共查询到20条相似文献,搜索用时 31 毫秒
1.
J. V. Nadler W. F. White K. W. Vaca Dianna A. Redburn C. W. Cotman 《Journal of neurochemistry》1977,29(2):279-290
Abstract— Superfused slices of the rat dentate gyrus were employed to study the release of GABA, glutamate and aspartate, which are considered strong neurotransmitter candidates in this region. The introduction of Ca2+ to a Ca2+-free superfusion medium containing a depolarizing agent augmented the efflux of all three amino acids. The response to application of Ca2+ nearly always occurred within 30 s, the shortest interval tested in these studies. The efflux rate reached a peak within 90 s and then declined to a level slightly greater than the prestimulation baseline. The failure to maintain the maximal rate with continued exposure to Ca2+ and depolarizing influences appeared not to result from a reduction in Ca2+ permeability caused by continuous depolarization. Ca2+ also stimulated the efflux of exogenously loaded radiolabeled GABA, glutamate and aspartate, but not proline. Exogenously loaded GABA was more readily released than endogenous GABA. Otherwise the effects of various treatments on their efflux rates were qualitatively similar. Mg2+ inhibited Ca2+-dependent efflux. Ba2+, but not Mg2+, stimulated amino acid efflux in the absence of Ca2+. Extracellular Na+ was not required to support Ca2+-dependent efflux. Addition of Ca2+ to a Ca2+-free medium in the absence of a depolarizing agent released GABA from the slices, but not glutamate or aspartate. K+-enriched medium and the depolarizing alkaloid, veratridine, stimulated both Ca2+-dependent and Ca2+-independent release processes. Na+-free medium enhanced the Ca2+-independent releasing action of elevated K+. Ca2+-independent release was inhibited by raising the Mg2+ concentration by 15 or 30 mM and appeared to be inhibited by Ca2+ as well. Amino acid output in the absence of Ca2+ is probably not directly related to transmission and is considered to result partially from a general increase in membrane permeability induced by depolarization in a Ca2+-free medium and partially from stimulation of carrier-mediated amino acid efflux. These results support previously suggested transmitter roles for GABA, glutamate and aspartate in the rat dentate gyrus. 相似文献
2.
The mechanism of the protective effect of Ca2+ on cellular K+ content was studied by examination of the effect of Ca2+ on efflux of the K+ analog, 86Rb+, from preloaded cells with the use of compounds which interfere with monovalent cation movements. Ca2+ decreased 86Rb+ efflux to the same extent in the presence and absence of ouabain, suggesting that Ca2+ did not alter the activity of the (Na+ + K+)-adenosine triphosphatase pump. Ca2+ exerted a similar protective effect in the presence of furosemide, an inhibitor of K+-K+ exchange, indicative that Ca2+ was not inhibiting this pathway. Since Ca2+ did not influence these pathways, it is concluded that Ca2+ exerts its primary effect by slowing passive diffusion. In support of this, Ca2+ also slowed 22Na+ efflux. In addition, ethanol-induced leakage of 86Rb+ was reversed by extracellular Ca2+, suggestive of a Ca2+-membrane phospholipid interaction. 相似文献
3.
We have previously reported on the biochemical properties of a Na+,K+,2Cl?-cotransport in HeLa cells and here we deal with aspects of its physiological regulation. Na+,K+,2Cl?-cotransport in HeLa cells was studied by 86Rb+ influx and 86Rb+/22Na+ efflux measurements. The effects of rat atrial natriuretic peptide (ANP), isoproterenol, and amino acids on 86Rb+ flux, mediated by the bumet-anide-sensitive Na+, K+, 2Cl?-cotransport system and the ouabain-sensitive Na+/K+-pump, were investigated. ANP reduced bumetanide-sensitive 86Rb+ influx under isotonic as well as under hypertonic conditions. Similar decrease of bumetanide-sensitive 86Rb+ influx was observed in the presence of 8-bromo-cGMP, while neither isoproterenol as a β-receptor agonist nor 8-bromo-cAMP-could alter bumetanide-sensitive 86Rb+ influx. Furthermore, efflux of 86Rb+ and 22Na+ was greatly reduced in the presence of bumetanide and ANP. Together with our recent findings, showing functionally active, high affinity receptors for ANP on HeLa cells (Kort and Koch, Biochim. Biophys. Res. Commun. 168:148–154, 1990), this study indicates that ANP participates in the regulation of the Na+, K+, 2Cl?-cotransport system in HeLa cells. Further measurements revealed that amino acids as present in the growth medium (Joklik's minimal essential medium) and the amino acid derivative α-methyl-aminoisobutyric acid (metAlB, 1 and 5 mM, respectively) also reduced Na+, K+, 2Cl?-cotransport-mediated 86Rb+ uptake and diminished the stimulatory effect of hypertonicity on the cotransporter. In addition, the Na+/K+-pump was markedly stimulated in the presence of amino acids, while neither ANP and 8-Br-cGMP nor isoproterenol and 8-Br-cAMP had a significant effect on the activity of the Na+/K+-pump. 相似文献
4.
Anita M. Hennige Nicolas Lembert Martin A. Wahl Hermann P.T. Ammon 《Free radical research》2013,47(5):507-516
Oxidative stress to B-cells is thought to be of relevance in declining B-cell function and in the process of B-cell destruction. In other tissues including heart, brain and liver, oxidative stress has been shown to elevate the intracellular free calcium concentration and to provoke potassium efflux. We studied the effect of oxidative stress on Ca2+ and K+ (Rb+) outflow from pancreatic islets using the thiol oxidants DIP and BuOOH. Both compounds reversibly increased 86Rb+ efflux in the presence of 3 and 16.7 mmol/l glucose. Stimulation of 86Rb+ efflux was also evident in the absence of calcium. DIP evoked release of 45Ca2+ from the pancreatic islets both in the presence or absence of extracellular calcium. Employing inhibitors of the calcium-activated potassium channel (KCa) and the high conductance K+-channel (BKCa), the effect of DIP on 86Rb+ efflux was slightly diminished. Tolbutamide had no effect on 86Rb+ efflux in the presence of DIP. On the other hand thapsigargin, a blocker of the Ca2+-ATPase of the endoplasmic reticulum, completely suppressed the DIP-mediated 86Rb+ outflow. The data suggest that thiol oxidant-induced potassium efflux from pancreatic islets is mainly mediated through liberation of intracellular calcium and subsequent stimulation of calcium-activated potassium efflux. 相似文献
5.
F R Butcher 《Life sciences》1979,24(21):1979-1982
Stimulation of 86Rb+ efflux from isolated parotid acinar cells by carbchol was biphasic. The phases of stimulated 86Rb+ efflux were separated on the basis of their relative requirements for extracellular Ca2+. If the isolated cells were incubated in Ca2+ free buffer containing 1.0 mM ethylene glycol bis (β-aminoethyl ether) N, N1 - tetra acetic acid (EGTA) for 30 min. before adding carbachol an initial phase of 86Rb+ efflux was observed. A second phase of 86Rb+ efflux was obtained upon addition of 2.0 mM Ca2+. However when cells were incubated for 60 min. in Ca2+ free buffer containing 1.0 mM EGTA the initial phase of release caused by carbachol was inhibited by 95 percent. If the EGTA was titrated with Ca2+ to give 1.0 mM Ca2+, following the 60 min. depletion regimen, the second phase was observed. Although 60 min. of Ca2+-depletion in EGTA buffer was required for complete inhibition of the effect of carbachol on the initial phase of 86Rb+ efflux, the response was fully restored within 4 min. after the readdition of Ca2+. 相似文献
6.
Maria Elena Sandoval 《Journal of neurochemistry》1980,35(4):915-921
It has been suggested that mitochondria might modify transmitter release through the control of intracellular Ca2+levels. Treatments known to inhibit Ca2+retention by mitochondria lead to an increased transmitter liberation in the absence of external Ca2+, both at the frog neuromuscular junction and from isolated nerve endings. Sodium ions stimulate Ca2+efflux from mitochondria isolated from excitable tissues. In the present study, the effect of increasing internal Na+ levels on [3H]γ-aminobutyric acid ([3H]GABa) release from isolated nerve endings is reported. Results show that the efflux of [3H]GABA from prelabeled synaptosomes is stimulated by ouabain, veratrine, gramicidin D, and K+-free medium, which increase the internal sodium concentration. This effect was not observed when Na+ was omitted from the incubation medium and it was independent of external Ca2+, the experiments having been performed in a Ca2+-free, EGTA-containing medium. Since preincubation of synaptosomes with 2,4-diaminobutyric acid did not prevent the stimulatory effect of increased internal Na+ levels on [3H]GABA efflux, it appears to be unrelated to an enhanced activity of the outward carrier-mediated GABA transport. These results suggest that the augmented release of [3H]GABA may be due to an increased Ca2+efflux from mitochondria eiicited by the accumulation of Na+ at the nerve endings. Sandoval M. E. Sodium-dependent efflux of [3H]GABA from synaptosomes probably related to mitochondrial calcium mobilization. J. Neurochem. 35 , 915–921 (1980). 相似文献
7.
Distinct effects of acetylcholine and glucose on 45calcium and 86rubidium efflux from mouse pancreatic islets 总被引:1,自引:0,他引:1
The similarities between the effects of acetylcholine and glucose on phospholipid metabolism in pancreatic islet cells prompted the comparison of their effects on ionic fluxes. Acetylcholine (1 μM) consistently increased 45Ca2+ efflux from mouse islets, whereas glucose increased it in the presence, but decreased it in the absence of extracellular Ca2+. Acetylcholine consistently accelerated 86Rb+ efflux, and this effect was augmented by Ca2+ omission. On the other hand, glucose markedly inhibited 86Rb+ efflux, except when its concentration was raised from 10 to 15 mM in the presence of Ca2+. Unlike their effects on phospholipid metabolism, the ionic effects of the two insulin-secretagogues are thus very different. 相似文献
8.
Abstract: The potent nicotinic agonist anatoxin-a elicits mecamylamine-sensitive [3H]dopamine release from striatal synaptosomes, and this action is both Na+ and Ca2+ dependent and is blocked by Cd2+. This suggests that stimulation of presynaptic nicotinic receptors results in Na+ influx and local depolarisation that activates voltage-sensitive Ca2+ channels, which in turn provide the Ca2+ for exocytosis. Here we have investigated the subtypes of Ca2+ channels implicated in this mechanism. [3H]Dopamine release evoked by anatoxin-a (1 µM) was partially blocked by 20 µM nifedipine, whereas KCl-evoked release was insensitive to the dihydropyridine. However, a 86Rb+ efflux assay of nicotinic receptor function suggested that nifedipine has a direct effect on the receptor, discrediting the involvement of L-type channels. The N-type Ca2+ channel blocker ω-conotoxin GVIA (1 µM) blocked anatoxin-a-evoked [3H]dopamine release by 60% but had no significant effect on 86Rb+ efflux; release evoked by both 15 and 25 mM KCl was inhibited by only 30%. The P-type channel blocker ω-agatoxin IVA (90 nM) also inhibited KCl-evoked release by ~30%, whereas anatoxin-a-evoked release was insensitive. The Q-type channel blocker ω-conotoxin MVIIC (1 µM) had no effect on either stimulus. These results suggest that presynaptic nicotinic receptors on striatal nerve terminals promote [3H]dopamine release by activation of N-type Ca2+ channels. In contrast, KCl-evoked [3H]dopamine release appears to involve both N-type and P-type channels. 相似文献
9.
Shmuel Muallem Timothy Beeker Stephen J. Pandol 《The Journal of membrane biology》1988,102(2):153-162
Summary The relative contributions of the Na+/Ca2+ exchange and the plasma membrane Ca2+ pump to active Ca2+ efflux from stimulated rat pancreatic acini were studied. Na+ gradients across the plasma membrane were manipulated by loading the cells with Na+ or suspending the cells in Na+-free media. The rates of Ca2+ efflux were estimated from measurements of [Ca2+]
i
using the Ca2+-sensitive fluorescent dye Fura 2 and45Ca efflux. During the first 3 min of cell stimulation, the pattern of Ca2+ efflux is described by a single exponential function under control, Na+-loaded, and Na+-depleted conditions. Manipulation of Na+ gradients had no effect on the hormone-induced increase in [Ca2+]
i
. The results indicate that Ca2+ efflux from stimulated pancreatic acinar cells is mediated by the plasma membrane Ca2+ pump. The effects of several cations, which were used to substitute for Na+, on cellular activity were also studied. Choline+ and tetramethylammonium+ (TMA+) released Ca2+ from intracellular stores of pancreatic acinar, gastric parietal and peptic cells. These cations also stimulated enzyme and acid secretion from the cells. All effects of these cations were blocked by atropine. Measurements of cholecystokinin-octapeptide (CCK-OP)-stimulated amylase release from pancreatic acini, suspended in Na+, TMA+, choline+, or N-methyl-d-glucamine+ (NMG+) media containing atropine, were used to evaluate the effect of the cations on cellular function. NMG+, choline+, and TMA+ inhibited amylase release by 55, 40 and 14%, respectively. NMG+ also increased the Ca2+ permeability of the plasma membrane. Thus, to study Na+ dependency of cellular function, TMA+ is the preferred cation to substitute for Na+. The stimulatory effect of TMA+ can be blocked by atropine. 相似文献
10.
A C Boschero S Kawazu A Sener A Herchuelz W J Malaisse 《Archives of biochemistry and biophysics》1979,196(1):54-63
In isolated rat pancreatic islets, valinomycin (0.01 to 1.0 μm) caused a dose-related facilitation of 86Rb+ outflow and a dose-related inhibition of the glucose-induced changes in both outflow and net uptake of 86Rb+. At high concentrations (0.1–1.0 μm), the ionophore also inhibited the oxidation of glucose and endogenous nutrients, decreased the adenylate charge, and lowered the concentration of reduced pyridine nucleotides in the islet cells. However, as little at 1.0 to 10.0 nm valinomycin caused anomalies in the handling of 45Ca2+ (suppression of the early inhibitory effect of glucose upon 45Ca2+ efflux, and reduction in the amount of 45Ca2+ recovered in the islets after an extensive washing procedure) and inhibition of insulin release. Moreover, when the effect of glucose upon K+ conductance was abolished by high concentrations of valinomycin (0.1–1.0 μm), the glucose-induced secondary rise in 45Ca2+ efflux was still observed. These findings suggest that the effects of glucose upon 86Rb+ and 45Ca2+ handling, respectively, although normally concomitant with one another, can be dissociated, in part at least, from one another. It is concluded that the glucose-induced reduction in K+ outflow may be unnecessary for the sugar to cause a partial remodeling of Ca2+ fluxes in the islet cells. 相似文献
11.
Summary
86Rb+ fluxes have been measured in suspensions of vesicles prepared from the epithelium of toad urinary bladder. A readily measurable barium-sensitive, ouabain-insensitive component has been identified; the concentration of external Ba2+ required for half-maximal inhibition was 0.6mm. The effects of externally added cations on86Rb+ influx and efflux have established that this pathway is conductive, with a selectivity for K+, Rb+ and Cs+ over Na+ and Li+. the Rb+ uptake is inversely dependent on external pH, but not significantly affected by internal Ca2+ or external amiloride, quinine, quinidine or lidocaine. It is likely, albeit not yet certain, that the conductive Rb+ pathway is incorporated in basolateral vesicles oriented right-side-out. It is also not yet clear whether this pathway comprises the principle basolateral K+ channel in vivo, and that its properties have been unchanged during the preparative procedures. Subject to these caveats, the data suggest that the inhibition by quinidine of Na+ transport across toad bladder does not arise primarily from membrane depolarization produced by a direct blockage of the basolateral channels. It now seems more likely that the quinidine-induced elevation of intracellular Ca2+ activity directly blocks apical Na+ entry. 相似文献
12.
Marunaka Y Niisato N O'Brodovich H Post M Tanswell AK 《The Journal of membrane biology》1999,168(1):91-101
The aim of the present study was to investigate the roles of Ca2+ and protein tyrosine kinase (PTK) in the insulin action on cell volume in fetal rat (20-day gestational age) type II pneumocytes.
Insulin (100 nm) increased cell volume in the presence of extracellular Ca2+ (1 mm), while cell shrinkage was induced by insulin in the absence of extracellular Ca2+ (<1 nm). This insulin action in a Ca2+-containing solution was completely blocked by co-application of bumetanide (50 μm, an inhibitor of Na+/K+/2Cl− cotransporter) and amiloride (10 μm, an inhibitor of epithelial Na+ channel), but not by the individual application of either bumetanide or amiloride. On the other hand, the insulin action
on cell volume in a Ca2+-free solution was completely blocked by quinine (1 mm, a blocker of Ca2+-activated K+ channel), but not by bumetanide and/or amiloride. These observations suggest that insulin activates an amiloride-sensitive
Na+ channel and a bumetanide-sensitive Na+/K+/2Cl− cotransporter in the presence of 1 mm extracellular Ca2+, that the stimulatory action of insulin on an amiloride-sensitive Na+ channel and a bumetanide-sensitive Na+/K+/2Cl− cotransporter requires Ca2+, and that in a Ca2+-free solution insulin activates a quinine-sensitive K+ channel but not in the presence of 1 mm Ca2+. The insulin action on cell volume in a Ca2+-free solution was almost completely blocked by treatment with BAPTA (10 μm) or thapsigargin (1 μM, an inhibitor of Ca2+-ATPase which depletes the intracellular Ca2+ pool). Further, lavendustin A (10 μm, an inhibitor of receptor type PTK) blocked the insulin action in a Ca2+-free solution. These observations suggest that the stimulatory action of insulin on a quinine-sensitive K+ channel is mediated through PTK activity in a cytosolic Ca2+-dependent manner. Lavendustin A, further, completely blocked the activity of the Na+/K+/2Cl− cotransporter in a Ca2+-free solution, but only partially blocked the activity of the Na+/K+/2Cl− cotransporter in the presence of 1 mm Ca2+. This observation suggests that the activity of the Na+/K+/2Cl− cotransporter is maintained through two different pathways; one is a PTK-dependent, Ca2+-independent pathway and the other is a PTK-independent, Ca2+-dependent pathway. Further, we observed that removal of extracellular Ca2+ caused cell shrinkage by diminishing the activity of the amiloride-sensitive Na+ channel and the bumetanide-sensitive Na+/K+/2Cl− cotransporter, and that removal of extracellular Ca2+ abolished the activity of the quinine-sensitive K+ channel. We conclude that the cell shrinkage induced by removal of extracellular Ca2+ results from diverse effects on the cotransporter and Na+ and K+ channels.
Received: 2 September 1998/Revised: 30 November 1998 相似文献
13.
The effect of glucose on the Ca2+-activated K+ permeability in pancreatic islet cells was investigated by measuring the rate of 86Rb efflux, 45Ca efflux and insulin release from perifused rat pancreatic islets exposed to step-wise increased in glucose concentration. When the glucose concentration was raised from intermediate (8.3 or 11.1 mM) to higher values, a rapid and sustained increase in 86Rb outflow, 45Ca outflow and insulin release was observed. Likewise, in the presence of 8.3 or 16.7 mM glucose, tolbutamide increased 86Rb and 45Ca efflux, as well as insulin release. In the two series of experiments, a tight correlation was found between the magnitude of the changes in 86Rb and 45Ca outflow, respectively. It is concluded that, at variance with current ideas, glucose does not inhibit the response to cytosolic Ca2+ of the Ca2+-sensitive modality of K+ extrusion. On the contrary, as a result of its effect upon Ca2+ handling, glucose stimulates the Ca2+-activated K+ permeability. 相似文献
14.
The release of several endogenous amino acids and adenosine from rat cerebellar neuronal cultures following elevated K+ exposure in the presence and absence of added Ca2+ was studied. The amino acids aspartate (ASP), glutamate (GLU) and GABA were released from the cultures in a dose- and Ca2+-dependent manner. Taurine (TAU) and the nucleoside adenosine (ADN) efflux rates were dose-dependent but Ca2+-independent, and basal levels increased in the absence of Ca2+. The K+ depolarization induced release of serine (SER), alanine (ALA) and proline (PRO), was not dose-dependent and in the absence of extracellular Ca2+ (with added Mg2+) higher basal release of SER and ALA, but not PRO, was noted. These findings demonstrate that in addition to known cerebellar neurotransmitters, other neuroactive and neutral amino acids are released from cultured cerebellar neurons in response to K+ depolarization. Their observed efflux suggests they may have as yet unidentified roles in neuronal function with different classes of efflux corresponding to: neurotransmitter-type release (ASP, GLU, GABA), and osmoregulatory, possibly neuromodulatory-type release (TAU), a Ca2+-insensitive, possibly neuromodulatory-type release (ADN), and a depolarization-sensitive release (SER, ALA, PRO) of which SER and ALA are partially Ca2+-sensitive. 相似文献
15.
Sylvia Lindberg 《Physiologia plantarum》1990,79(2):275-282
Three cultivars of sugar beet (Beta vulgaris L.), which are sensitive to aluminium (Al) in the order Primahill > Monohill > Regina, were grown in water culture for 2 weeks. Nutrients were supplied at 15% increase of amounts daily, corresponding to the nutrient demand for maximal growth. The 2.4-dinitrophenol (DNP)-sensitive (metabolic) and DNP-insensitive (non-metabolic) uptake of aluminium, phosphate. 45Ca2+ and K+(86Rb+) in roots were measured as well as transport to shoots of intact plants. All 3 cultivars absorbed more aluminium if DNP was present during the aluminium treatment than in its absence. It is suggested that sugar beets are able to extrude aluminium activity or that they possess an active mechanism to keep Al outside the cell. The presence of Al in the medium during the 1-h experiment affected the metabolic and non-metabolic fluxes of 45Ca2+ and K+(86Rb+) in different ways. In the presence of DNP, the influx of both 45Ca2+ and K+(86Rb+) and the efflux of 45Ca2+ were inhibited by Al in a competitive way. At inhibition of 45Ca2+ influx, 2 Al ions are probably bound per Ca2+ uptake site in cv. Regina (Al-tolerant), but in cvs Primahill and Monohill only one Al ion is bound (more Al sensitive). Aluminium competitively inhibited the active efflux of 45Ca2+ (absence of DNP) in almost the same way in the 3 cultivars. In contrast, aluminium stimulated the influx of K+(86Rb+) in cvs Primahill, Monohill and Regina in the absence of DNP. Thus, the Al effects on active and passive K+(86Rb+) influx are different. The total influx of K+(86Rb+) increased in the presence of Al and might be connected to an active exclusion of Al. Regina is the least Al-sensitive cultivar, probably because Al interferes less with the Ca2+ fluxes and because this cultivar actively excludes phosphate in the presence of Al. Thus Al-phosphate precipitation within the plant could be avoided. 相似文献
16.
Fernando Soler Paz Sanchez-Migallon Juan C. Gomez-Fernandez Francisco Fernandez-Belda 《Journal of bioenergetics and biomembranes》1994,26(1):127-136
The release of H+ during the oxalate-supported Ca2+ uptake in sarcoplasmic reticulum vesicles is kinetically coincident with the initial phase of Ca2+ accumulation. The Ca2+ uptake is increased and the H+ release is decreased in the presence of KCl and other monovalent chloride salts as expected for a H+-monovalent cation exchange. The functioning of the Ca2+-pump is disturbed by the presence of potassium gluconate and, to a lesser extent, of choline chloride. These salts do not inhibit the ATPase activity of Ca2+-permeable vesicles, suggesting a charge imbalance inhibition which is specially relevant in the case of gluconate. Therefore, K+, and also Cl–, appear to be involved in secondary fluxes during the active accumulation of Ca2+. The microsomal preparation seems homogeneous with respect to the K+-channel, showing an apparent rate constant for K+ release of approximately 25 s–1 measured with the aid of86Rb+ tracer under equilibrium conditions. A Rb+ efflux, sensitive to Ca2+-ionophore, can be also detected during the active accumulation of Ca2+. The experimental data suggest that both monovalent cations and anions are involved in a charge compensation during the Ca2+ uptake and H+ release. Fluxes of these highly permeable ions would contribute to cancel the formation of a resting membrane potential through the sarcoplasmic reticulum membrane. 相似文献
17.
The effects of 5-hydroxytryptamine and 5-hydroxytryptophan on 86Rb+ efflux from prelabelled ob/ob-mouse islets were studied to better understand the cellular mechanisms underlying the effects of 5-hydroxytryptamine and 5-hydroxytryptophan on insulin release. 5-Hydroxytryptophan (4 mM) had no effect on 86Rb+ efflux either at a low (3 mM) or at a high (20 mM) d-glucose concentration, whereas 5-hydroxytryptamine (4 mM) stimulated 86Rb+ efflux at both glucose concentrations. These results indicate that 5-hydroxytryptamine may reduce glucose-induced insulin release by inhibiting early steps in the β-cell stimulus-secretion coupling. 相似文献
18.
Jaipaul Singh 《生物化学与生物物理学报:生物膜》1984,775(1):77-85
The effect of acetylcholine and the cholecystokinin-like peptide, caerulein on the fractional efflux of 86Rb+ from preloaded isolated segments of mouse pancreas were studied. Both secretagogues evoked a marked transient increase in 86Rb+ efflux. The removal of Ca2+ from the superfusing medium and addition of 10?4 M EGTA, markedly reduced, but did not abolish the responses to either acetylcholine or caerulein. Furosemide () or piretanide (10?4 M) reduced the basal efflux and inhibited the secretagogue-elicited responses. Stimulus-induced 86Rb+ outflow was abolished when the Cl? component of the superfusing solution was replaced by either NO3?, SO42? or I? but not in case of replacement by Br?, When Na+ was replaced with either Li+ or choline+ both acetylcholine and caerulein failed to elicit any detectable increase in 86Rb+ outflow. However, when Tris+ was substituted for Na+, acetylcholine caused a moderate increase in 86Rb+ efflux which was abolished by either furosemide (10?4 M) or chloride depletion (nitrate substitution). The removal of extracellular K+ or pretreatment with 10?3 M ouabain had little effect on secretagogue-evoked 86Rb+ efflux. These results indicate the presence of a diuretic-sensitive Na+-K+-Cl? cotransport system in the mouse pancreatic acinar cell membrane. 相似文献
19.
Abstract: The effects of four K+-channel inhibitors on synaptosomal free Ca2+ concentrations and 86Rb+ fluxes are analysed. 4-Aminopyridine, α-dendrotoxin, charybdotoxin, and tetraethylammonium all increase the free Ca2+ concentration, although their potencies differ widely. In each case, the elevation in free Ca2+ concentration is reversed by the subsequent addition of tetrodotoxin. The transient 86Rb+ efflux from preequilibrated synaptosomes induced with high concentrations of veratridine is partially inhibited by 4-aminopyridine and α-dendrotoxin. In contrast, when 4-aminopyridine or α-dendrotoxin is added to polarized synaptosomes, an enhanced86Rb+ flux is seen, both for uptake and for efflux with no change in the total 86Rb+/K+ content of the synaptosomes and with only a slight time-averaged plasma membrane depolarization (6.4 and 3.3 mV, respectively). The enhancements of flux by 4-aminopyridine or α-dendrotoxin are sensitive to ouabain and/or to tetrodotoxin. Furthermore, these flux changes show the same concentration dependencies as the blocked component of veratridine-stimulated 86Rb+ efflux, the elevation of free Ca2+ concentration, and the facilitation of glutamate exocytosis that are elicited by 4-aminopyridine or α-dendrotoxin. It is concluded that these findings support the proposal of spontaneous, repetitive firing of synaptosomes evoked by K+-channel inhibitors and that the enhanced 86Rb+ flux is a consequence of the activity of 4-aminopyridine- and α-dendrotoxin-insensitive K+ channels during these action potentials. 相似文献
20.
Per Lindström Janove Sehlin 《Biochimica et Biophysica Acta (BBA)/Molecular Cell Research》1982,720(4):400-404
The effects of 5-hydroxytryptamine and 5-hydroxytryptophan on 86Rb+ efflux from prelabelled ob/ob-mouse islets were studied to better understand the cellular mechanisms underlying the effects of 5-hydroxytryptamine and 5-hydroxytryptophan on insulin release. 5-Hydroxytryptophan (4 mM) had no effect on 86Rb+ efflux either at a low (3 mM) or at a high (20 mM) d-glucose concentration, whereas 5-hydroxytryptamine (4 mM) stimulated 86Rb+ efflux at both glucose concentrations. These results indicate that 5-hydroxytryptamine may reduce glucose-induced insulin release by inhibiting early steps in the β-cell stimulus-secretion coupling. 相似文献