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1.
Naranjan S. Dhalla Vincenzo Panagia Naoki Makino Robert E. Beamish 《Molecular and cellular biochemistry》1988,82(1-2):75-79
In order to identify defects in Na+-Ca2+ exchange and Ca2+-pump systems in cardiomyopathic hearts, the activities of sarcolemmal Na+-dependent Ca2+ uptake, Na+-induced Ca2+ release, ATP-dependent Ca2+ uptake and Ca2+-stimulated ATPase were examined by employing cardiomyopathic hamsters (UM-X7.1) and catecholamine-induced cardiomyopathy produced by injecting isoproterenol into rats. The rates of Na+-dependent Ca2+ uptake, ATP-dependent Ca2+ uptake and Ca2+-stimulated ATPase activities of sarcolemmal vesicles from genetically-linked cardiomyopathic as well as catecholamine-induced cardiomyopathic hearts were decreased without any changes in Na+-induced Ca2+-release. Similar results were obtained in Ca2+-paradox when isolated rat hearts were perfused for 5 min with a medium containing 1.25 mM Ca2+ following a 5 min perfusion with Ca2+-free medium. Although a 2 min reperfusion of the Ca2+-free perfused hearts depressed sarcolemmal Ca2+-pump activities without any changes in Na+-induced Ca2+-release, Na+-dependent Ca2+ uptake was increased. These results indicate that alterations in the sarcolemmal Ca2+-efflux mechanisms may play an important role in cardiomyopathies associated with the development of intracellular Ca2+ overload. 相似文献
2.
Modification of heart sarcolemmal Na+/K+-ATPase activity during development of the calcium paradox 总被引:3,自引:0,他引:3
This study examined the status of sarcolemmal Na+/K+-ATPase activity in rat heart under conditions of Ca2+-paradox to explore the existence of a relationship between changes in Na+/K+-pump function and myocardial Na+ as well as K+ content. One min of reperfusion with Ca2+ after 5 min of Ca2+-free perfusion reduced Na+/K+-ATPase activity in the isolated heart by 53% while Mg2+-ATPase, another sarcolemmal bound enzyme, retained 74% of its control activity. These changes in sarcolemmal ATPase activities were dependent on the duration and Ca2+ concentration of the initial perfusion and subsequent reperfusion periods; however, the Na+/K+-ATPase activity was consistently more depressed than Mg2+-ATPase activity under all conditions. The depression in both enzyme activities was associated with a reduction in Vmax without any changes in Km values. Low Na+ perfusion and hypothermia, which protect the isolated heart from the Ca2+-paradox, also prevented reperfusion-induced enzyme alterations. A significant relationship emerged upon comparison of the changes in myocardial Na+ and K+ content to Na+/K+-ATPase activity under identical conditions. At least 60% of the control enzyme activity was necessary to maintain normal cation gradients. Depression of the Na+/K+-ATPase activity by 60-65% resulted in a marked increase and decrease in intracellular Na+ and K+ content, respectively. These results suggest that changes in myocardial Na+ and K+ content during Ca2+-paradox are related to activity of the Na+/K+-pump; the impaired Na+/K+-ATPase activity may lead to augmentation of Ca2+-overload via an enhancement of the Na+/Ca2+-exchange system. 相似文献
3.
Langford MP Chen D Welbourne TC Redens TB Ganley JP 《Molecular and cellular biochemistry》2002,232(1-2):63-73
In order to understand the modification of -adrenoceptor linked signal transduction by changes in the intracellular Ca2+, we examined the status of -adrenoceptors (-ARs), G-proteins and adenylyl cyclase (AC) in Ca2+-deficiency and Ca2+-overload by perfusing the isolated rat heart with Ca2+-free medium for 5 min and Ca2+-containing medium for 5 min following Ca2+-free perfusion, respectively. Ca2+-depletion caused not only an increase in basal, isoproterenol-, Gpp(NH)p-, NaF- and forskolin-stimulated AC activities but also produced an increase in the 1-AR affinity and density as well as up-regulation of Gs-protein function and uncoupling of Gi-protein to AC. Ca2+-repletion for 5 min following 5 min Ca2+-free perfusion reversed the increased AC activities to varying degrees. The 1-AR affinity was further increased upon Ca2+-repletion whereas its density was decreased. Ca2+-repletion also decreased protein content for AC and -AR kinase but augmented the changes in Gs- and Gi-protein functions. Although low Na+- medium perfusion during Ca2+-depletion prevented the changes in G-proteins during both Ca2+-depletion and Ca2+-repletion periods, the increased 1-AR affinity and density as well as changes in AC activities due to Ca2+-depletion were not affected while alterations due to Ca2+-repletion were fully prevented. These results suggest that changes in Ca2+-homeostasis may represent a mechanism for alterations in the -adrenergic signal transduction pathway in the heart under pathological conditions. 相似文献
4.
Although in vitro studies have shown that oxygen free radicals depress the sarcolemmal Ca2+-pump activity and thereby may cause the occurrence of intracellular Ca2+ overload for the genesis of contractile failure, the exact relationship between changes in sarcolemmal Ca2+-pump activity and cardiac function due to these radicals is not clear. In this study we examined the effects of oxygen radicals on sarcolemmal Ca2+ uptake and Ca2+-stimulated ATPase activities as well as contractile force development by employing isolated rat heart preparations. When hearts were perfused with medium containing xanthine plus xanthine oxidase, the sarcolemmal Ca2+-stimulated ATPase activity and ATP-dependent Ca2+ accumulation were depressed within 1 min whereas the developed contractile force, rate of contraction and rate of relaxation were increased at 1 min and decreased over 3–20 min of perfusion. The resting tension started increasing at 2 min of perfusion with xanthine plus xanthine oxidase. Catalase showed protective effects against these alterations in heart function and sarcolemmal Ca2+-pump activities upon perfusion with xanthine plus xanthine oxidase whereas superoxide dismutase did not exert such effects. The combination of catalase and superoxide dismutase did not produce greater effects in comparison to catalase alone. These results are consistent with the view that the depression of heart sarcolemmal Ca2+ pump activities may result in myocardial dysfunction due to the formation of hydrogen peroxide and/or hydroxyl radicals upon perfusing the hearts with xanthine plus xanthine oxidase. 相似文献
5.
Effects of sustained low-flow ischemia and reperfusion on Ca2+ transients and contractility in perfused rat hearts 总被引:1,自引:0,他引:1
Seki S Horikoshi K Takeda H Izumi T Nagata A Okumura H Taniguchi M Mochizuki S 《Molecular and cellular biochemistry》2001,216(1-2):111-119
We investigated changes in cytoplasmic Ca2+ concentration ([Ca2+]i) and in left ventricular contractility during sustained ischemia and reperfusion in isolated beating rat hearts. Hearts from male Sprague-Dawley rats were perfused retrogradely and were loaded with 4 M fura-2. Low-flow global ischemia was induced by reducing perfusion flow to 10% and by electric pacing. The hearts were exposed to ischemia for 10 min or 30 min and then reperfused. [Ca2+]i was measured by monitoring the ratio of 500 nm fluorescence excited at 340 and 380 nm while simultaneously measuring left ventricular pressure (LVP). To determine diastolic [Ca2+]i, background autofluorescence was subtracted. LVP rapidly decreased from 82.3 ± 8.2 to 17.1 ± 2.9 mmHg , whereas the amplitude of the Ca2+ transient did not change significantly during the first 1 min of ischemia. After 10 min of ischemia, the amplitude decreased to 60.8 ± 10.6% (p < 0.05) and diastolic [Ca2+]i increased by 26.3 ± 2.9% (p < 0.001) compared with the pre-ischemic value (n = 8). When the hearts were reperfused after 10 min of ischemia, the amplitude of the Ca2+ transient and LVP recovered to 79.0 ± 7.2% and 73.2 ± 7.5 mmHg, respectively. Whereas diastolic [Ca2+]i decreased to the pre-ischemic value. In the hearts exposed to 30 min of ischemia (n = 10), diastolic [Ca2+]i increased even further by 32.7 ± 5.3% at the end of ischemia and continued increasing during the 10 min of reperfusion by 42.6 ± 15.6%. Six of 10 hearts developed ventricular fibrillation (VF) and intracellular Ca2+ overload after reperfusion. Recovery of LVP after reperfusion was significantly smaller in the hearts exposed to 30 min of ischemia than in the hearts exposed to 10 min of ischemia (58.9 ± 11.7 vs. 97.2 ± 3.0% of pre-ischemic value, p < 0.05). Diastolic [Ca2+]i also increased under hypoxic conditions (N2 bubbling) in this model. These results suggest that increases in diastolic [Ca2+]i might play an important role in myocardial contractile dysfunction and viability in ischemia-reperfusion injury. 相似文献
6.
Taku Matsubara Sorin Musat-Marcu Hara P. Misra Naranjan S. Dhalla 《Molecular and cellular biochemistry》1995,153(1-2):79-85
In order to examine the mechanisms of the beneficial effects of vanadate on cardiac dysfunction in chronic diabetes, rat hearts were perfused with xanthine plus xanthine oxidase, an oxyradical generating system in the absence or presence of vanadate. The heart failed to generate contractile force and increased the resting tension markedly within 5 min of perfusion with xanthine plus xanthine oxidase. These changes were prevented by the addition of 4 M vanadate in the perfusion medium. The protective effects of vanadate on the loss of developed tension and increased resting tension due to xanthine plus xanthine oxidase were dose-dependent (0.1–5 M). Perfusion of the hearts with glucose-free medium did not abolish the protective actions of vanadate. The sarcolemmal Ca2+-pump (ATP-dependent Ca2+ uptake and Ca2+-stimulated ATPase) and Na+-dependent Ca2+ uptake activities were decreased upon perfusing the hearts with a medium containing xanthine plus xanthine oxidase for 5 min; these effects were prevented by the addition of 2–4 M vanadate in the perfusion medium. The signals for superoxide radicals produced by xanthine plus xanthine oxidase, as detected by electron paramagnetic resonance spectroscopic technique, were inhibited by 5–100 M vanadate. These results suggest that vanadate is an oxyradical scavenger and thus may prevent heart dysfunction under some pathological conditions by its antioxidant action. 相似文献
7.
L-type Ca2+ channel activity was assayed in L6 cells as the rate of nifedipine-sensitive Ba2+ influx in a depolarizing medium. In the absence of extracellular Ca2+, activation of protein kinase C (PKC) with phorbol-12-myristate-13-acetate (PMA) or thymeleatoxin (TMX) inhibited Ba2+ influx by 38%. Thapsigargin (Tg), a selective inhibitor of the Ca2+-ATPase in the sarcoplasmic reticulum, evoked a rise in the cytosolic Ca2+ concentration ([Ca2+]i) in a Ca2+-free medium from 30 to 80 nM. This [Ca2+]i increase declined slowly, giving rise to a modest elevation of [Ca2+]i that persisted for >5 min. The inhibitory effects of PMA and TMX on channel activity were abolished when tested in Tg-treated cells in a Ca2+-free medium. However, when the Ca2+ ionophore, ionomycin, was applied with Tg, PMA and TMX retained their inhibitory effect on L-type Ca2+ channel activity, suggesting that a lower amplitude and prolonged release of Ca2+ stores is necessary for abrogating PKC-mediated inhibition of LCC. Cyclosporin A (5 μM) and ascomycin (5 μM), inhibitors of the Ca2+/calmodulin-dependent protein phosphatase, calcineurin, fully restored the inhibitory effect of PMA and TMX on channel activity. Addition of 1 mM CaCl2 to the Tg-treated cells increased [Ca2+]i to 165 nM and also restored the inhibitory effects of PMA and TMX. These results indicate that a small, relatively prolonged [Ca2+]i increase elicited by passive depletion of internal Ca2+ stores led to activation of calcineurin, giving rise to an increase in protein phosphatase activity that counteracted the inhibitory effects of PKC on channel activity. A larger increase in [Ca2+]i via store-dependent Ca2+ entry enhanced the activity of PKC sufficiently to overcome the protein phosphatase activity of calcineurin. This study is the first to demonstrate that the regulation of L-type Ca2+ channels in a myocyte model involves a balance between the differential Ca2+ sensitivities and opposing actions of PKC and calcineurin. 相似文献
8.
Extracellular ATP caused a dose-dependent accumulation of inositol phosphates and a rise in cytosolic free Ca2+ ([Ca2+]i) in C6 glioma cells with an EC50 of 60±4 and 10±5 M, respectively. The threshold concentration of ATP (3 M) for increasing [Ca2+]i was approximately 10-fold less than that for stimulating phosphoinositide (PI) turnover. The PI response showed a preference for ATP; ADP was about 3-fold less potent than ATP but had a comparable maximal stimulation (11-fold of the control). AMP and adenosine were without effect at concentrations up to 1 mM. ATP-stimulated PI metabolism was found to be partially dependent on extracellular Ca2+ and Na+ but was resistant to tetrodotoxin, saxitoxin, amiloride, ouabain, and inorganic blockers of Ca2+ channels (Co2+, Mn2+, La3+, or Cd2+). In Ca2+-free medium, ATP caused only a transient increase in [Ca2+]i as opposed to a sustained [Ca2+]i increase in normal medium. The ATP-induced elevation of [Ca2+]i was resistant to Na+ depletion and treatment with saxitoxin, verapamil and nisoldipine, but was attentuated by La3+. The differences in the characteristics of ATP-caused P1 hydrolysis and [Ca2+]i rise suggest that ATP receptors are independently coupled to phospholipase C and receptor-gated Ca2+ channels. Because of the robust effect of ATP in stimulating PI turnover and the apparent absence of P1-purinergic receptors, the C6 glioma cell line provides a useful model for investigating the transmembrane signalling pathway induced by extracellular ATP. The mechanisms underlying the unexpected finding of [Na+]o dependency for ATP-induced PI turnover require further investigation.Abbreviations PI
phosphoinositide
- [Ca2+]i
cytosolic free Ca2+ concentration
- PDBu
phorbol 12, 13-dibutyrate
- PSS
physiological saline solution
- IP
inositol phosphates
- IP1
inositol monophosphate
- IP2
inositol bisphosphate
- IP3
inositol trisphosphate
- IP4
inositol (1,3,4,5) tetrakisphosphate
- PLC
phospholipase C 相似文献
9.
Takeo S Nasa Y Tanonaka K Yamaguchi F Yabe K Hayashi H Dhalla NS 《Molecular and cellular biochemistry》2000,212(1-2):227-235
The aim of this study was to explore the possible participation of cardiac renin-angiotensin system (RAS) in the ischemia-reperfusion induced changes in heart function as well as Ca2+-handling activities and gene expression of cardiac sarcoplasmic reticulum (SR) proteins. The isolated rat hearts, treated for 10 min without and with 30 M captopril or 100 M losartan, were subjected to 30 min ischemia followed by reperfusion for 60 min and processed for the measurement of SR function and gene expression. Attenuated recovery of the left ventricular developed pressure (LVDP) upon reperfusion of the ischemic heart was accompanied by a marked reduction in SR Ca2+-pump ATPase, Ca2+-uptake and Ca2+-release activities. Northern blot analysis revealed that mRNA levels for SR Ca2+-handling proteins such as Ca2+-pump ATPase (SERCA2a), ryanodine receptor, calsequestrin and phospholamban were decreased in the ischemia-reperfused heart as compared with the non-ischemic control. Treatment with captopril improved the recovery of LVDP as well as SR Ca2+-pump ATPase and Ca2+-uptake activities in the postischemic hearts but had no effect on changes in Ca2+-release activity due to ischemic-reperfusion. Losartan neither affected the changes in contractile function nor modified alterations in SR Ca2+-handling activities. The ischemia-reperfusion induced decrease in mRNA levels for SR Ca2+-handling proteins were not affected by treatment with captopril or losartan. The results suggest that the improvement of cardiac function in the ischemic-reperfused heart by captopril is associated with the preservation of SR Ca2+-pump activities; however, it is unlikely that this action of captopril is mediated through the modification of cardiac RAS. Furthermore, cardiac RAS does not appear to contribute towards the ischemia-reperfusion induced changes in gene expression for SR Ca2+-handling proteins. 相似文献
10.
Importance of Ca2+ influx by Na+/Ca2+ exchange under normal and sodium-loaded conditions in mammalian ventricles 总被引:2,自引:0,他引:2
Satoh H Mukai M Urushida T Katoh H Terada H Hayashi H 《Molecular and cellular biochemistry》2003,242(1-2):11-17
Na+/Ca2+ exchange (NCX) is a major Ca2+ extrusion system in cardiac myocytes, but can also mediate Ca2+ influx and trigger sarcoplasmic reticulum Ca2+ release. Under conditions such as digitalis toxicity or ischemia/reperfusion, increased [Na+]i may lead to a rise in [Ca2+]i through NCX, causing Ca2+ overload and triggered arrhythmias. Here we used an agent which selectively blocks Ca2+ influx by NCX, KB-R7943 (KBR), and assessed twitch contractions and Ca2+ transients in rat and guinea pig ventricular myocytes loaded with indo-1. KBR (5 M) did not alter control steady-state twitch contractions or Ca2+ transients at 0.5 Hz in rat, but significantly decreased them in guinea pig myocytes. When cells were Na+-loaded by perfusion of strophanthidin (50 M), the addition of KBR reduced diastolic [Ca2+]i and abolished spontaneous Ca2+ oscillations. In guinea pig papillary muscles exposed to substrate-free hypoxic medium for 60 min, KBR (10 M applied 10 min before and during reoxygenation) reduced both the incidence and duration of reoxygenation-induced arrhythmias. KBR also enhanced the recovery of developed tension after reoxygenation. It is concluded that (1) the importance of Ca2+ influx via NCX for normal excitation-contraction coupling is species-dependent, and (2) Ca2+ influx via NCX may be critical in causing myocardial Ca2+ overload and triggered activities induced by cardiac glycoside or reoxygenation. 相似文献
11.
Summary Two-dimensional crystalline arrays of Ca2+-ATPase molecules develop after treatment of sarcoplasmic reticulum vesicles with Na3VO4 in a Ca2+-free medium. The influence of membrane potential upon the rate of crystallization was studied by ion substitution using oxonol VI and 3,3-diethyl-2,2-thiadicarbocyanine (Di–S–C2(5)) to monitor inside positive or inside negative membrane, potentials, respectively. Positive transmembrane potential accelerates the rate of crystallization of Ca2+-ATPase, while negative potential disrupts preformed Ca2+-ATPase crystals, suggesting an influence of transmembrane potential upon the conformation of Ca2+-ATPase. 相似文献
12.
Jansen MA Badlou BA van Echteld CJ Ruigrok TJ 《Molecular and cellular biochemistry》2000,203(1-2):169-175
Reperfusion of isolated mammalian hearts with a Ca2+-containing solution after a short Ca2+-free period at 37°:C results in massive influx of Ca2+ into the cells and irreversible cell damage: the Ca2+paradox. Information about the free intracellular, cytosolic [Ca2+] ([Ca2+]i) during Ca2+ depletion is essential to assess the possibility of Ca2+ influx through reversed Na+/Ca2+ exchange upon Ca2+ repletion. Furthermore, the increase in end-diastolic pressure often seen during Ca2+-free perfusion of intact hearts may be similar to that seen during ischemia and caused by liberation of Ca2+ from intracellular stores. Therefore, in this study, we measured [Ca2+]i during Ca2+- free perfusion of isolated rat hearts. To this end, the fluorescent indicator Indo-1 was loaded into isolated Langendorff-perfused hearts and Ca2+-transients were recorded. Ca2+-transients disappeared within 1 min of Ca2+ depletion. Systolic [Ca2+]i during control perfusion was 268±54 nM. Diastolic [Ca2+]i during control perfusion was 114±34 nM and decreased to 53±19 nM after 10 min of Ca2+ depletion. Left ventricular end-diastolic pressure (LVEDP) significantly increased from 13±4 mmHg during control perfusion after Indo-1 AM loading to 31±5 mmHg after 10 min Ca2+ depletion. Left ventricular developed pressure did not recover during Ca2+ repletion, indicating a full Ca2+ paradox. These results show that LVEDP increased during Ca2+ depletion despite a decrease in [Ca2+]i, and is therefore not comparable to the contracture seen during ischemia. Furthermore, calculation of the driving force for the Na+/Ca2+ exchanger showed that reversed Na+/Ca2+ exchange during Ca2+ repletion is not able to increase [Ca2+]i to cytotoxic levels. 相似文献
13.
Ian M. C. Dixon Masanori Kaneko Tomoji Hata Vincenzo Panagia Naranjan S. Dhalla 《Molecular and cellular biochemistry》1990,99(2):125-133
Although cardiac dysfunction due to ischemia-reperfusion injury is considered to involve oxygen free radicals, the exact manner by which this oxidative stress affects the myocardium is not clear. As the occurrence of intracellular Ca2+ overload has been shown to play a critical role in the genesis of cellular damage due to ischemia-reperfusion, this study was undertaken to examine whether oxygen free radicals are involved in altering the sarcolemmal Ca2+-transport activities due to reperfusion injury. When isolated rat hearts were made globally ischemic for 30 min and then reperfused for 5 min, the Ca2+ -pump and Na+-Ca2+ exchange activities were depressed in the purified sarcolemmal fraction; these alterations were prevented when a free radical scavenger enzymes (superoxide dismutase plus catalase) were added to the reperfusion medium. Both the Ca2+- pump and Na+- Ca2+ exchange activities in control heart sarcolemmal preparations were depressed by activated oxygen-generating systems containing xanthine plus xanthine oxidase and H2O2; these changes were prevented by the inclusion of superoxide dismutase and catalase in the incubation medium. These results support the view that oxidative stress during ischemia-reperfusion may contribute towards the occurrence of intracellular Ca2+ overload and subsequent cell damage by depressing the sarcolemmal mechanisms governing the efflux of Ca2+ from the cardiac cell. 相似文献
14.
The involvement of different subtypes of voltage-sensitive Ca2+ channels in the initiation of field stimulation-induced endogenous adenosine triphosphate (ATP) and [3H]acetylcholine ([3H]ACh) release was investigated in the superfused rat habenula slices. ATP, measured by the luciferin-luciferase assay, and [3H]ACh were released simultaneously from the tissue in response to low frequency electrical stimulation (2 Hz, 2.5 msec, 360 shocks). The N-type Ca2+ channel blocker -conotoxin GVIA (-CgTX, 0.01–1 M) reduced the stimulation-evoked release of ATP and [3H]ACh in a dose-dependent manner. Similarly, the P-type Ca2+ channel antagonist -agatoxin IVA (-Aga IVA) (0.05 M) and the inorganic Ca2+ channel blocker Cd2+ (0.2 mM) inhibited the outflow of both transmitters, while Ni2+ (0.1 mM) was without significant effect. A high correlation was observed between the percent inhibition of ATP release and percent inhibition of ACh release caused by the different Ca2+ antagonists. Long-term perfusion (i.e., 90 min) with Ca2+ free solution inhibited the evoked-release of ATP and [3H]ACh. In contrast, perfusion of slices with the same media for a shorter time (i.e., 20 min) did not reduce the release of [3H]ACh and ATP but even increased the evoked-release of ATP about fourfold. The breakdown of extracellular ATP was not blocked under low [Ca2+]0 condition, measured by the creatine phosphokinase assay and HPLC-UV technique. Application of extra- or intracellular Ca2+ chelators, and dipyridamole (2 M), the nucleoside transporter inhibitor, did not reduce the excess release of ATP after short-term perfusion with Ca2+-free media. Tetrodotoxin (TTX, 1 M), while inhibiting the majority of ATP release under normal conditions, was also unable to reduce release under low [Ca2+]0 conditions. In summary, we showed that both N- and P-type Ca2+ channels are involved in the initiation of electrical stimulation-evoked release of ATP and [3H]ACh in the rat habenula under normal extracellular calcium concentration. Under low [Ca2+]0 conditions an additional release of ATP occurs, which is not associated with action potential propagation. 相似文献
15.
These experiments were designed to learn the role of bradykinin induced changes in intracellular Ca2+ in the activation of phospholipase D activity in PC12 cells. Ionomycin at a concentration of 0.1M caused an increase in intracellular Ca2+ comparable to bradykinin, but had no effect on phospholipase D activity. Carbachol, ATP, and thapsigargin also increased intracellular Ca2+ but had no effect on phospholipase D activity. Increases in intracellular Ca2+ may be a necessary but not a sufficient factor in the activation of phospholipase D. To investigate this issue, the bradykinin induced increase in intracellular Ca2+ was blocked by preincubating the cells in Ca2+-free media plus EGTA or in media containing the intracellular Ca2+ chelator BAPTA/AM. These preincubations completely blocked the bradykinin induced increase in intracellular Ca2+ but only attenuated the bradykinin mediated activation of phospholipase D. Physiological increases in intracellular Ca2+ apparently do not mediate the effect of bradykinin on phospholipase D. 相似文献
16.
Oscillations of cytosolic Ca2+ activity ([Ca2+]i) induced by stimulation with ATP in rat astrocytes in primary cultures were analysed. Astrocytes, prepared from the brains of newborn rats, loaded with the fluorescent Ca2+ indicator fura-2/AM, were continuously stimulated with ATP (10 M). ATP caused a large initial [Ca2+ peak, followed by regular [Ca2+]i oscillations (frequencies 1–5/min). Astrocytes were identified by glial fibrillary acidic protein staining of cells after [Ca2+]i recording. The oscillations were reversibly blocked by the P2 purinoceptor antagonist suramin (30 M). Influx of extracellular Ca2+ and mobilization of Ca2+ from intracellular stores both contributed to the oscillations. The effects of hypertonic and hypotonic superfusion medium on ATP-induced [Ca2+]i oscillations were examined. Hypertonic medium (430 mOsm) reversibly suppressed the ATP-induced oscillations. Hypotonic medium (250 mOsm), in spite of having heterogeneous effects, most frequently induced a rise in [Ca2+]i, or reversibly increased the frequency of the oscillations. Thus, a change in cell volume might be closely connected with [Ca2+]i oscillations in astrocytes indicating that [Ca2+]i oscillations in glial cells play an important role in regulatory volume regulation in the brain. 相似文献
17.
Divalent cation (Mn2+, Ca2+) entry into rat parotid acinar cells is stimulated by the release of Ca2+ from the internal agonist-sensitive Ca2+ pool via a mechanism which is not yet defined. This study examines the effect of temperature on Mn2+ influx into internal Ca2+ pool-depleted acini (depl-acini, as a result of carbachol stimulation of acini in a Ca2+-free medium for 10 min) and passive 45Ca2+ influx in basolateral membrane vesicles (BLMV). Mn2+ entry into deplacini was decreased when the incubation temperature was lowered from 37 to 4°C. At 4°C, Mn2+ entry appeared to be inactivated since it was not increased by raising extracellular [Mn2+] from 50 m up to 1 mm. The Arrhenius plot of depletion-activated Mn2+ entry between 37 and 8°C was nonlinear, with a change in the slope at about 21°C. The activation energy (Ea) increased from 10 kcal/mol (Q10=1.7) at 21–37°C to 25 kcal/mol (Q10=3.0) at 21-8°C. Under the same conditions, Mn2+ entry into basal (unstimulated) cells and ionomycin (5 m) permeabilized depl-acini exhibit a linear decrease, with E
a
of 7.8 kcal/mol (Q10=1.5) and 6.2 kcal/mol (Q10 < 1.5), respectively. These data suggest that depletion-activated Mn2+ entry into parotid acini is regulated by a mechanism which is strongly temperature dependent and distinct from Mn2+ entry into unstimulated acini.As in intact acini, Ca2+ influx into BLMV was decreased (by 40%) when the temperature of the reaction medium was lowered from 37 to 4°C. Kinetic analysis of the initial rates of Ca2+ influx in BLMV at 37°C demonstrated the presence of two Ca2+ influx components: a saturable component, with K
Ca
=279 ± 43 m, Vmax = 3.38 ± 0.4 nmol Ca2+/mg protein/min, and an apparently unsaturable component. At 4°C, there was no significant change in the affinity of the saturable component, but Vmax decreased by 61% to 1.3 ± 0.4 nmol Ca2+/mg protein/min. There was no detectable change in the unsaturable component. When BLMV were treated with DCCD (5 mm) or trypsin (1100, enzyme to membrane) for 30 min at 37°C there was a 40% decrease in Ca2+ influx. When BLMV were treated with DCCD or trypsin at 4°C and subsequently assayed for Ca2+ uptake at 37°C there was no significant loss of Ca2+ influx. These data suggest that the temperature sensitive high affinity Ca2+ flux component in BLMV is mediated by a protein which undergoes a modification at low temperatures, resulting in decreased Ca2+ transport.We thank Dr. Bruce Baum, Dr. Yukiharu Hiramatsu, Dr. Ofer Eidelman, and our other colleagues for their support during this work. 相似文献
18.
Lack of both oxygen and glucose contributes to I/R-induced changes in cardiac SR function 总被引:1,自引:0,他引:1
Temsah RM Netticadan T Kawabata K Dhalla NS 《American journal of physiology. Cell physiology》2002,283(4):C1306-C1312
Although ischemia-reperfusion(I/R) has been shown to depress cardiac performance and sarcoplasmicreticulum (SR) function, the mechanisms underlying these alterationsare poorly understood. Because lack of oxygen and substrate deprivationare known to occur during the ischemic phase, we examined theeffects of reperfusion on cardiac performance and SR function in heartssubjected to hypoxia and substrate lack. For this purpose, isolated rathearts were perfused with hypoxic and/or glucose-free medium for 30 min and then reperfused with normal medium for 1 h; the SR vesicles were isolated for studying the Ca2+-transport activities.Reperfusion with normal medium of hearts deprived of oxygen or glucoseshowed no changes in cardiac performance and SR function. However,reperfusion of hearts perfused with hypoxic glucose-free medium showed~45% decrease in cardiac contractile activities as well as 23 and64% reduction in SR Ca2+-uptake andCa2+-release activities, respectively, without any changein the level of SR Ca2+-cycling proteins. Depressed SRfunction in these hearts was associated with a reduction inCa2+/calmodulin-dependent protein kinase (CaMK)phosphorylation of the SR Ca2+-cycling proteins and 34%decrease in SR CaMK activity. These changes in cardiac performance, SRfunction, and SR CaMK activity in the hypoxic, glucose-deprived,reperfused hearts were similar to those observed in hearts subjected to30 min of global ischemia and 60 min of reperfusion. Theresults therefore suggest that the lack of both oxygen and substrateduring the ischemic phase may contribute to the I/R-inducedalterations in cardiac performance and SR function. Furthermore, theseabnormalities were associated with reduced SR CaMK activity. 相似文献
19.
The effects of glutamate agonists and their selective antagonists on the Ca2+-dependent and independent releases of [3H]GABA from rat coronal hippocampal slices were studied in a superfusion system. The Ca2+-dependent release evoked by glutamate, kainate and N-methyl-D-aspartate (NMDA) gradually declined with time despite the continuous presence of the agonists. Quisqualate (QA) caused a sustained release which exhibited no tendency to decline within the 20-min period of stimulation. This release was enhanced in Ca2+-free medium. The release evoked by QA in Ca2+-containing medium was significantly inhibited by (+)-5-methyl-10,11-dihydro-5H-dibenzo(a,d)cyclohept-5,10-imine hydrogen maleate (MK-801) and 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), showing that QA activates NMDA receptors directly or indirectly through (RS)--amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) receptors. The inhibition of MK-801 was slightly diminished and that of CNQX totally abolished in Ca2+-free medium. Verapamil inhibited the QA-activated release in both Ca2+-containing and Ca2+-free media. The effect of QA but not that of AMPA was blocked in Ca2+-free medium by L(+)-2-amino-3-phosphonopropionate (L-AP3), a selective antagonist of the metabotropic glutamate receptor. It is suggested that the sustained release of GABA is also mediated partly by activation of metabotropic receptors and mobilization of Ca2+ from intracellular stores. 相似文献
20.
The contribution of the cryoprotectant to total injury in rabbit hearts frozen with ethylene glycol.
Following the failure of hearts to recover function after freezing at ?20 ° in the presence of 3 m ethylene glycol, a variety of experimental treatments was devised to determine the relative harmfulness of ice, high concentrations of electrolytes and high ethylene glycol concentration. Neither cooling to ?20 °C without freezing in a Ca2+-free solution containing twice the normal salt concentration and 6 m ethylene glycol (freezing 3 m ethylene glycol at ?20 °C doubles the solute concentration in the liquid phase), nor perfusion at ?1 °C with this solution were conducive to the recovery of hearts. However, perfusion with Ca2+-free 3 m ethylene glycol solution with twice the normal concentration of salts did allow full recovery of function, whereas perfusion with Ca2+-free 6 m ethylene glycol solution with normal salt concentrations did not. Therefore, the high ethylene glycol concentration encountered during freezing was the main cause of damage. 相似文献