Cyclopiazonic Acid Effect on Ca2+-Dependent Conformational States of the Sarcoplasmic Reticulum ATPase. Implication for the Enzyme Turnover†

Biochemistry ◽  
1998 ◽  
Vol 37 (12) ◽  
pp. 4266-4274 ◽  
Author(s):  
Fernando Soler ◽  
Fernando Plenge-Tellechea ◽  
Isabel Fortea ◽  
Francisco Fernandez-Belda
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Cyclopiazonic Acid ◽  
Conformational States ◽  
Acid Effect ◽  
Enzyme Turnover

Na+ entry via store-operated channels modulates Ca2+signaling in arterial myocytes

2000 ◽  
Vol 278 (1) ◽  
pp. C163-C173 ◽  
Author(s):  
Assaf Arnon ◽  
John M. Hamlyn ◽  
Mordecai P. Blaustein
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Cyclopiazonic Acid ◽  
General Mechanism ◽  
Tetraacetic Acid ◽  
Pump Activity ◽  
In Cells

In many nonexcitable cells, hormones and neurotransmitters activate Na+ influx and mobilize Ca2+ from intracellular stores. The stores are replenished by Ca2+influx via “store-operated” Ca2+ channels (SOC). The main routes of Na+ entry in these cells are unresolved, and no role for Na+ in signaling has been recognized. We demonstrate that the SOC are a major Na+ entry route in arterial myocytes. Unloading of the Ca2+stores with cyclopiazonic acid (a sarcoplasmic reticulum Ca2+ pump inhibitor) and caffeine induces a large external Na+-dependent rise in the cytosolic Na+ concentration. One component of this rise in cytosolic Na+ concentration is likely due to Na+/Ca2+exchange; it depends on elevation of cytosolic Ca2+ and is insensitive to 10 mM Mg2+ and 10 μM La3+. Another component is inhibited by Mg2+ and La3+, blockers of SOC; this component persists in cells preloaded with 1,2-bis(2-aminophenoxy)ethane- N, N, N′, N′-tetraacetic acid to buffer Ca2+ transients and prevent Na+/Ca2+exchange-mediated Na+ entry. This Na+ entry apparently is mediated by SOC. The Na+ entry influences Na+ pump activity and Na+/Ca2+exchange and has unexpectedly large effects on cell-wide Ca2+ signaling. The SOC pathway may be a general mechanism by which Na+ participates in signaling in many types of cells.

scholarly journals Energy expenditure by Ba2+contracture in rat ventricular slices derives from cross-bridge cycling

1999 ◽  
Vol 277 (1) ◽  
pp. H74-H79 ◽  
Author(s):  
Hisaharu Kohzuki ◽  
Hiromi Misawa ◽  
Susumu Sakata ◽  
Yoshimi Ohga ◽  
Hiroyuki Suga ◽  
...  
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Energy Expenditure ◽  
Cyclopiazonic Acid ◽  
Left Ventricular ◽  
Basal Metabolism ◽  
Dependent Manner ◽  
Tyrode Solution ◽  
Cross Bridge ◽  
Butanedione Monoxime ◽  
Dose Dependent

To clarify the energy-expenditure mechanism during Ba2+ contracture of mechanically unloaded rat left ventricular (LV) slices, we measured myocardial O2 consumption (V˙o 2) of quiescent slices in Ca2+-free Tyrode solution andV˙o 2 during Ba2+ contracture by substituting Ca2+ with Ba2+. We then investigated the effects of cyclopiazonic acid (CPA) and 2,3-butanedione monoxime (BDM) on the Ba2+ contractureV˙o 2. The Ca2+-freeV˙o 2 corresponds to that of basal metabolism (2.32 ± 0.53 ml O2 ⋅ min−1 ⋅ 100 g LV−1). Ba2+ increased theV˙o 2 in a dose-dependent manner (from 0.3 to 3.0 mmol/l) from 110 to 150% of basal metabolic V˙o 2. Blockade of the sarcoplasmic reticulum (SR) Ca2+ pump by CPA (10 μmol/l) did not at all decrease the Ba2+-activatedV˙o 2. BDM (5 mmol/l), which specifically inhibits cross-bridge cycling, reduced the Ba2+activatedV˙o 2 almost to basal metabolic V˙o 2. These energetic results revealed that the Ba2+-activatedV˙o 2 was used for the cross-bridge cycling but not for the Ca2+ handling by the SR Ca2+ pump.

Nordexfenfluramine causes more severe pulmonary vasoconstriction than dexfenfluramine

2004 ◽  
Vol 286 (3) ◽  
pp. L531-L538 ◽  
Author(s):  
Zhigang Hong ◽  
Andrea Olschewski ◽  
Helen L. Reeve ◽  
Daniel P. Nelson ◽  
Fangxiao Hong ◽  
...  
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Pulmonary Arteries ◽  
Cyclopiazonic Acid ◽  
Cytosolic Calcium ◽  
Ring Contraction ◽  
Pulmonary Vasoconstriction ◽  
Reduced Ring ◽  
Dose Dependent Decrease ◽  
Trisphosphate Receptor ◽  
Dose Dependent

The anorectic agent dexfenfluramine (dex) causes the development of primary pulmonary hypertension in susceptible patients by an unknown mechanism. We compared the effects of dex with those of its major metabolite, nordexfenfluamine (nordex), in the isolated perfused rat lung and in isolated rings of resistance pulmonary arteries. Nordex caused a dose-dependent and more intense vasoconstriction, which can be inhibited by the nonspecific 5-hydroxytryptamine type 2 (5-HT2) blocker ketanserin. Similarly a rise in cytosolic calcium concentration ([Ca2+]i) in dispersed pulmonary artery smooth muscle cells (PASMCs) induced by nordex could be prevented by ketanserin. Unlike prior observations with dex, nordex did not inhibit K+ current or cause depolarization in PASMCs. Removal of Ca2+ from the tissue bath or addition of nifedipine (1 μM) reduced ring contraction to nordex by 60 ± 9 and 63 ± 4%, respectively. The addition of 2-aminoethoxydiphenyl borate (2-APB), a blocker of store-operated channels and the inositol 1,4,5-trisphosphate receptor, caused a dose-dependent decrease in the ring contraction elicited by nordex. The combination of 2-APB (10 μM) and nifedipine (1 μM) completely ablated the nordex contraction. Likewise the release of Ca2+ from the sarcoplasmic reticulum by cyclopiazonic acid markedly reduced the nordex contraction while leaving the KCl contraction unchanged. We conclude that nordex may be responsible for much of the vasoconstriction stimulated by dex, through the activation of 5-HT2 receptors and that the [Ca2+]i increase in rat PASMCs caused by dex/nordex is due to both influx of extracellular Ca2+ and release of Ca2+ from the sarcoplasmic reticulum.

Evidence for two types of internal Ca2+ stores in canine mesenteric artery with different refilling mechanisms

1992 ◽  
Vol 262 (1) ◽  
pp. H31-H37 ◽  
Author(s):  
A. M. Low ◽  
C. Y. Kwan ◽  
E. E. Daniel
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Mesenteric Artery ◽  
Cyclopiazonic Acid ◽  
Bay K 8644 ◽  
Krebs Solution ◽  
Tetraacetic Acid ◽  
Free Medium ◽  
Phenylephrine Hydrochloride ◽  
Dog Mesenteric Artery ◽  
Biphasic Responses

Novel transient biphasic responses of the dog mesenteric artery to phenylephrine hydrochloride (PE, 10 microM) in Ca(2+)-free medium containing 50 microM ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA) have been analyzed. The initial component was significantly inhibited by ryanodine (30-100 microM), an agonist enhancing Ca2+ release from the sarcoplasmic reticulum, whereas the second was significantly inhibited by nifedipine (1 microM), and L-type Ca2+ channel antagonist, or EGTA, to chelate Ca2+, and was potentiated by BAY K 8644 (1 microM), an L-type Ca2+ channel agonist. After repletion of Ca2+ stores in normal Krebs solution or in high KCl (60 mM) Krebs, the first component was inhibited by cyclopiazonic acid (CPA, 30 microM), a putative, reversible, and selective microsomal Ca2+ pump adenosinetriphosphatase inhibitor. BAY K 8644 potentiated the second component in the presence of CPA. The inhibition of the first component by CPA suggests that the refilling ultimately requires the CPA-sensitive Ca2+ pump for Ca2+ resequestration. However, the second component may refill by a CPA-independent route opened by BAY K 8644. These results, taken as a whole, indicate that the biphasic PE response in Ca(2+)-free medium may reflect compartmentalization of Ca2+ storage related to the different routes of refilling.

scholarly journals Sarcoplasmic reticulum and endothelium independently regulate venous smooth muscle [Ca2+]iand contraction

1999 ◽  
Vol 277 (2) ◽  
pp. H749-H755
Author(s):  
Régent Laporte ◽  
Ismail Laher
Keyword(s):  
Smooth Muscle ◽  
Steady State ◽  
Sarcoplasmic Reticulum ◽  
Salt Solution ◽  
Isometric Contraction ◽  
Cyclopiazonic Acid ◽  
Physiological Salt Solution ◽  
Sustained Contraction ◽  
Facial Vein ◽  
State Increase

In rings of rabbit facial vein (RFV), depletion of sarcoplasmic reticulum (SR) Ca2+ by caffeine abolished the subsequent isometric contraction to 25 mM K+ physiological salt solution (25K-PSS). However, the associated steady-state increase of smooth muscle intracellular free Ca2+concentration ([Ca2+]i), measured using fura PE3 and cuvette photometry, was not altered. Treatment with the specific SR Ca2+ pump inhibitor cyclopiazonic acid (30 μM) after caffeine-induced SR Ca2+ depletion restored and greatly augmented the 25K-PSS-induced contraction. This suggests that SR Ca2+ depletion leads to a dissociation of K+-induced [Ca2+]iincrease from contraction that was dependent on Ca2+ pump-mediated SR Ca2+ uptake. Endothelium removal augmented the 25K-PSS-induced [Ca2+]iincrease after caffeine-induced SR Ca2+ depletion. However, this was associated with only a small and transient contraction. Exposure of endothelium-denuded RFV to cyclopiazonic acid after caffeine-induced SR Ca2+ depletion further amplified the 25K-PSS-induced [Ca2+]iincrease, which was associated with a large and sustained contraction. However, the latter [Ca2+]iincrease was still higher than in endothelium-intact RFV. This suggests that the endothelium dampens the [Ca2+]irise associated with K+-induced Ca2+ influx, but independently of Ca2+ pump-mediated SR Ca2+ uptake.

scholarly journals Superficial buffer barrier and preferentially directed release of Ca2+ in canine airway smooth muscle

1999 ◽  
Vol 276 (5) ◽  
pp. L744-L753 ◽  
Author(s):  
Luke J. Janssen ◽  
Pierre A. Betti ◽  
Stuart J. Netherton ◽  
Denise K. Walters
Keyword(s):  
Smooth Muscle ◽  
Sarcoplasmic Reticulum ◽  
Airway Smooth Muscle ◽  
Cyclopiazonic Acid ◽  
Membrane Currents ◽  
Global Changes ◽  
Fura 2 ◽  
Mechanical Responses ◽  
Filling State

We examined cytosolic concentration of Ca2+([Ca2+]i) in canine airway smooth muscle using fura 2 fluorimetry (global changes in [Ca2+]i), membrane currents (subsarcolemmal [Ca2+]i), and contractions (deep cytosolic [Ca2+]i). Acetylcholine (10−4 M) elicited fluorimetric, electrophysiological, and mechanical responses. Caffeine (5 mM), ryanodine (0.1–30 μM), and 4-chloro-3-ethylphenol (0.1–0.3 mM), all of which trigger Ca2+-induced Ca2+ release, evoked Ca2+ transients and membrane currents but not contractions. The sarcoplasmic reticulum (SR) Ca2+-pump inhibitor cyclopiazonic acid (CPA; 10 μM) evoked Ca2+transients and contractions but not membrane currents. Caffeine occluded the response to CPA, whereas CPA occluded the response to acetylcholine. Finally, KCl contractions were augmented by CPA, ryanodine, or saturation of the SR and reduced when SR filling state was decreased before exposure to KCl. We conclude that 1) the SR forms a superficial buffer barrier dividing the cytosol into functionally distinct compartments in which [Ca2+]iis regulated independently; 2) Ca2+-induced Ca2+ release is preferentially directed toward the sarcolemma; and 3) there is no evidence for multiple, pharmacologically distinct Ca2+ pools.

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