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

The objective was to determine if the benzothiazepine compound CGP-37157 selectively inhibits the Na(+)-Ca2+ exchanger of cardiac mitochondria without affecting the L-type voltage-dependent calcium channel, the Na(+)-Ca2+ exchanger, or the Na(+)-K(+)-ATPase of the cardiac sarcolemma, or the Ca(2+)-ATPase of the cardiac sarcoplasmic reticulum. Mitochondrial Na(+)-Ca2+ exchange activity was determined by monitoring intramitochondrial free [Ca2+] in isolated heart mitochondria loaded with the Ca(2+)-sensitive fluorophore fura-2. CGP-37157 inhibited the activity of mitochondrial Na(+)-Ca2+ exchange in a dose-dependent manner (IC50 0.36 microM). Calcium currents were recorded by whole-cell voltage clamp in isolated neonatal ventricular myocytes. Diltiazem was able to block the recorded current completely, thus confirming the current to be exclusively L-type. CGP-37157 had no effect on the calcium current recorded under identical conditions. CGP-37157, at concentrations < or = 10 microM, had no effect on the activities of the Na(+)-Ca2+ exchanger and Na(+)-K(+)-ATPase in isolated cardiac sarcolemmal vesicles or on activity of the Ca(2+)-ATPase in isolated cardiac sarcoplasmic reticulum vesicles. The data suggest that CGP-37157 is a potent, selective, and specific inhibitor of mitochondrial Na(+)-Ca2+ exchange at concentrations < or = 10 microM.
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PMID:Selectivity of inhibition of Na(+)-Ca2+ exchange of heart mitochondria by benzothiazepine CGP-37157. 768 5

Ouabain, an Na+K+ATPase inhibitor, increases the release of acetylcholine (ACh) from various preparations in a Ca2+ -independent way. However, in other preparations the release of ACh evoked by ouabain is dependent on the presence of extracellular calcium. In the present study, we have labeled the ACh of myenteric plexus longitudinal muscles of guinea pig ileum and compared the effect of calcium channel blockers on ouabain-evoked release of [3H]ACh. Release of [3H]ACh evoked by ouabain is dose dependent and decreased markedly in the absence of calcium or in the presence of cadmium, a nonspecific calcium channel blocker. N-type calcium channel blockage by the omega-conotoxins GVIA (selective N-type calcium channel blocker) and MVIC (a nonselective calcium channel blocker) inhibited by 45 and 55%, respectively, the release of [3H]ACh. L-type calcium channel suppression by low concentrations of verapamil, nifedipine, and diltiazem had no effect on the release of [3H]ACh. The release of transmitter was also not affected significantly by nickel, a T-type calcium channel blocker. In addition, omega-agatoxin-IVA, at concentrations that block P- and Q-type calcium channels, did not affect significantly the release of [3H]ACh. Thus, extracellular Ca2+ is essential for the release of ACh induced by ouabain from guinea pig ileum myenteric plexus. In this preparation, the N-type calcium channel plays a dominant role in transmitter release evoked by inhibition of Na+K+-ATPase, but other routes of calcium entry in addition to these channels can also support the release of neurotransmitter induced by ouabain.
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PMID:Inhibition of Na+,K+-ATPase by ouabain opens calcium channels coupled to acetylcholine release in guinea pig myenteric plexus. 862 96

Extracellular guanosine 5' triphosphate (GTP) enhances nerve growth factor-dependent neurite outgrowth from rat pheochromocytoma (PC12) cells; cultures of PC12 cells exposed to GTP and nerve growth factor together contain significantly more neurite-bearing cells than do those exposed to either nerve growth factor or GTP alone [Gysbers J. W. and Rathbone M. P. (1996) Int. J. devl Neurosci. 14, 19-34]. PC12 cells contain specific cell surface binding sites for extracellular GTP, which do not bind ATP or uridine 5' triphosphate. Exposure of PC12 cells to extracellular GTP (300microM) produced a robust and sustained increase in intracellular Ca(2+) ([Ca(2+)](i)), different from the transient response to the addition of ATP. The GTP-induced [Ca(2+)](i) increase was blocked by the L-type calcium channel inhibitor, nifedipine. The L-type Ca(2+) channel inhibitors, nifedipine or verapamil, also inhibited the enhancement of neurite outgrowth by GTP, but did not affect neurite outgrowth stimulated by nerve growth factor alone. Pre-treatment of PC12 cells with ryanodine (0.5-50microM) depleted calcium from internal stores and prevented the further release of calcium by GTP. Similarly, pre-treatment of PC12 cells with thapsigargin (an inhibitor of internal store Ca(2+)/ATPase) or dantrolene (which blocks Ca(2+) release from some of these stores) also reduced the enhancement of neurite outgrowth by GTP. Therefore, Ca(2+)-induced Ca(2+) release from specific stores, present in PC12 cells, is involved in the enhancement of nerve growth factor-induced neurite outgrowth by GTP, possibly acting at specific binding sites on the cell surface. GTP is proving to be an important extracellular trophic modulator in the central nervous system. These studies show that the neuritogenic actions of GTP involve moderate but sustained increases in intracellular Ca(2+) which are likely due to activation of L-type Ca(2+) channels and Ca(2+)-induced Ca(2+) release from intracellular stores. These effects of extracellular GTP are likely mediated at the cell surface and may be related to specific GTP binding sites which are distinct from G-proteins and from hitherto described purine nucleotide (P2) receptors. These data indicate a mechanism whereby the neuritogenic effects of GTP are mediated and emphasize the importance of considering GTP as a neurotrophic mediator.
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PMID:Extracellular guanosine 5' triphosphate enhances nerve growth factor-induced neurite outgrowth via increases in intracellular calcium. 1072 99

The effect of the muscarinic receptors agonist carbachol (Cch) on intracellular calcium concentration ([Ca(2+)](i)) and cAMP level was studied in polarized Fischer rat thyroid (FRT) epithelial cells. Cch provoked a transient increase in [Ca(2+)](i), followed by a lower sustained phase. Thapsigargin, a specific microsomal Ca(2+)-ATPase inhibitor, caused a rapid rise in [Ca(2+)](i) and subsequent addition of Cch was without effect. Removal of extracellular Ca(2+) reduced the initial transient response and completely abolished the plateau phase. Ryanodine, an agent that depletes intracellular Ca(2+) stores through stimulation of ryanodine receptors (RyRs), had no effect on [Ca(2+)](i). However, the transitory activation of [Ca(2+)](i) was dose-dependently attenuated in cells pretreated with U73122, a specific inhibitor of phospholipase C (PLC). These data suggest that the Cch-stimulated increment of [Ca(2+)](i) required IP(3) formation and binding to its specific receptors in Ca(2+) stores. Further studies were performed to investigate whether the effect of Cch on Ca(2+) entry into FRT cells was via L-type voltage-dependent Ca(2+) channels (L-VDCCs). Nicardipine, a nonspecific L-type Ca(2+) channel blocker, decreased Cch-induced increase on [Ca(2+)](i), while Bay K-8644, an L-type Ca(2+) channel agonist, slightly increased [Ca(2+)](i) in FRT cells. These data indicate that Ca(2+) entry into these nondifferentiated thyroid cells occurs through an L-VDCC, and probably through another mechanism such as a capacitative pathway. Cch did not affect the intracellular cAMP levels, but its effects on [Ca(2+)](i) were significantly reduced when cells were pretreated with forskolin, suggesting the existence of an intracellular cross-talk between PLC and cAMP mechanisms in the regulation of intracellular Ca(2+) mobilization in neoplastic FRT cells.
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PMID:Activation of muscarinic acetylcholine receptors induces Ca(2+) mobilization in FRT cells. 1128 59

The effect of carbachol (Cch) on intracellular calcium concentration ([Ca2+]i) in eel enterocytes was examined using the fluorescent Ca2+ indicator fura-2. Cch caused a biphasic increase in [Ca2+]i, with an initial spike followed by a progressively decreasing level (over 6 min) to the initial, pre-stimulated, level. The effect of Cch was dose-dependent with a 7.5-fold increase in [Ca2+]i over basal level induced by the maximal dose of Cch (100 microM). In Ca2+-free/EGTA buffer the effect of Cch was less pronounced and the [Ca2+]i returned rapidly to basal levels. The increment of [Ca2+]i was dose-dependently attenuated in cells pre-treated with U73122, a specific inhibitor of phospholipase C, suggesting that the Cch-stimulated increment of [Ca2+]i required inositol triphosphate formation. In the presence of extracellular Ca2+, thapsigargin (TG), a specific microsomal Ca2+-ATPase inhibitor, caused a sustained rise in [Ca2+]i whereas in Ca2+-free medium the increase in [Ca2+]i was transient; in both cases, subsequent addition of Cch was without effect. When 2 mM CaCl2 were added to the cells stimulated with TG or with Cch in Ca2+-free medium, a rapid increase in [Ca2+]i was detected, corresponding to the capacitative Ca2+ entry. Thus, both TG and Cch depleted intracellular Ca2+ stores and stimulated influx of extracellular Ca2+ consistent with capacitative Ca2+ entry. K+ depolarization obtained with increasing concentrations of KCl in the extracellular medium induced a dose-related increase in [Ca2+]i which was blocked by 2 microM nifedipine, a non-specific L-type Ca2+ channel blocker. Nifedipine also changed significantly the height of the Ca2+ transient, and the rate of decrement to the pre-stimulated [Ca2+]i level, indicating that Ca2+ entry into enterocytes also occurs through an L-type voltage-dependent calcium channel pathway. We also show that isolated enterocytes stimulated with increasing Cch concentrations (0.1-1000 microM) showed a dose-dependent inhibition of the Na+/K+-ATPase activity. The threshold decrease was at 1 microM Cch; it reached a maximum at 100 microM (50.5% inhibition) and did not decrease further with the use of higher dose. The effect of Cch on Na+/K+-ATPase activity was dependent on both protein kinase C (PKC) and protein phosphatase calcineurin activation since the PKC inhibitor calphostin C abolished Cch effects, while the calcineurin inhibitor FK506 augmented Cch effect. Collectively, these data establish a functional pathway by which Cch can modulate the activity of the Na+/K+-ATPase through a PKC-dependent (calphostin C-sensitive) pathway and a calcineurin-dependent (FK506-sensitive) pathway.
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PMID:Muscarinic acetylcholine receptor activation induces Ca2+ mobilization and Na+/K+-ATPase activity inhibition in eel enterocytes. 1201 Jun 40

The small G protein Ras-mediated signaling pathway has been implicated in the development of hypertrophy and diastolic dysfunction in the heart. Earlier cellular studies have suggested that the Ras pathway is responsible for reduced L-type calcium channel current and sarcoplasmic reticulum (SR) calcium uptake associated with sarcomere disorganization in neonatal cardiomyocytes. In the present study, we investigated the in vivo effects of Ras activation on cellular calcium handling and sarcomere organization in adult ventricular myocytes using a newly established transgenic mouse model with targeted expression of the H-Ras-v12 mutant. The transgenic hearts expressing activated Ras developed significant hypertrophy and postnatal lethal heart failure. In adult ventricular myocytes isolated from the transgenic hearts, the calcium transient was significantly depressed but membrane L-type calcium current was unchanged compared with control littermates. The expressions of sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA)2a and phospholamban (PLB) were significantly reduced at mRNA levels. The amount of SERCA2a protein was also modestly reduced. However, the expression of PLB protein and gross sarcomere organization remained unchanged in the hypertrophic Ras hearts, whereas Ser(16) phosphorylation of PLB was dramatically inhibited in the Ras transgenic hearts compared with controls. Hypophosphorylation of PLB was also associated with a significant induction of protein phosphatase 1 expression. Therefore, our results from this in vivo model system suggest that Ras-induced contractile defects do not involve decreased L-type calcium channel activities or disruption of sarcomere structure. Rather, suppressed SR calcium uptake due to reduced SERCA2a expression and hypophosphorylation of PLB due to changes in protein phosphatase expression may play important roles in the diastolic dysfunction of Ras-mediated hypertrophic cardiomyopathy.
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PMID:Sarcoplasmic reticulum calcium defect in Ras-induced hypertrophic cardiomyopathy heart. 1296 87

5-Hydroxytryptamine (5-HT) is a potent pulmonary vasoconstrictor and contributes to hypoxic pulmonary vasoconstriction and pulmonary arterial hypertension. Small intrapulmonary vessels are very sensitive to hypoxia and play a major role for blood flow regulation in the lung. Thus we have investigated the mechanisms involved in the calcium signal to 5-HT in rat small intrapulmonary artery (IPA). Effects of 5-HT were examined in isolated IPA (external diameter <250 microm) from rat. Digital imaging with fura-PE3 was used to record intracellular calcium concentration ([Ca(2+)](i)) and to follow external diameter of the vessels. 5-HT induced a sustained [Ca(2+)](i) variation that was sensitive to the inhibitor of the 5-HT(2A) receptors, ketanserin, and insensitive to voltage-dependent L-type calcium channel blockers (nitrendipine and nicardipine) or voltage-independent calcium channel antagonists (LOE-908, SKF-96365, and gadolinium). The calcium response to 5-HT was also not modified by a sarcoplasmic reticulum Ca(2+)-ATPase inhibitor (cyclopiazonic acid; CPA), which depletes intracellular calcium stores. CPA alone activated a capacitative calcium channel that was sensitive to LOE-908 and insensitive to SKF-96365 and gadolinium. The sustained calcium signal to 5-HT was partly blocked by inhibitors of arachidonic acid production (RHC-80267 and isotetrandrine) and mimicked by application of exogenous arachidonic acid. These results suggest that activation of a noncapacitative, arachidonic acid-sensitive, receptor-operated calcium channel contributes to 5-HT-induced sustained calcium increase in small IPA.
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PMID:5-HT induces an arachidonic acid-sensitive calcium influx in rat small intrapulmonary artery. 1475 48

Intracellular free Ca2+ levels are critical to the activity of BK channels in inner ear type I spiral ligament fibrocytes. However, the mechanisms for regulating intracellular Ca2+ levels in these cells are currently poorly understood. Using patch-clamp technique, we have identified a voltage-dependent L-type Ca2+ channel in type I spiral ligament fibrocytes cultured from gerbil inner ear. With 10 mM Ba2+ as the conductive cation, an inwardly rectifying current was elicited with little inactivation by membrane depolarization. The voltage activation threshold and the half-maximal voltage activation were -40 and -6 mV, respectively. This inward whole-cell current reached its peak at around 10 mV of membrane potential. The amplitude of the peak current varied among cells ranging from 50 to 274 pA with an average of 132.4 +/- 76.2 pA (n = 19); 10(-6) M nifedipine significantly inhibited the inward currents by 90.3 +/- 1.2% (n = 11). RT-PCR analysis revealed that cultured type I spiral ligament fibrocytes express the alpha1C isoform of the L-type Ca2+ channels encoded by the Cav1.2 gene. The expression of this channel in gerbil inner ear was confirmed by RT-PCR analysis using freshly isolated spiral ligament tissues. The Cav1.2 channel may function in conjunction with a previously identified intracellular Ca-ATPase (SERCA) to regulate intracellular free Ca2+ levels in type I spiral ligament fibrocytes, and thus modulate BK channel activity in these cells.
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PMID:Identification and characterization of an L-type Cav1.2 channel in spiral ligament fibrocytes of gerbil inner ear. 1519 21

We have previously shown that endothelin (ET)-1 stimulates corticosterone and aldosterone secretion by the frog adrenal gland through activation of ETA receptors positively coupled to both the adenylyl cyclase and phospholipase C (PLC) pathways. The purpose of the present study was to investigate the involvement of calcium in ET-1-induced stimulation of corticosteroid secretion. Cytoautoradiographic labeling using [125I]ET-1 as a tracer revealed the presence of ET-1 binding sites on adrenocortical cells. Administration of graded concentrations of ET-1 in the vicinity of adrenocortical cells provoked a dose-dependent increase in cytosolic calcium concentrations ([Ca2+]i). ET-1 induced a biphasic response consisting of an immediate and transient peak of [Ca2+]i followed by a plateau phase. Preincubation of the cells with the calcium-ATPase inhibitor thapsigargin or the PLC inhibitor U-73122 reduced the amplitude of the transient phase. Administration of the calcium chelator EGTA or the protein kinase A inhibitor H-89 attenuated the plateau phase. The [Ca2+]i response to ET-1 was markedly reduced during concomitant administration of U-73122 and H-89. Preincubation of the cells with the L-type calcium channel blocker nifedipine attenuated the plateau phase. Corticosteroid secretion from perifused frog adrenal slices was almost completely suppressed by thapsigargin and reduced by nifedipine. Taken together, these data indicate that activation of ETA receptors in frog adrenocortical cells provokes immediate stimulation of PLC, which causes an early mobilization of calcium from intracellular stores, and activates adenylyl cyclase, which results in delayed calcium influx through L-type calcium channels. The resulting increase in [Ca2+]i plays a pivotal role in ET-1-induced corticosteroid secretion.
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PMID:Activation of endothelinA receptors in frog adrenocortical cells stimulates both calcium mobilization from intracellular stores and calcium influx through L-type calcium channels. 1538 47

Epidemiological data document that regular exercise protects against the morbidity and mortality associated with ischemic heart disease. Therefore, we tested the hypothesis that daily exercise (DE) increases the ventricular arrhythmia threshold (VAT) induced by coronary artery occlusion and alters the expression of calcium regulatory proteins. The VAT was defined as the time from coronary occlusion to sustained ventricular tachycardia resulting in a reduction in arterial pressure. To test this hypothesis, we recorded the VAT in conscious sedentary normotensive, sedentary hypertensive, and DE hypertensive rats, and we associated these thresholds with the protein expression of the L-type calcium channel, Na+/Ca2+ exchanger, phospholamban, and sarco(endo)plasmic reticulum Ca(2+)-ATPase. Results document a significantly reduced time to ventricular arrhythmias (sedentary hypertensive, 3.7 +/- 0.3 min vs. sedentary normotensive, 4.8 +/- 0.3 min), an increased Na+/Ca2+ exchanger protein expression (47%), and a decreased phospholamban protein expression (-34%) in conscious hypertensive rats. DE increased the VAT (5.9 +/- 0.2 min), decreased the protein expression of the Na+/Ca2+ exchanger, and normalized the protein expression of phospholamban in the hypertensive rats. Thus DE may be a primary prevention approach for reducing the incidence of arrhythmias by altering calcium regulatory proteins in hypertensive rats.
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PMID:Daily exercise-induced cardioprotection is associated with changes in calcium regulatory proteins in hypertensive rats. 1547 72


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