Twitch-dependent SR Ca accumulation and release in rabbit ventricular myocytes

1993 ◽  
Vol 265 (2) ◽  
pp. C533-C540 ◽  
Author(s):  
J. W. Bassani ◽  
R. A. Bassani ◽  
D. M. Bers
Keyword(s):  
Steady State ◽  
Ventricular Myocytes ◽  
State Level ◽  
Exposure Period ◽  
Steady State Level ◽  
Fluorescent Indicator ◽  
Intracellular Ca ◽  
Rabbit Ventricular Myocytes ◽  
Time Required ◽  
Ca Depletion

Using caffeine-induced contractures (Ccaf) and thapsigargin (TG), we estimated the fraction of sarcoplasmic reticulum (SR) Ca released at one twitch and also the number of twitches required to reload a Ca-depleted SR. Similar results were obtained for twitches or intracellular Ca (Cai) transient with the fluorescent indicator, indo 1. Sustained exposure to 10 mM caffeine completely depletes the SR of Ca in < 5 s (as assessed by a second Ccaf). After such Ca depletion, four to five twitches are necessary to reload the SR to the steady-state level (with a twitch constant, tau = 1.6 twitches). We also determined the time required for complete inhibition of the SR Ca-adenosinetriphosphatase (ATPase) by TG. After SR Ca depletion, 5 microM TG was applied for different periods of time before a train of "reloading" twitches. A TG exposure period of 90 s was sufficient to completely prevent Ccaf after these reloading twitches. When SR is Ca depleted, the twitch is larger in the presence of TG, indicating that the SR Ca-ATPase can limit the ability of Ca influx to activate contraction. To assess SR Ca released at one twitch in cells with normally Ca-loaded SR, 5 microM TG was applied for 90 s to prevent SR Ca reuptake. Then one or several twitches were activated (causing SR Ca release, but with reuptake completely blocked). After the twitch (or train), a Ccaf was used to assess remaining SR Ca.(ABSTRACT TRUNCATED AT 250 WORDS)

scholarly journals Post-translational processing of urea amidolyase in Saccharomyces cerevisiae.

1982 ◽  
Vol 2 (7) ◽  
pp. 800-804 ◽  
Author(s):  
R A Sumrada ◽  
G Chisholm ◽  
T G Cooper
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Steady State ◽  
State Level ◽  
Steady State Level ◽  
Prosthetic Group ◽  
Apparent Paradox ◽  
Multifunctional Protein ◽  
Group A ◽  
Time Required ◽  
Sequential Induction

Urea amidolyase catalyzes the two reactions (urea carboxylase and a allophanate hydrolase) associated with urea degradation in Saccharomyces cerevisiae. Past work has shown that both reactions are catalyzed by a 204-kilodalton, multifunctional protein. In view of these observations, it was surprising to find that on induction at 22 degrees C, approximately 2 to 6 min elapsed between the appearance of allophanate hydrolase and urea carboxylase activities. In search of an explanation for this apparent paradox, we determined whether or not a detectable period of time elapsed between the appearance of allophanate hydrolase activity and activation of the urea carboxylase domain by the addition of biotin. We found that a significant portion of the protein produced immediately after the onset of induction lacked the prosthetic group. A steady-state level of biotin-free enzyme was reached 16 min after induction and persisted indefinitely thereafter. These data are consistent with the suggestion that sequential induction of allophanate hydrolase and urea carboxylase activities results from the time required to covalently bind biotin to the latter domain of the protein.

Influence of prior Na+ pump activity on pump and Na+/Ca2+exchange currents in mouse ventricular myocytes

1998 ◽  
Vol 275 (5) ◽  
pp. H1808-H1817 ◽  
Author(s):  
Zhi Su ◽  
Anruo Zou ◽  
Akihiko Nonaka ◽  
Iram Zubair ◽  
Michael C. Sanguinetti ◽  
...  
Keyword(s):  
Steady State ◽  
Concentration Gradient ◽  
Ventricular Myocytes ◽  
State Level ◽  
Pump Current ◽  
Steady State Level ◽  
Peak Current ◽  
Na Pump ◽  
Patch Pipette ◽  
Pump Activity

We examined the dependence of peak Na+ pump and Na+/Ca2+exchanger currents on prior Na+pump inhibition induced by exposure to zero extracellular K+ in voltage-clamped adult murine ventricular myocytes. Abrupt activation of the Na+ pump by reexposure of myocytes to extracellular K+ with a rapid solution switcher resulted in the development of a transient peak current at ∼500 ms, followed by a decline over 1–2 min to a steady-state level. The magnitudes of both the peak Na+ pump current ( I p) and the peak outward Na+/Ca2+exchange current, activated by rapidly reducing extracellular Na+ to zero with the solution switcher, were dependent on previous Na+ pump activity. [Na+] gradients (Na+-binding benzofuran isophthalate fluorescence) between the patch pipette and the bulk cytosol were relatively small and could not account for the large differences between peak and steady-state I p and reverse Na+/Ca2+exchanger currents. Our results are consistent with the presence of a subsarcolemmal Na+ concentration gradient, which is similar for the Na+ pump and the Na+/Ca2+exchanger. These findings also support the hypothesis that the Na+ pump and the Na+/Ca2+exchanger are colocalized in the sarcolemma.

Post-translational processing of urea amidolyase in Saccharomyces cerevisiae

1982 ◽  
Vol 2 (7) ◽  
pp. 800-804
Author(s):  
R A Sumrada ◽  
G Chisholm ◽  
T G Cooper
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Steady State ◽  
State Level ◽  
Steady State Level ◽  
Prosthetic Group ◽  
Apparent Paradox ◽  
Multifunctional Protein ◽  
Group A ◽  
Time Required ◽  
Sequential Induction

Urea amidolyase catalyzes the two reactions (urea carboxylase and a allophanate hydrolase) associated with urea degradation in Saccharomyces cerevisiae. Past work has shown that both reactions are catalyzed by a 204-kilodalton, multifunctional protein. In view of these observations, it was surprising to find that on induction at 22 degrees C, approximately 2 to 6 min elapsed between the appearance of allophanate hydrolase and urea carboxylase activities. In search of an explanation for this apparent paradox, we determined whether or not a detectable period of time elapsed between the appearance of allophanate hydrolase activity and activation of the urea carboxylase domain by the addition of biotin. We found that a significant portion of the protein produced immediately after the onset of induction lacked the prosthetic group. A steady-state level of biotin-free enzyme was reached 16 min after induction and persisted indefinitely thereafter. These data are consistent with the suggestion that sequential induction of allophanate hydrolase and urea carboxylase activities results from the time required to covalently bind biotin to the latter domain of the protein.

Tacrolimus initial steady state level in post-transplant cyclophosphamide-based GvHD prophylaxis regimens

2021 ◽  
Author(s):  
Janny M. Yao ◽  
Dongyun Yang ◽  
Mary C. Clark ◽  
Salman Otoukesh ◽  
Thai Cao ◽  
...  
Keyword(s):  
Steady State ◽  
State Level ◽  
Steady State Level ◽  
Post Transplant ◽  
Gvhd Prophylaxis

Steady-state twitch Ca2+ fluxes and cytosolic Ca2+ buffering in rabbit ventricular myocytes

1996 ◽  
Vol 270 (1) ◽  
pp. C192-C199 ◽  
Author(s):  
L. M. Delbridge ◽  
J. W. Bassani ◽  
D. M. Bers
Keyword(s):  
Steady State ◽  
Sarcoplasmic Reticulum ◽  
Voltage Clamp ◽  
Ventricular Myocytes ◽  
Cell Voltage ◽  
Whole Cell ◽  
Rabbit Ventricular Myocytes ◽  
The Mean ◽  
State Contraction ◽  
Caffeine Contractures

Intracellular Ca2+ ([Ca2+]i) transients and transsarcolemmal Ca2+ currents were measured in indo 1-loaded isolated rabbit ventricular myocytes during whole cell voltage clamp to quantitate the components of cytosolic Ca2+ influx and to describe the dynamic aspects of cytosolic Ca2+ buffering during steady-state contraction (0.5 Hz, 22 degrees C). Sarcolemmal Ca2+ influx was directly measured from the integrated Ca2+ current (Ica) recorded during the clamp (158 +/- 10 attomoles; amol). Sarcoplasmic reticulum (SR) Ca2+ content was determined from the integrated electrogenic Na+/Ca2+ exchange current (Ix) induced during rapid application and sustained exposure of cells to caffeine to elicit the release of the SR Ca2+ load (1,208 +/- 170 amol). The mean steady-state SR Ca2+ load was calculated to be 87 +/- 13 microM (mumol/l nonmitochondrial cytosolic volume). Ca2+ influx via Ica represented approximately 14% of the stored SR Ca2+ and 23% of the total cytosolic Ca2+ flux during a twitch (47 +/- 6 microM). Comparison of electrophysiologically measured Ca2+ fluxes with Ca2+ transients yields apparent buffering values of 60 for caffeine contractures and 110 for twitches (delta Ca2+ total/delta Ca2+ free). This is consistent with the occurrence of "active" buffering of cytosolic Ca2+ by SR Ca2+ uptake during the twitch.

Ascorbate and glutathione homeostasis in vascular smooth muscle cells: cooperation with endothelial cells

1998 ◽  
Vol 275 (4) ◽  
pp. C1031-C1039 ◽  
Author(s):  
Ilia Voskoboinik ◽  
Karin Söderholm ◽  
Ian A. Cotgreave
Keyword(s):  
Endothelial Cells ◽  
Smooth Muscle ◽  
Steady State ◽  
Smooth Muscle Cells ◽  
Umbilical Vein ◽  
State Level ◽  
Muscle Cells ◽  
Free Access ◽  
Steady State Level ◽  
Human Umbilical Vein

Human umbilical vein smooth muscle cells (HUVSMCs) utilize extracellular cystine, glutathione (GSH), and N-acetylcysteine (NAC) to synthesize cellular GSH. Extracellular cystine was effective from 5 μM, whereas GSH and NAC were required at 100 μM for comparable effects. The efficacy of extracellular GSH was dependent on de novo GSH synthesis, indicating a dependence on cellular γ-glutamyltransferase (glutamyl transpeptidase). Coculture of syngenetic HUVSMCs and corresponding human umbilical vein endothelial cells (HUVECs) on porous supports restricted cystine- or GSH-stimulated synthesis of HUVSMC GSH when supplied on the “luminal” endothelial side. Thus HUVSMC GSH rapidly attained a steady-state level below that achieved in the absence of interposed HUVECs. HUVSMCs also readily utilize both reduced ascorbate (AA) and oxidized dehydroascorbate (DHAA) over the range 50–500 μM. Phloretin effectively blocked both AA- and DHAA-stimulated assimilation of intracellular AA, indicating a role for a glucose transporter in their transport. Uptake of extracellular AA was also sensitive to extracellular, but not intracellular, thiol depletion. When AA was applied to the endothelial side of the coculture model, assimilation of intracellular AA in HUVSMCs was restricted to a steady-state level below that achieved by free access.

scholarly journals The steady-state level of Mg-protoporphyrin IX is not a determinant of plastid-to-nucleus signaling in Arabidopsis

2008 ◽  
Vol 105 (39) ◽  
pp. 15184-15189 ◽  
Author(s):  
N. Mochizuki ◽  
R. Tanaka ◽  
A. Tanaka ◽  
T. Masuda ◽  
A. Nagatani
Keyword(s):  
Steady State ◽  
Protoporphyrin Ix ◽  
State Level ◽  
Steady State Level
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