between metabolic, cationic and secretory events during the stimulation of insulin release.

scholarly journals Vasoconstrictor agonists activate G-protein-dependent receptor-operated calcium channels in pig aortic microsomes

1992 ◽  
Vol 282 (1) ◽  
pp. 81-84 ◽  
Author(s):  
L M Blayney ◽  
P W Gapper ◽  
A C Newby
Keyword(s):  
Steady State ◽  
Angiotensin Ii ◽  
Calcium Channels ◽  
G Protein ◽  
G Proteins ◽  
Intact Cells ◽  
Vasoconstrictor Agents ◽  
Receptor Sites ◽  
Alpha Beta ◽  
Ca2 Channels

Receptor-operated Ca2+ channels were characterized by their ability to decrease steady-state ATP-dependent Ca2+ accumulation into pig aortic microsomes. The vasoconstrictor agents noradrenaline, angiotensin II and adenosine 5′-[alpha beta-methylene]triphosphate (pp[CH2]pA) all decreased Ca2+ accumulation only when sonicated into vesicles (to allow access to receptor sites) and in the presence of guanosine 5′-[beta gamma-imido]triphosphate to activate transducing G-proteins. The effect of noradrenaline was inhibited by the alpha 2 antagonist yohimbine, but not by the alpha 1 antagonist prazosin. The effect of none of the agonists was reversed by diltiazem. SK&F 96365 (an inhibitor of receptor-mediated Ca2+ influx into intact cells) reversed the effect of noradrenaline, but not that of pp[CH2]pA, which suggests that at least two receptor-operated channels may be present in this preparation.

Activation of Hageman Factor by α-Adrenergic Stimulation

1970 ◽  
Vol 23 (03) ◽  
pp. 417-422 ◽  
Author(s):  
D. G McKay ◽  
J.-G Latour ◽  
Mary H. Parrish
Keyword(s):  
Disseminated Intravascular Coagulation ◽  
Adrenergic Receptor ◽  
Adrenergic Stimulation ◽  
Hageman Factor ◽  
Intravascular Coagulation ◽  
Receptor Sites ◽  
High Doses ◽  
Stimulation Of

SummaryThe infusion of epinephrine in high doses produces disseminated intravascular coagulation by activation of Hageman factor. The effect is blocked by phenoxybenz-amine and is therefore due to stimulation of α-adrenergic receptor sites.

Acidification of rat liver lysosomes: quantitation and comparison with endosomes

1993 ◽  
Vol 265 (4) ◽  
pp. C901-C917 ◽  
Author(s):  
R. W. Van Dyke
Keyword(s):  
Steady State ◽  
Membrane Potential ◽  
Rat Liver ◽  
Proton Pumps ◽  
Intact Cells ◽  
Early Endosomes ◽  
Medium Permeability ◽  
Electrogenic Proton Pump ◽  
Secondary Lysosomes ◽  
Permeability Studies

Both lysosomes and endosomes are acidified by an electrogenic proton pump, although studies in intact cells indicate that the steady-state internal pH (pHi) of lysosomes is more acid than that of endosomes. We undertook the present study to examine in detail the acidification mechanism of purified rat liver secondary lysosomes and to compare it with that of a population of early endosomes. Both endosomes and lysosomes exhibited ATP-dependent acidification, but proton influx rates were 2.4- to 2.7-fold greater for endosomes than for lysosomes because of differences in both buffering capacity and acidification rates, suggesting that endosomes exhibited greater numbers or rates of proton pumps. Lysosomes, however, exhibited a more acidic steady-state pHi due in part to a slower proton leak rate. Changes in medium Cl- increased acidification rates of endosomes more than lysosomes, and the lysosome ATP-dependent interior-positive membrane potential was only partially eliminated by high-Cl- medium. Permeability studies suggested that lysosomes were less permeable to Na+, Li+, and Cl- and more permeable to K+ and PO4(2-) than endosomes. Na-K-adenosine-triphosphatase did not appear to regulate acidification of either vesicle type. Endosome and lysosome acidification displayed similar inhibition profiles to N-ethylmaleimide, dicyclohexyl-carbodiimide, and vanadate, although lysosomes were somewhat more sensitive [concentration producing 50% maximal inhibition (IC50) 1 nM] to bafilomycin A1 than endosomes (IC50 7.6 nM). Oligomycin (1.5-3 microM) stimulated lysosome acidification due to shunting of membrane potential. Overall, acidification of endosomes and lysosomes was qualitatively similar but quantitatively somewhat different, possibly related to differences in the density or rate of proton pumps as well as vesicle permeability to protons, anions, and other cations.

scholarly journals Receptor-operated Ca2+ channels in gastric parietal cells: gastrin and carbachol induce Ca2+ influx in depleting intracellular Ca2+ stores

1993 ◽  
Vol 289 (1) ◽  
pp. 117-124 ◽  
Author(s):  
S Roche ◽  
J P Bali ◽  
R Magous
Keyword(s):  
Steady State ◽  
Receptor Activation ◽  
Parietal Cells ◽  
The Other ◽  
Bivalent Cation ◽  
Gtp Binding ◽  
Gastric Parietal Cells ◽  
Type Receptor ◽  
Ca2 Channels ◽  
Stimulation Of

The mechanism whereby gastrin-type receptor and muscarinic M3-type receptor regulate free intracellular Ca2+ concentration ([Ca2+]i) was studied in rabbit gastric parietal cells stimulated by either gastrin or carbachol. Both agonists induced a biphasic [Ca2+]i response: a transient [Ca2+]i rise, followed by a sustained steady state depending on extracellular Ca2+. Gastrin and carbachol also caused a rapid and transient increase in Mn2+ influx (a tracer for bivalent-cation entry). Pre-stimulation of cells with one agonist drastically decreased both [Ca2+]i increase and Mn2+ influx induced by the other. Neither diltiazem nor pertussistoxin treatment had any effect on agonist-stimulated Mn2+ entry. Thapsigargin, a Ca(2+)-pump inhibitor, induced a biphasic [Ca2+]i increase, and enhanced the rate of Mn2+ entry. Preincubation of cells with thapsigargin inhibits the [Ca2+]i increase as well as Mn2+ entry stimulated by gastrin or by carbachol. Thapsigargin induced a weak but significant increase in Ins(1,4,5)P3 content, but this agent had no effect on the agonist-evoked Ins(1,4,5)P3 response. In permeabilized parietal cells, Ins(1,4,5)P3 and caffeine caused an immediate Ca2+ release from intracellular pools, followed by a reloading of Ca2+ pools which can be prevented in the presence of thapsigargin. We conclude that (i) gastrin and carbachol mobilize common Ca2+ intracellular stores, (ii) Ca2+ permeability secondary to receptor activation involves neither a voltage-sensitive Ca2+ channel nor a GTP-binding protein from the G1 family, and (iii) agonists regulate common Ca2+ channels in depleting intracellular Ca2+ stores.

scholarly journals Human Homologs of the Putative G Protein-Coupled Membrane Progestin Receptors (mPRα, β, and γ) Localize to the Endoplasmic Reticulum and Are Not Activated by Progesterone

2006 ◽  
Vol 20 (12) ◽  
pp. 3146-3164 ◽  
Author(s):  
Tom Krietsch ◽  
Maria Sofia Fernandes ◽  
Jukka Kero ◽  
Ralf Lösel ◽  
Maria Heyens ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
G Protein ◽  
Cell Lines ◽  
Spotted Seatrout ◽  
Membrane Receptors ◽  
Takifugu Rubripes ◽  
Camp Production ◽  
Intact Cells ◽  
Progestin Receptors ◽  
G Protein Coupled

Abstract The steroid hormone progesterone exerts pleiotrophic functions in many cell types. Although progesterone controls transcriptional activation through binding to its nuclear receptors, it also initiates rapid nongenomic signaling events. Recently, three putative membrane progestin receptors (mPRα, β, and γ) with structural similarity to G protein-coupled receptors have been identified. These mPR isoforms are expressed in a tissue-specific manner and belong to the larger, highly conserved family of progestin and adiponectin receptors found in plants, eubacteria, and eukaryotes. The fish mPRα has been reported to mediate progesterone-dependent MAPK activation and inhibition of cAMP production through coupling to an inhibitory G protein. To functionally characterize the human homologs, we established human embryonic kidney 293 and MDA-MB-231 cell lines that stably express human mPRα, β, or γ. For comparison, we also established cell lines expressing the mPRα cloned from the spotted seatrout (Cynoscion nebulosus) and Japanese pufferfish (Takifugu rubripes). Surprisingly, we found no evidence that human or fish mPRs regulate cAMP production or MAPK (ERK1/2 or p38) activation upon progesterone stimulation. Furthermore, the mPRs did not couple to a highly promiscuous G protein subunit, Gαq5i, in transfection studies or provoke Ca2+ mobilization in response to progesterone. Finally, we demonstrate that transfected mPRs, as well as endogenous human mPRα, localize to the endoplasmic reticulum, and that their expression does not lead to increased progestin binding either in membrane preparations or in intact cells. Our results therefore do not support the concept that mPRs are plasma membrane receptors involved in transducing nongenomic progesterone actions.

Effects of cations on binding of human choriogonadotropin

1988 ◽  
Vol 66 (12) ◽  
pp. 1258-1264
Author(s):  
Patrick J. McIlroy
Keyword(s):  
Binding Sites ◽  
Regulatory Protein ◽  
Guanine Nucleotides ◽  
Guanine Nucleotide ◽  
Human Choriogonadotropin ◽  
Receptor Sites ◽  
Number Of Binding Sites ◽  
Receptor Number ◽  
Guanine Nucleotide Regulatory Protein ◽  
Low Ionic Strength

The effect of various salts on the binding of human choriogonadotropin to rat luteal membranes has been examined. Increasing salt concentrations had biphasic effects, initially increasing binding, then decreasing it. With NaCl, these effects were on both the affinity and the number of receptor sites. The affinity increased with increasing NaCl concentrations, to a maximum at 40 mM, and then decreased. Above 40 mM NaCl, the number of binding sites increased. NaCl also altered the effects of Mg2+ and guanyl nucleotides. At low ionic strength, Mg2+ was necessary to observe binding. Guanine nucleotides modulated this binding by decreasing the affinity. At 40 mM NaCl, Mg2+ increased receptor number without altering affinity. Guanyl nucleotides modulated this binding by reducing the number of sites to that observed in the absence of Mg2+. At 150 mM NaCl, Mg2+ and guanine nucleotides had no effect. The results suggest the presence of two pools of human choriogonadotropin receptor in rat corpus luteum, one coupled to the guanine nucleotide regulatory protein (Ns) and being Mg2+ dependent and guanine nucleotide sensitive, and the other not coupled to Ns and being Mg2+ independent and guanine nucleotide insensitive.

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