Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.6.1.3 (ATPase)
 65,361 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

1. The effect of drugs affecting calcium and potassium channels and intracellular calcium handling/release on electromechanical coupling in the smooth muscle of the guinea-pig proximal vs. distal renal pelvis were investigated by using the single sucrose gap method. 2. Spontaneous action potentials discharged from the proximal renal pelvis were bell-shaped, did not show a pronounced plateau and had a small after-hyperpolarization. Spontaneous action potentials from the distal renal pelvis were characterized by a fast depolarization, a pronounced plateau and after-hyperpolarization. 3. Nifedipine (1 microM) suppressed action potentials in both regions of the renal pelvis. A submaximally effective concentration of nifedipine (50 nM) shortened action potential duration and reduced contractility in both regions of the renal pelvis. On the other hand Bay K 8644 (1 microM) markedly prolonged the duration of the action potential and increased contractility in both regions of the renal pelvis. 4. Tetraethylammonium (0.5 mM) markedly prolonged the action potential duration and contraction in the distal renal pelvis without affecting action potentials in the proximal renal pelvis. Similar effects were produced by a slightly higher concentration of tetraethylammonium (2 mM) in the proximal renal pelvis. 5. Charybdotoxin (30 nM) markedly prolonged the duration of action potential and increased and prolonged the contraction in both the proximal and distal renal pelvis. 6. 4-aminopyridine (1 mM) selectively increased the frequency of action potentials in the distal renal pelvis without affecting other parameters of the action potential nor contractility. 4-aminopyridine had no effect in the proximal renal pelvis. 7. The inhibitor of sarcoplasmic reticulum Ca-ATPase, cyclopiazonic acid (10 microM) transiently increased the frequency of action potentials in both regions of the renal pelvis; CPA markedly delayed the repolarizing phase of the action potential in both the proximal and distal renal pelvis and, in parallel, increased contractility. 8. We conclude that action potentials generated from the proximal and distal regions of the guinea-pig renal pelvis are evenly dependent upon the availability of L-type Ca channels; that Ca-dependent maxi K channels provide a major contribution to the repolarization of action potentials in both regions of the renal pelvis, thus regulating duration/intensity of Ca influx and contraction; that release of Ca from the internal store is not important in providing activator Ca for contraction but regulates duration of the action potential and may be involved in setting the frequency of discharge of pacemaker cells.
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PMID:Pharmacological modulation of electromechanical coupling in the proximal and distal regions of the guinea-pig renal pelvis. 920 59

In canine airway smooth muscle, cyclopiazonic acid (CPA; selective blocker of the sarcoplasmic reticulum Ca(2+)-pump) evokes a contractile response which is initially mediated via release of internally sequestered Ca2+, but is later supported almost exclusively by electromechanical coupling. As such, this second component is highly sensitive to inhibition of voltage-dependent Ca(2+)-influx (e.g. dihydropyridines, removal of external Ca2+) or to membrane hyperpolarization. In the present study, we describe relaxations which occur spontaneously during this second component of the CPA-evoked contraction. These relaxations are also electromechanically mediated, since they are abolished by depolarization of the membrane by high-K+ media. TEA has relatively little effect on the phasic activity, thus ruling out an involvement of Ca(2+)-dependent K+ channels. On the other hand, the phasic activity is abolished by ouabain, by removal of external K+, or by cooling and is markedly slowed by removal of external Na+. These observations indicate that the phasic activity is mediated by the Na+/K(+)-ATPase.
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PMID:Na+/K+ ATPase mediates rhythmic spontaneous relaxations in canine airway smooth muscle. 923 92

1. Inhalation of vanadium compounds, particularly vanadate, is a cause of occupational bronchial asthma. We have now studied the action of vanadate on human isolated bronchus. Vanadate (0.1 microM-3 mM) produced concentration-dependent, well-sustained contraction. Its -logEC50 was 3.74 +/- 0.05 (mean +/- s.e.mean) and its maximal effect was equivalent to 97.5 +/- 4.2% of the response to acetylcholine (ACh, 1 mM). 2. Vanadate (200 microM)-induced contraction of human bronchus was epithelium-independent and was not inhibited by indomethacin (2.8 microM), zileuton (10 microM), a mixture of atropine, mepyramine and phentolamine (each at 1 microM), or by mast cell degranulation with compound 48/80. 3. Vanadate (200 microM)-induced contraction was unaltered by tissue exposure to verapamil or nifedipine (each 1 microM) or to a Ca2+-free, EGTA (0.1 mM)-containing physiological salt solution (PSS). However, tissue incubation with ryanodine (10 microM) in Ca2+-free, EGTA (0.1 mM)-containing PSS reduced vanadate-induced contraction. A series of vanadate challenges was made in tissues exposed to Ca2+-free EGTA (0.1 mM)-containing PSS with the object of depleting intracellular Ca2+ stores. In such tissues cyclopiazonic acid (CPA; 10 microM) prevented Ca2+-induced recovery of vanadate-induced contraction. 4. Tissue incubation in K+-rich (80 mM) PSS, K+-free PSS, or PSS containing ouabain (10 microM) did not alter vanadate (200 microM)-induced contraction. Ouabain (10 microM) abolished the K+-induced relaxation of human bronchus bathed in K+-free PSS. This action was not shared by vanadate (200 microM). The tissue content of Na+ was increased and the tissue content of K+ was decreased by ouabain (10 microM). In contrast, vanadate (200 microM) did not alter the tissue content of these ions. Tissue incubation in a Na+-deficient (25 mM) PSS or in PSS containing amiloride (0.1 mM) markedly inhibited the spasmogenic effect of vanadate (200 microM). 5. Vanadate (200 microM)-induced contractions were markedly reduced by tissue treatment with each of the protein kinase C (PKC) inhibitors H-7 (10 microM), staurosporine (1 microM) and calphostin C (1 microM). Genistein (100 microM), an inhibitor of protein tyrosine kinase, also reduced the response to vanadate. 6 Vanadate (0.1-3 mM) and ACh (1 microM- 3 mM) each increased inositol phosphate accumulation in bronchus. Such responses were unaffected by a Ca2+-free medium either alone or in combination with ryanodine (10 microM). 7. In human cultured tracheal smooth muscle cells, histamine (100 microM) and vanadate (200 microM) each produced a transient increase in intracellular Ca2+ concentration ([Ca2+]i). 8. Intracellular microelectrode recording showed that the contractile effect of vanadate (200 microM) in human bronchus was associated with cellular depolarization. 9. It is concluded that vanadate acts directly on human bronchial smooth muscle, promoting the release of Ca2+ from an intracellular store. The Ca2+ release mechanism involves both the production of inositol phosphate second messengers and inhibition of Ca-ATPase. The activation of PKC plays an important role in mediating vanadate-induced contraction at values of [Ca2+]i that are close to basal.
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PMID:The spasmogenic effects of vanadate in human isolated bronchus. 925 12

1. We have used a cascade bioassay system and isolated arterial ring preparations to investigate the contribution of Ca2+ release from endothelial intracellular stores to nitric oxide (NO) production evoked by increases in shear stress and by acetylcholine in rabbit aorta. 2. Experiments were performed before and following incubation with either the endoplasmic reticulum Ca(2+)-ATPase inhibitors cyclopiazonic acid (CPA, 10 microM) and thapsigargin (TSG, 1 microM) or ryanodine (30, 100 microM) which binds to a specific endoplasmic reticulum Ca(2+)-release channel. 3. In cascade bioassay all three agents induced relaxations of the recipient ring (CPA, 24.4 +/- 3.8%; TSG, 51.5 +/- 10.6%; ryanodine, 17.4 +/- 1.6%) which were significantly attenuated by preincubation of the donor with 100 microM NG-nitro-L-arginine methyl ester (L-NAME). However, in isolated rings, only CPA and TSG induced L-NAME-sensitive relaxations (CPA 52.7 +/- 6.5%; TSG 61.3 +/- 7%). 4. Addition of superoxide dismutase (SOD) to the donor perfusate evoked relaxations of the recipient ring in cascade bioassay (13.3 +/- 1.4%, n = 22). Prior administration of SOD attenuated relaxations to TSG (23.2 +/- 3.8% n = 4) and ryanodine (1.7 +/- 0.8%, n = 4), and pre-incubation with TSG and ryanodine blunted SOD-induced responses (4 +/- 1.5%, n = 4 and 8.9 +/- 1.1%, n = 4, respectively). By contrast, no interaction was observed between the relaxations evoked by SOD and CPA. In isolated rings, SOD exerted no direct relaxant and did not modulate relaxations to CPA, TSG or ryanodine. 5. In cascade bioassay studies time-averaged shear stress was manipulated with dextran (1-4% w/v, 800000 MW) to increase perfusate viscosity. NO-dependent relaxation of the recipient ring induced by increased perfusate viscosity was significantly attenuated by CPA (P < 0.01; n = 6) and TSG (P < 0.05; n = 7), but not by ryanodine (n = 6). 6. Endothelium-dependent relaxations to acetylcholine (0.1-30 microM) in cascade bioassay and in isolated aortic ring preparations were markedly attenuated by pretreatment with CPA and TSG, but were unaffected by ryanodine. Ryanodine and CPA caused only a small attenuation of endothelium-independent relaxations to sodium nitroprusside (0.001-10 microM), whereas TSG had no effect. 7. We conclude that release of Ca2+ from CPA- and TSG-sensitive endothelial stores is necessary for NO release evoked by acute flow changes and agonists in rabbit abdominal aorta. Ca(2+)-induced Ca2+ release via the ryanodine-sensitive release channel plays no direct role in these responses. Free radical interactions may complicate the interpretation of findings in cascade bioassay compared with isolated ring preparations.
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PMID:Central role of intracellular calcium stores in acute flow- and agonist-evoked endothelial nitric oxide release. 929 37

The present study investigated the functional role of the sarcoplasmic reticulum Ca++-ATPase in contraction and relaxation, intracellular Ca++-transients, as well as on the force-frequency relationship in human myocardium. The Ca++-ATPase activity of membrane vesicles isolated from sarcoplasmic reticulum (SR) obtained from nonfailing donor hearts (n = 7) was measured in the presence of cyclopiazonic acid (CPA, 0-30 microM), a highly specific inhibitor of the Ca++-ATPase of the SR (SERCA). The effects of CPA on parameters of contraction and relaxation, force-frequency relationship and [Ca++]i transients (with fura-2) were studied on isolated left ventricular muscle strips from human nonfailing myocardium. CPA concentration-dependently inhibited SERCA activity of isolated SR vesicles. In the presence of CPA (30 microM) the former positive force-frequency relationship in human left ventricular nonfailing myocardium became negative. Especially at high frequencies of stimulation, CPA decreased developed tension, peak rate of tension rise and systolic fura-2-light emission, whereas time to peak tension, time to peak [Ca++]i, time to 95% relaxation, diastolic tension and diastolic Ca++ levels were increased. Peak rate of tension decay and time to half-relaxation and half-decay of [Ca++]i were not altered significantly after treatment with CPA. These findings provide evidence that the SERCA plays a functional role in the frequency-dependent increase in force of contraction in human myocardium. Because an impaired function of the SERCA is predominantly followed by alterations of inotropic and to a lesser degree of lusitropic function, other important factors to lower [Ca++]i and influence relaxation may be present in human myocardium to compensate for the reduced SERCA activity, e.g., Na+-Ca++ exchanger.
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PMID:Effect of cyclopiazonic acid on the force-frequency relationship in human nonfailing myocardium. 933 35

We have investigated the effects of glutamate and glutamate receptor ligands on the intracellular free Ca2+ concentration ([Ca2+]i) and the membrane potential (Em) of single, identified neuropile glial cells in the central nervous system of the leech Hirudo medicinalis. Exposed glial cells of isolated ganglia were filled iontophoretically with the Ca2+ indicator dye Fura-2. Application of glutamate (200-500 mumoll-1) caused biphasic membrane potential shifts and increases in [Ca2+]i, which were only partly reduced by either removing extracellular Ca2+ or blocking ionotropic glutamate receptors with 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, 50-100 mumol l-1. Metabotropic glutamate receptor (mGluR) ligands had the following rank of potency in inducing a rise in [Ca2+]i: quisqualate (QQ, 200 mumol l-1) > glutamate (200 mumol l-1) > L(+)2-amino-3-phosphonopropionic acid (L-AP3, 200 mumol l-1 > trans-1-aminocyclopentane-1,3-dicarboxylic acid (t-ACPD, 400 mumol l-1). The mGluR-selective antagonist (RS)-alpha-methyl-4-carboxyphenylglycine [(RS)-MCPG, 1 mmol l-1] significantly reduced glutamate-evoked increases in [Ca2+]i by 20%. Incubation of the ganglia with the endoplasmic ATPase inhibitor cyclopiazonic acid (CPA, 10 mumol l-1) caused a significant (53%) reduction of glutamate-induced [Ca2+]i transients, while incubation with lithium ions (2 mmol l-1) resulted in a 46% reduction. The effects of depleting the Ca2+ stores with CPA and of CNQX were additive. We conclude that glutamate-induced [Ca2+]i transients were mediated by activation of both Ca(2+)-permeable ionotropic non-NMDA receptors and of metabotropic glutamate receptors leading to Ca2+ release from intracellular Ca2+ stores.
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PMID:Intracellular Ca2+ release mediated by metabotropic glutamate receptor activation in the leech giant glial cell. 936 87

We investigated the relationship between voltage-operated Ca2+ channel current and the corresponding intracellular Ca2+ concentration ([Ca2+]i) change (Ca2+ transient) in guinea pig gastric myocytes. Fluorescence microspectroscopy was combined with conventional whole cell patch-clamp technique, and fura 2 (80 microM) was added to CsCl-rich pipette solution. Step depolarization to 0 mV induced inward Ca2+ current (ICa) and concomitantly raised [Ca2+]i. Both responses were suppressed by nicardipine, an L-type Ca2+ channel blocker, and the voltage dependence of Ca2+ transient was similar to the current-voltage relation of ICa. When pulse duration was increased by up to 900 ms, peak Ca2+ transient increased and reached a steady state when stimulation was for longer. The calculated fast Ca2+ buffering capacity (B value), determined as the ratio of the time integral of ICa divided by the amplitude of Ca2+ transient, was not significantly increased after depletion of Ca2+ stores by the cyclic application of caffeine (10 mM) in the presence of ryanodine (4 microM). The addition of cyclopiazonic acid (CPA, 10 microM), a sarco(endo)plasmic reticulum Ca(2+)-ATPase inhibitor, decreased B value by approximately 20% in a reversible manner. When KCl pipette solution was used, Ca(2+)-activated K+ current [IK(Ca)] was also recorded during step depolarization. CPA sensitively suppressed the initial peak and oscillations of IK(Ca) with irregular effects on Ca2+ transients. The above results suggest that, in guinea pig gastric myocyte, Ca2+ transient is tightly coupled to ICa during depolarization, and global [Ca2+]i is not significantly affected by Ca(2+)-induced Ca2+ release from sarcoplasmic reticulum during depolarization.
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PMID:Changes in intracellular Ca2+ concentration induced by L-type Ca2+ channel current in guinea pig gastric myocytes. 943

Results from experiments performed with permanent non-neuronal cell lines suggest that endoplasmic reticulum (ER) calcium homeostasis plays a key role in the control of protein synthesis (PS). It has been concluded that disturbances in ER calcium homeostasis may contribute to the suppression of PS triggered by a severe metabolic stress (W. Paschen, Med. Hypoth., 47 (1996) 283-288). To elucidate how an emptying of ER calcium stores of these cells would effect PS and ribosomal aggregation of non-transformed fully differentiated cells, experiments were run on primary neuronal cell cultures. ER calcium stores were depleted by treating cells with thapsigargin (TG, a selective, irreversible inhibitor of ER Ca(2+)-ATPase), cyclopiazonic acid (CPA, a reversible inhibitor of ER Ca(2+)-ATPase), or caffeine (an agonist of ER ryanodine receptor). Changes in intracellular calcium activity were evaluated by fluorescence microscopy using fura-2-loaded cells. Protein synthesis was determined by measuring the incorporation of [3H]leucine into proteins. The degree of aggregation of ribosomes was evaluated by electron microscopy. TG induced a permanent inhibition of PS to about 10% of control which was only partially reversed within 2 h of recovery. CPA caused about 70% inhibition of PS, and PS recovered completely 60 min after treatment. Caffeine produced an inhibition of PS to about 50% of control. Loading cells with the calcium chelator BAPTA-AM (33.3 microM) alone suppressed PS without reversing TG- or caffeine-induced inhibition of PS, indicating that the suppression of PS was caused by a depletion of ER calcium stores and not by an increase in cytosolic calcium activity. TG-treatment of cells induced a complete disaggregation of polysomes which was not reversed within the 4 h recovery period following TG-treatment. After caffeine treatment of cells, we observed a heterogenous pattern of ribosomal aggregation: in some neurons ribosomes were almost completely aggregated while in other cells a significant portion of polyribosomes were disaggregated. The results indicate that a depletion of neuronal ER calcium stores disturbs protein synthesis in a similar way to the effects of transient forms of metabolic stress (ischemia, hypoglycemia or status epilepticus), thus implying that a disturbance in ER calcium homeostasis may contribute to the pathological process of stress-induced cell injury.
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PMID:Relation of neuronal endoplasmic reticulum calcium homeostasis to ribosomal aggregation and protein synthesis: implications for stress-induced suppression of protein synthesis. 943 27

Intracellular Ca2+ concentration ([Ca2+]i) was measured by Fura 2/AM fluorescence imaging microscopy in freshly isolated valvular endothelial cells taken from female and male rats. The basal level of [Ca2+]i was significantly elevated in female valvular endothelial cells when compared to males (P < 0.05). Inhibition of the sarco-endoplasmic reticulum Ca(2+)-ATPase with cyclopiazonic acid (CPA, 10 microM) caused a greater increase in the [Ca2+]i in female than male endothelial cells. Removal of extracellular Ca2+ returned the [Ca2+]i to the basal level. The rate of [Ca2+]i decline was significantly slower in female endothelial cells compared to males. There were no differences in the unstimulated rate of Mn2+ quenching between two groups. These results demonstrate that estrogen affects NOS at least in part, by an alteration in Ca2+ homeostasis in endothelial cells.
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PMID:Gender difference in the basal intracellular Ca2+ concentration in rat valvular endothelial cells. 970 27

Ca2+ loss from the sarcoplasmic reticulum (SR) of rabbit inferior vena cava smooth muscle was monitored by measuring the decay of caffeine-induced fura-2 fluorescence transients. Removal of Ca2+ from the extracellular space caused a rapid loss of SR Ca2+ and a decline of cytoplasmic Ca2+ concentration ([Ca2+]i). Simultaneous removal of extracellular Na+ greatly inhibited the rate of this (SR) Ca2+ loss. A rapid loss of SR Ca2+ was induced by 20 microns CPA, regardless of the presence or absence of extracellular Na+ or Ca2+. These effects were not influenced by alterations in membrane potential owing to activity of Ca2(+)-activated K+ channels since 3 mM TEA had no effect on the rate of Ca2+ loss from the SR. These results indicate that when Ca2+ is removed from the extracellular space, it induces Ca2+ release from the SR towards the plasma membrane Na(+)-Ca2+ exchanger which subsequently translocates it from the junctional cytoplasmic space to the extracellular space. When the Na(+)-Ca2+ exchanger is arrested by removal of extracellular Na+ and Ca2+, Ca2+ released from the SR is re-sequestered by the sarco-endo-plasmic reticulum Ca2(+)-ATPase (SERCA). However, when both the Na(+)-Ca2+ exchanger, and, the SERCA are blocked, Ca2+ released from the SR is extruded from the cells by the plasma membrane Ca2(+)-ATPase. These results reveal a hierarchy of interaction between the different Ca2+ transporters in the SR, and cell membranes.
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PMID:Functional linkage of Na(+)-Ca2+ exchange and sarcoplasmic reticulum Ca2+ release mediates Ca2+ cycling in vascular smooth muscle. 988 81


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