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1.
Teruyuki Yanagisawa Toshio Yamagishi Yuji Okada 《Cardiovascular drugs and therapy / sponsored by the International Society of Cardiovascular Pharmacotherapy》1993,7(Z3):565-574
The vasodilating mechanisms of the K+ channel openers—cromakalim, pinacidil, nicorandil, KRN2391, and Ki4032—were examined by measurement of the cytoplasmic Ca2+ concentration ([Ca2+]i) using the fura-2 method in canine or porcine coronary arterial smooth muscle. The five K+ channel openers all produced a reduction of [Ca2+]i in 5 and 30 mM KCl physiological salt solution (PSS), the effects of which were antagonized by tetrabutylammonium (TBA) or glibenclamide, but failed to affect [Ca2+]i in 45 and 90 mM MCl-PSS. Cromakalim and Ki4032 only partially inhibited the 30 mM KCl-induced contractures, whereas pinacidil, nicorandil, and KRN2391 nearly abolished contractions produced by high KCl-PSS. The increased [Ca2+]i and force produced by a thromboxane A2 analogue, U46619, were inhibited by K+ channel openers and verapamil. In the absence of extracellular Ca2+, U46619 induced a transient increase in [Ca2+]i with a contraction, which is effectively inhibited by cromakalim and Ki4032. Their inhibitory effects were blocked by TBA and counteracted by 20 mM KCl-induced depolarization. Cromakalim and Ki4032 did not affect caffeine-induced Ca2+ release. Cromakalim reduced U46619-induced IP3 production and TBA blocked this inhibitory effect. Thus, cromakalim and Ki4032 are more specific K+ channel openers than pinacidil, nicorandil, and KRN2391. The vasodilation related with a reduction of [Ca2+]i produced by K+ channel openers is due to the hyperpolarization of the plasma membrane resulting in not only the closure of voltage-dependent Ca2+ channels but also inhibition of the production of IP3 and Ca2+ release from intracellular stores related to stimulation of the thromboxane A2 receptor. 相似文献
2.
The cytoplasmic Ca2+ concentration ([Ca2+]i) was measured with dual wavelength fluorometry in glucagon-producing mouse pancreatic α-cells loaded with the indicator fura-2.
Spontaneous rhythmic activity in terms of slow oscillations from a basal level was observed at 3 mM glucose. Like in the insulin-secreting β-cells the generation of [Ca2+]i oscillations in the α-cells was affected by the activity of the Na/K pump. Blocking the pump with ouabain resulted in an
initial rise of [Ca2+]i followed by gradual return to the basal level. The oscillations were transformed into sustained elevation of [Ca2+]i by 10 mM
l-glycine, which is cotransported with Na+. A similar but less pronounced effect was obtained when Na+ was cotransported with 10 mM of the nonmetabolizable amino acid α-amino-isobutyric acid.l-glycine induced sustained increase of [Ca2+]i also when the oscillatory activity was suppressed by exposing the α-cells to 20 mM glucose in the presence of insulin. The observation that carbachol induces a [Ca2+]i response in isolated α-cells calls for reconsideration of current ideas that muscarinic stimulation of glucagon release is
an indirect effect mediated by adjacent β-cells. 相似文献
3.
This article describes studies on the glucose-induced responses of intracellular Ca2+ concentration ([Ca2+]i), insulin release, and redistribution of calbindin-D28k, a calcium-binding regulatory protein, in β-cells of pancreatic islets of calbindin-D28k knockout (KO) and wild-type mice (C57BL6) as well as in βHC-13 control cells and βHC-13 CaBP40 cells (β-cell line overexpressing
calbindin-D28k). Upon increasing the glucose concentration from 2.8 to 30 mM, islets of KO mice showed a significantly greater increase in [Ca2+]i (mean increase in [Ca2+]i, i.e., Δ[Ca2+], was 296 nM) compared with wild-type mice (Δ[Ca2+]i=97 nM). βHC-13 CaBP40 cells showed little change in [Ca2+]i upon elevation of glucose from 5.5 to 32.7 mM, whereas βHC-13 control cells exhibited significant increases in [Ca2+]i (Δ[Ca2+]i=510 nM). Similarly, upon addition of 30 mM glucose, the rate of insulin release increased from 25.2 (basal rate) to 145.2 pg/mL/min in βHC-13 control cells, whereas
in βHC-13 CaBP40 cells the rate of insulin release was only 27.5 pg/mL/min in high glucose. Thus, levels of calbindin-D28k in β-cells affect both [Ca2+]i and insulin secretion in response to glucose. The three-dimensional reconstruct of confocal immunofluorescent images showed
that glucose caused redistribution of calbindin-D28k resulting in co-localization in the region of L-type voltage-dependent calcium channels (VDCC). This colocalization may be
an important regulatory function concerning Ca2+ influx via L-type VDCC and exocytosis of insulin granules. 相似文献
4.
The effects of gonadotropin-releasing hormone (GnRH) and GnRH-associated peptide (GAP) on cytosolic free calcium concentration
([Ca2+]i) were investigated in 20 human nonfunctioning pituitary adenomas. We divided these tumors into three classes according to
their response pattern to hypothalamic peptides. In type I adenomas (8 out of 20 adenomas), GnRH and GAP mobilized intracellular
calcium ions stored in a thapsigargin (TG)-sensitive store. For the same concentration of agonist, two distinct patterns of
GnRH-GAP-induced Ca2+ mobilization were observed (1) sinusoidal oscillations, and (2) monophasic transient. The latter is followed by a protein
kinase C (PKC)-dependent increase in calcium influx through L-type channels. In type II adenomas (7 out of 20 adenomas), GnRH
and GAP only stimulate calcium influx through dihydropyridine-sensitive Ca2+ channels by a PKC-dependent mechanism. TG (1 μM) did not affect [Ca2+]i in these cells, suggesting that they do not possess TG-sensitive Ca2+ pools. All the effects of GnRH and GAP were blocked by an inhibitor of phospholipase C (PLC), suggesting that they were owing
to the activation of the phosphoinositide turnover. Type I and type II adenoma cells showed spontaneous Ca2+ oscillations that were blocked by dihydropyridines and inhibition of PKC activity. GnRH and GAP had no effect on the [Ca2+]i of type III adenoma cells that were also characterized by a low resting [Ca2+]i and by the absence of spontaneous Ca2+ fluctuations. K+-induced depolarization provoked a reduced Ca2+ influx, whereas TG had no effect on the [Ca2+]i of type III adenoma cells. The variety of [Ca2+]i response patterns makes these cells a good cell model for studying calcium homeostasis in pituitary cells. 相似文献
5.
The present study was conducted to investigate the effects of the diabetic condition on the Ca2+ mobilization and glutamate release in cerebral nerve terminals (synaptosomes). Diabetes was induced in male mice by intraperitoneal injection of streptozotocin. Cytosolic free Ca2+ concentration ([Ca2+]i) and glutamate release in synaptosomes were determined using fura-2 and enzyme-linked fluorometric assay, respectively. Diabetes significantly enhanced the ability of the depolarizing agents K+ and 4-aminopyridine (4-AP) to increase [Ca2+]i. In addition, diabetes significantly enhanced K+- and 4-AP-evoked Ca2+-dependent glutamate release. The pretreatment of synaptosomes with a combination of ω-agatoxin IVA (a P-type Ca2+ channel blocker) and ω-conotoxin GVIA (an N-type Ca2+ channel blocker) inhibited K+- or 4-AP-induced increases in [Ca2+]i and Ca2+-dependent glutamate release in synaptosomes from the control and diabetic mice to a similar extent, respectively. These results indicate that diabetes enhances a K+- or 4-AP-evoked Ca2+-dependent glutamate release by increasing [Ca2+]i via stimulation of Ca2+ entry through both P- and N-type Ca2+ channels. 相似文献
6.
This study was undertaken to investigate the relationship between dopamine (DA) induced changes in the cytosolic calcium concentration
([Ca2+]i) and the rate of prolactin secretion using GH4ZR7, a rat pituitary cell line, which express only one subtype of D2 receptor. GH4ZR7 cells were loaded with Fluo-3, a fluorescent Ca2+ indicator, and then perifused with two different doses of DA (10−7 mol/L and 5×10−4 mol/L). We monitored changes in [Ca2+]i and rate of prolactin release simultaneously by attaching a spectrofluorometer to a dynamic perifusion system. DA has stimulatory
and inhibitory effect on prolactin secretion in GH4ZR7 cells; 10−7 mol/L DA slightly increased [Ca2+]i and stimulated prolactin release, whereas 5×10−4 mol/L DA decreased [Ca2+]i and inhibited prolactin secretion. When the cells were pretreated with pertussis toxin (PTX), 10−7 mol/L DA had no significant change in [Ca2+]i while stimulating prolactin release, and 5×10−4 mol/L DA reduced [Ca2+]i without having any significant effect on the rate of prolactin secretion. The results of this study demonstrate that changes
in [Ca2+]i do not always correlate with the rate of prolactin release from lactotrophs. The dissociation between [Ca2+]i and prolactin release is somewhat expected considering the diverse role of [Ca2+]i and post-[Ca2+]i events, which can change the rate of prolactin release. 相似文献
7.
Summary In rat cardiac myocytes, calcium efflux by Na+/Ca2+-exchange is expected only during ventricular systole following initial action potential repolarization. In contrast, in guinea-pigs, calcium influx via Na+/Ca2+-exchange is expected only during the initial portion of the action potential. Thus electrical stimulation is expected to result in reduced intracellular calcium ([Ca2+]i) in rat and an increase in guinea pig. We tested this hypothesis by measuring total cellular calcium ([Ca]tot) using45Ca following stimulation of isolated rat and guinea-pig ventricular myocytes. Many studies have also emphasized that the rate and the direction of Na+/Ca2+-exchange across the sarcolemma are in part dependent on the magnitude of the transsarcolemmal sodium gradient. Thus, increasing intracellular sodium ([Na+]i) is expected to result in an increased [Ca2+]i. This hypothesis was also tested by measuring [Ca]tot following veratrine administration. Enzymatically isolated rat and guinea-pig ventricular myocytes were divided into two groups; non-stimulated and stimulated (1 Hz). The concentration-dependent effects of veratrine (1,10,100 g/ml) on [Ca]tot were determined in both these groups. In the absence of veratrine, non-stimulated rat myocytes had a significantly higher [Ca]tot than did stimulated ones. Non-stimulated guinea-pig myocytes had a significantly lower [Ca]tot when compared with stimulated ones Veratrine increased [Ca]tot in both species in a concentration-dependent fashion. In addition, following veratrine the difference between [Ca]tot in non-stimulated and stimulated rat myocytes was no longer significant. These results support those of others who have demonstrated that stimulation is associated with a gain of cellular calcium in both rabbit and guinea-pig ventricle and a calcium loss in rat ventricle. In addition, the increase in [Ca]tot following veratrine was similar to the results of others that have shown an increase in [Ca2+]i following exposure to veratrum alkaloids. Thus, we have demonstrated, using a technique limited to determination of [Ca]tot, that this parameter may reflect changes produced by alteration of Na+/Ca2+-exchange. 相似文献
8.
H. Kindmark M. Köhler P. Arkhammar S. Efendic O. Larsson S. Linder T. Nilsson Dr. P. O. Berggren 《Diabetologia》1994,37(11):1121-1131
Summary Plasma insulin levels in healthy subjects oscillate and non-insulin-dependent diabetic patients display an irregular pattern of such oscillations. Since an increase in cytoplasmic free Ca2+ concentration ([Ca2+]i) in the pancreatic beta cell is the major stimulus for insulin release, this study was undertaken to investigate the dynamics of electrical activity, [Ca2+]i-changes and insulin release, in stimulated islets from subjects of varying glucose tolerance. In four patients it was possible to investigate more than one of these three parameters. Stimulation of pancreatic islets with glucose and tolbutamide sometimes resulted in the appearance of oscillations in [Ca2+]i, lasting 2–3 min. Such oscillations were observed even in some islets from patients with impaired glucose tolerance. In one islet from a diabetic patient there was no response to glucose, whereas that islet displayed [Ca2+]i-oscillations in response to tolbutamide, suggesting that sulphonylurea treatment can mimic the complex pattern of glucose-induced [Ca2+]i-oscillations. We also, for the first time, made patch-clamp recordings of membrane currents in beta-cells in situ in the islet. Stimulation with glucose and tolbutamide resulted in depolarization and appearance of action potentials. The islet preparations responded to stimulation with a number of different secretagogues with release of insulin. The present study shows that human islets can respond to stimulation with glucose and sulphonylurea with oscillations in [Ca2+]i, which is the signal probably underlying the oscillations in plasma insulin levels observed in healthy subjects. Interestingly, even subjects with impaired glucose tolerance had islets that responded with oscillations in [Ca2+]i upon glucose stimulation, although it is not known to what extent the response of these islets was representative of most islets in these patients.Abbreviations [Ca2+]i
Cytoplasmic free Ca2+
- NIDDM
non-insulin-dependent diabetes mellitus
- DMSO
dimethylsulphoxide
- PC
pancreatic cancer 相似文献
9.
Fenghua Li Kazuro Sugishita Zhi Su Issaku Ueda William H. Barry 《Journal of molecular and cellular cardiology》2001,33(12):2145
ATP depletion due to ischemia or metabolic inhibition (MI) causes Na+and Ca2+accumulation in myocytes, which may be in part due to opening of connexin-43 hemichannels. Halothane (H) has been shown to reduce conductance of connexin-43 hemichannels and to protect the heart against ischemic injury. We therefore investigated the effect of halothane on [Ca2+]iand [Na+]iin myocytes during MI. Isolated rabbit left ventricular myocytes were loaded with 4μ m fluo-3 AM for 30 min, or with 5 μ m sodium green AM for 60 min at 37°C. After washing, the myocytes were exposed to: (1) Normal HEPES solution; (2) MI solution (2 m
NaCN, 20 m
2-deoxy-
-glucose and 0-glucose); or (3) MI+H (0.95 m
, 4.7 m
) for 60 min. Propidium iodide (PI, 25 μ m) was added to all samples before data acquisition. The fluorescence intensity was measured by flow cytometry with 488 nm excitation and 530 nm emission for fluo-3 or sodium green, and 670 nm for PI. The [Ca2+]iand [Na+]iwere then calculated by calibration. In some experiments, the effect of 10 μ m tetrodotoxin (TTX) and 20 μ m nifedipine (NIF) were studied. Metabolic inhibition for 60 min caused a significant increase in [Ca2+]iand [Na+]iin myocytes when compared to controls, which was significantly reduced by halothane in a dose-dependent fashion. In the presence of TTX and NIF, halothane also significantly reduced the rise in the [Ca2+]iand [Na+]iin myocytes subjected to MI. 1-heptanol, another gap junction blocker, had similar effects. Thus, halothane reduced [Ca2+]iand [Na+]ioverload produced by MI in myocytes. This effect is not solely due to block of voltage-gated Na+and Ca2+channels, and is likely mediated by inhibiting the opening of connexin-43 hemichannels. 相似文献
10.
Aims/hypothesis Islets or beta cells from Sur1–/– mice were used to determine whether changes in plasma membrane potential (Vm) remain coupled to changes in cytosolic Ca2+ ([Ca2+]i) in the absence of KATP channels and thus provide a triggering signal for insulin secretion. The study also sought to elucidate whether [Ca2+]i influences oscillations in Vm in sur1–/– beta cells.Methods Plasma membrane potential and ion currents were measured with microelectrodes and the patch–clamp technique. [Ca2+]i was monitored with the fluorescent dye fura-2. Insulin secretion from isolated islets was determined by static incubations.Results Membrane depolarisation of Sur1–/– islets by arginine or increased extracellular K+, elevated [Ca2+]i and augmented insulin secretion. Oligomycin completely abolished glucose-stimulated insulin release from Sur1–/– islets. Oscillations in Vm were influenced by [Ca2+]i as follows: (1) elevation of extracellular Ca2+ lengthened phases of membrane hyperpolarisation; (2) simulating a burst of action potentials induced a Ca2+-dependent outward current that was augmented by increased Ca2+ influx through L-type Ca2+ channels; (3) Ca2+ depletion of intracellular stores by cyclopiazonic acid increased the burst frequency in Sur1–/– islets, elevating [Ca2+]i and insulin secretion; (4) store depletion activated a Ca2+ influx that was not inhibitable by the L-type Ca2+ channel blocker D600.Conclusions/interpretation Although Vm is largely uncoupled from glucose metabolism in the absence of KATP channels, increased electrical activity leads to elevations of [Ca2+]i that are sufficient to stimulate insulin secretion. In Sur1–/– beta cells, [Ca2+]i exerts feedback mechanisms on Vm by activating a hyperpolarising outward current and by depolarising Vm via store-operated ion channels. 相似文献
11.
Changes in ionic composition of airway surface fluid may modulate airway epithelial functions. We tested the hypothesis that
fluctuations of ambient ionic composition could affect airway epithelial Ca2+ dynamics and Ca2+-dependent cellular functions, including NO release and PGE2 production in vitro. The responses of intracellular Ca2+ concentration ([Ca2+]i) to changes in extracellular Cl− and Na+ concentrations ([Cl−]e, [Na+]e) in the human bronchial epithelial cell line, 16HBE cells, were measured by the fura-2 method. The NO release to the medium
after lowering [Cl−]e was measured by an amperometric NO sensor. PGE2 production was measured by radioimmunoassay. Changing to isotonic low [Cl−]e solution by substitution with gluconate caused a sustained increase in [Ca2+]i in a concentration-dependent manner, with the maximal [Ca2+]i increase from the baseline level being 243 ± 110 nM with Cl-free solution. The effect was not altered by thapsigargin but
abolished by EGTA and by Cl channel blockers, including diphenylamine-2-carboxylate, disodium 4,4′-diisothiocyanatostilbene-2,2′-disulfonate,
and disodium cromoglycate. In contrast, the effect of reduction of [Na+]e by substitution with N-methyl-D-glucamine+ on [Ca2+]i was less than that of reduction of [Cl−]e. The reduction of [Cl−]e caused a concentration-dependent rise in NO contents in the medium and PGE2 production. This release of NO was inhibited by EGTA but not by dexamethasone pretreatment. These results suggest that the
decrease in ambient [Cl−] induces Ca2+ mobilization probably through Ca2+ influx, followed by the release of NO and PGE2, thereby modulating various cellular functions. 相似文献
12.
Previous studies have shown that nitric oxide (NO) inhibits histamine-induced gastric acid secretion in isolated human gastric
glands. NO synthase has been found to be present in the human oxyntic mucosa and has been suggested to serve as a paracrine
regulator of gastric acid secretion. Histamine stimulation of parietal cells induces cytoskeletal rearrangements, recruitment
of H+/K+-ATPase-rich tubulovesicles to the apical membrane and expansion of intracellular canaliculi. The aim of the present study
was thus to investigate (i) the effect of an NO donor on histamine-induced cytological transformations and (ii) the influence
of increased [Ca2+]i on NO-induced morphological changes in human parietal cells. Human gastric glands were isolated and subjected to the NO donor
SNAP prior to histamine administration. [Ca2+]i was increased by photolysis of the caged Ca2+ compound NP-EGTA. The distribution of F-actin, ezrin, and H+/K+-ATPase was assessed by confocal microscopy. Ultrastructural analysis was performed using transmission electron microscopy.
SNAP did not influence the histamine-induced translocation of F-actin, ezrin, and H+/K+-ATPase but prevented an increase in the canalicular size. Elevation of [Ca2+]i in resting cells was found to mimic histamine-induced intraparietal cell transformations; however, NO-induced parietal cell
morphology was unaffected by a rise in [Ca2+]i. These results indicate that NO inhibits secretion of fluid into the canalicular lumen without affecting membrane recruitment
and that this effect is Ca2+-insensitive. 相似文献
13.
Summary A model of vascular endothelial cell is proposed to describe the mechanisms by which cytosolic calcium (Cai) is modulated and endothelium-derived relaxing factor (EDRF) and prostacyclin (PGI2) are released when the cell is stimulated by agonist. The intracellular Ca2+ store of the model cell is comprised of a superficial (sc) and a deep (dc) compartment. The dc Ca2+ content is refilled by the sc whose [Ca2+] is the same as extracellular Ca2+. Inositol (1,4,5)-trisphosphate (IP3) produced by agonist modifies the dc permeability which discharges its Ca2+ to the cytosol. The increase of Cai induces Ca2+ released from the sc. Ca2+-activated K+ current hyperpolarises the cell. The raised Cai releases PGI2 in the presence of IP3 while EDRF is released by Cai. The model explains satisfactorily the Ca2+ transient and autacoids production of the aortie endothelial cell without the need of calcium influx from extracellular space. The cytoplasmic Ca2+ oscillations observed in human endothelial cell from umbilical veins were reproduced by the model. Production of EDRF by the artery due to increase in pressre also simulated. 相似文献
14.
Eleonora Grandi Francesco S. Pasqualini Cristiana Corsi Stefano Severi 《Journal of molecular and cellular cardiology》2009,46(3):332-616
Reduction in [Ca2+]o prolongs the AP in ventricular cardiomyocytes and the QTc interval in patients. Although this phenomenon is relevant to arrhythmogenesis in the clinical setting, its mechanisms are counterintuitive and incompletely understood. To evaluate in silico the mechanisms of APD modulation by [Ca2+]o in human cardiomyocytes. We implemented the Ten Tusscher-Noble-Noble-Panfilov model of the human ventricular myocyte and modified the formulations of the rapidly and slowly activating delayed rectifier K+ currents (IKr and IKs) and L-type Ca2+ current (ICaL) to incorporate their known sensitivity to intra- or extracellular Ca2+. Simulations were run with the original and modified models at variable [Ca2+]o in the clinically relevant 1 to 3 mM range. The original model responds with APD shortening to decrease in [Ca2+]o, i.e. opposite to the experimental observations. Incorporation of Ca2+ dependency of K+ currents cannot reproduce the inverse relation between APD and [Ca2+]o. Only when ICaL inactivation process was modified, by enhancing its dependency on Ca2+, simulations predict APD prolongation at lower [Ca2+]o. Although Ca2+-dependent ICaL inactivation is the primary mechanism, secondary changes in electrogenic Ca2+ transport (by Na+/Ca2+ exchanger and plasmalemmal Ca2+-ATPase) contribute to the reversal of APD dependency on [Ca2+]o. This theoretical investigation points to Ca2+-dependent inactivation of ICaL as a mechanism primarily responsible for the dependency of APD on [Ca2+]o. The modifications implemented here make the model more suitable to analyze repolarization mechanisms when Ca2+ levels are altered. 相似文献
15.
Aims/hypothesis Chronic exposure to high concentrations of glucose has consistently been demonstrated to impair endothelium-dependent, nitric oxide (NO)-mediated vasodilation. In contrast, several clinical investigations have reported that acute exposure to high glucose, alone or in combination with insulin, triggers vasodilation. The aim of this study was to examine whether elevated glucose itself stimulates endothelial NO formation or enhances insulin-mediated endothelial NO release.Methods We measured NO release and vessel tone ex vivo in porcine coronary conduit arteries (PCAs). Intracellular Ca2+ was monitored in porcine aortic endothelial cells (PAECs) by fura-2 fluorescence. Expression of the Na+/glucose cotransporter-1 (SGLT-1) was assayed in PAECs and PCA endothelium by RT-PCR.Results Stimulation of PCAs with d-glucose, but not the osmotic control l-glucose, induced a transient increase in NO release (EC5010 mmol/l), mediated by a rise in intracellular Ca2+ levels due to an influx from the extracellular space. This effect was abolished by inhibitors of the plasmalemmal Na+/Ca2+ exchanger (dichlorobenzamil) and the SGLT-1 (phlorizin), which was found to be expressed in aortic and coronary endothelium. Alone, d-glucose did not relax PCA, but did augment the effect of insulin on NO release and vasodilation.Conclusions/interpretation An increased supply of extracellular d-glucose appears to enhance the activity of the endothelial isoform of nitric oxide synthase by increasing intracellular Na+ concentrations via SGLT-1, which in turn stimulates an extracellular Ca2+ influx through the Na+/Ca2+ exchanger. This mechanism may be responsible for glucose-enhanced, insulin-dependent increases in tissue perfusion (including coronary blood-flow), thus accelerating glucose extraction from the blood circulation to limit the adverse vascular effects of prolonged hyperglycaemia. 相似文献
16.
We have investigated the influence of the intracellular free radical donors hydroxylamine (giving nitric oxide [NO]) and tert-butylhydroperoxide (giving hydroperoxide [“H2O2”]) on glucose- and cyclic adenosine monophosphate (cAMP)-induced transduction signaling in islet hormone release. Both donors
dose dependently inhibited glucose-stimulated insulin release and induced modest (hydroxylamine) or profound (tert-butylhydroperoxide) suppression of 45Ca2+-efflux from perifused islets. By contrast, both donors stimulated glucagon release. Similar effects on hormone release were
displayed after K+-depolarization. Insulin and glucagon release stimulated by activation of the cAMP system through isobutylmethylxanthine (IBMX)
at basal glucose was modestly potentiated by low concentrations of both donors. These effects were still observed, although
less pronounced, in K+-depolarized islets. In vitro as well as in vivo, the NO-synthase inhibitor NG-nitro-L-arginine methyl ester inhibited IBMX-induced glucagon release, but did not affect insulin release. The results suggest
that NO and hydroperoxide inhibit glucose-stimulated insulin release by perturbing Ca2+ fluxes and probably acting through S-nitrosylation (NO) or oxidation (hydroperoxide) of thiol groups critical to the secretory process. These effects are largely
independent of depolarization events. By contrast, both NO and hydroperoxide can potentiate cAMP-stimulated hormone release
presumably at a distal site in the stimulus-secretion coupling. 相似文献
17.
A mathematical model of vasoreactivity in rat mesenteric arterioles: I. Myoendothelial communication
Adam Kapela Anastasios Bezerianos Nikolaos M. Tsoukias 《Microcirculation (New York, N.Y. : 1994)》2009,16(8):694-713
To study the effect of myoendothelial communication on vascular reactivity, we integrated detailed mathematical models of Ca2+ dynamics and membrane electrophysiology in arteriolar smooth muscle (SMC) and endothelial (EC) cells. Cells are coupled through the exchange of Ca2+, Cl?, K+, and Na+ ions, inositol 1,4,5‐triphosphate (IP3), and the paracrine diffusion of nitric oxide (NO). EC stimulation reduces intracellular Ca2+ ([Ca2+ in the SMC by transmitting a hyperpolarizing current carried primarily by K+. The NO‐independent endothelium‐derived hyperpolarization was abolished in a synergistic‐like manner by inhibition of EC SKCa and IKCa channels. During NE stimulation, IP3diffusing from the SMC induces EC Ca2+ release, which, in turn, moderates SMC depolarization and [Ca2+]i elevation. On the contrary, SMC [Ca2+]i was not affected by EC‐derived IP3. Myoendothelial Ca2+ fluxes had no effect in either cell. The EC exerts a stabilizing effect on calcium‐induced calcium release‐dependent SMC Ca2+ oscillations by increasing the norepinephrine concentration window for oscillations. We conclude that a model based on independent data for subcellular components can capture major features of the integrated vessel behavior. This study provides a tissue‐specific approach for analyzing complex signaling mechanisms in the vasculature. 相似文献
18.
Reactive oxygen species (ROS) and intracellular Ca2+ overload play key roles in myocardial ischemia-reperfusion (IR) injury but the relationships among ROS, Ca2+ overload and LV mechanical dysfunction remain unclear. We tested the hypothesis that H2O2 impairs LV function by causing Ca2+ overload by increasing late sodium current (INa), similar to Sea Anemone Toxin II (ATX-II). Diastolic and systolic Ca2+ concentrations (d[Ca2+]i and s[Ca2+]i) were measured by indo-1 fluorescence simultaneously with LV work in isolated working rat hearts. H2O2 (100 μM, 30 min) increased d[Ca2+]i and s[Ca2+]i. LV work increased transiently then declined to 32% of baseline before recovering to 70%. ATX-II (12 nM, 30 min) caused greater increases in d[Ca2+]i and s[Ca2+]i. LV work increased transiently before declining gradually to 17%. Ouabain (80 μM) exerted similar effects to ATX-II. Late INa inhibitors, lidocaine (10 μM) or R56865 (2 μM), reduced effects of ATX-II on [Ca2+]i and LV function, but did not alter effects of H2O2. The antioxidant, N-(2-mercaptopropionyl)glycine (MPG, 1 mM) prevented H2O2-induced LV dysfunction, but did not alter [Ca2+]i. Paradoxically, further increases in [Ca2+]i by ATX-II or ouabain, given 10 min after H2O2, improved function. The failure of late INa inhibitors to prevent H2O2-induced LV dysfunction, and the ability of MPG to prevent H2O2-induced LV dysfunction independent of changes in [Ca2+]i indicate that impaired contractility is not due to Ca2+ overload. The ability of further increases in [Ca2+]i to reverse H2O2-induced LV dysfunction suggests that Ca2+ desensitization is the predominant mechanism of ROS-induced contractile dysfunction. 相似文献
19.
Cardiac glycosides, which inhibit the plasma membrane Na+ pump, are one of the four categories of drug recommended for routine use to treat heart failure, yet their therapeutic window is limited by toxic effects. Elevated cytoplasmic Na+ ([Na+]i) compromises mitochondrial energetics and redox balance by blunting mitochondrial Ca2+ ([Ca2+]m) accumulation, and this impairment can be prevented by enhancing [Ca2+]m. Here, we investigate whether this effect underlies the toxicity and arrhythmogenic effects of cardiac glycosides and if these effects can be prevented by suppressing mitochondrial Ca2+ efflux, via inhibition of the mitochondrial Na+/Ca2+ exchanger (mNCE). In isolated cardiomyocytes, ouabain elevated [Na+]i in a dose-dependent way, blunted [Ca2+]m accumulation, decreased the NADH/NAD + redox potential, and increased reactive oxygen species (ROS). Concomitant treatment with the mNCE inhibitor CGP-37157 ameliorated these effects. CGP-37157 also attenuated ouabain-induced cellular Ca2+ overload and prevented delayed afterdepolarizations (DADs). In isolated perfused hearts, ouabain's positive effects on contractility and respiration were markedly potentiated by CGP-37157, as were those mediated by β-adrenergic stimulation. Furthermore, CGP-37157 inhibited the arrhythmogenic effects of ouabain in both isolated perfused hearts and in vivo. The findings reveal the mechanism behind cardiac glycoside toxicity and show that improving mitochondrial Ca2+ retention by mNCE inhibition can mitigate these effects, particularly with respect to the suppression of Ca2+-triggered arrhythmias, while enhancing positive inotropic actions. These results suggest a novel strategy for the treatment of heart failure. 相似文献
20.
Pancreatic β-cells from obese-hyperglycemic (ob/ob) mice are widely used for studying the mechanisms of insulin release, including its regulation by the cytoplasmic Ca2+ concentration ([Ca2+]i). In this study, we compared changes of [Ca2+]i in single β-cells isolated from ob/ob mice with those from lean mice using dual-wavelength microfluorometry and the indicator fura-2. There were no differences
in the frequency, amplitude, and half-width of the slow oscillations induced by glucose. Most β-cells from the obese mice
responded to 10 mM caffeine with transformation of the oscillations into sustained elevation of [Ca2+]i, a process counteracted by ryanodine. The β-cells from the obese mice were characterized by ample generation of [Ca2+]i transients, which increased in number in the presence of glucagon. The transients became less frequent when leptin was added
at a concentration as low as 1 nM. It is suggested that the excessive firing of [Ca2+]i transients in the ob/ob mice is owing to the absence of leptin and is mediated by activation of the phospholipase C signaling pathway. 相似文献