scholarly journals Calsequestrin: more than ‘only’ a luminal Ca2+ buffer inside the sarcoplasmic reticulum

1998 ◽  
Vol 337 (1) ◽  
pp. 19-22 ◽  
Author(s):  
Csaba SZEGEDI ◽  
Sándor SÁRKÖZI ◽  
Anke HERZOG ◽  
István JÓNA ◽  
Magdolna VARSÁNYI
Keyword(s):  
Skeletal Muscle ◽  
Sarcoplasmic Reticulum ◽  
Striated Muscle ◽  
Hill Coefficient ◽  
Channel Activity ◽  
Open Probability ◽  
Physiological Event ◽  
Contraction Coupling ◽  
Open Time ◽  
The Mean

In striated muscle, the sarcoplasmic reticulum (SR) Ca2+ release/ryanodine receptor (RyR) channel provides the pathway through which stored Ca2+ is released into the myoplasm during excitation–contraction coupling. Various luminal Ca2+-binding proteins are responsible for maintaining the free [Ca2+] at 10-3–10-4 M in the SR lumen; in skeletal-muscle SR, it is mainly calsequestrin. Here we show that, depending on its phosphorylation state, calsequestrin selectively controls the RyR channel activity at 1 mM free luminal [Ca2+]. Calsequestrin exclusively in the dephosphorylated state enhanced the open probability by approx. 5-fold with a Hill coefficient (h) of 3.3, and increased the mean open time by about 2-fold, i.e. solely dephosphorylated calsequestrin regulates Ca2+ release from the SR. Because calsequestrin has been found to occur mainly in the phosphorylated state in the skeletal-muscle SR for the regulation of RyR channel activity, the dephosphorylation of calsequestrin would appear to be a quintessential physiological event.

Lactate inhibits Ca2+-activated Ca2+-channel activity from skeletal muscle sarcoplasmic reticulum

1997 ◽  
Vol 82 (2) ◽  
pp. 447-452 ◽  
Author(s):  
Terence G. Favero ◽  
, Anthony C. Zable ◽  
, David Colter ◽  
Jonathan J. Abramson
Keyword(s):  
Skeletal Muscle ◽  
Sarcoplasmic Reticulum ◽  
Single Channel ◽  
Channel Activity ◽  
Release Channel ◽  
Muscle Lactate ◽  
Tension Development ◽  
Contraction Coupling ◽  
Single Channel Activity ◽  
High Concentrations

Favero, Terence G., Anthony C. Zable, David Colter, and Jonathan J. Abramson. Lactate inhibits Ca2+-activated Ca2+-channel activity from skeletal muscle sarcoplasmic reticulum. J. Appl. Physiol. 82(2): 447–452, 1997.—Sarcoplasmic reticulum (SR) Ca2+-release channel function is modified by ligands that are generated during about of exercise. We have examined the effects of lactate on Ca2+- and caffeine-stimulated Ca2+ release, [3H]ryanodine binding, and single Ca2+-release channel activity of SR isolated from rabbit white skeletal muscle. Lactate, at concentrations from 10 to 30 mM, inhibited Ca2+- and caffeine-stimulated [3H]ryanodine binding to and inhibited Ca2+- and caffeine-stimulated Ca2+ release from SR vesicles. Lactate also inhibited caffeine activation of single-channel activity in bilayer reconstitution experiments. These findings suggest that intense muscle activity, which generates high concentrations of lactate, will disrupt excitation-contraction coupling. This may lead to decreases in Ca2+ transients promoting a decline in tension development and contribute to muscle fatigue.

Ethanol enhances caffeine-induced Ca2+-release channel activation in skeletal muscle sarcoplasmic reticulum

1997 ◽  
Vol 272 (2) ◽  
pp. C622-C627 ◽  
Author(s):  
T. Oba ◽  
M. Koshita ◽  
M. Yamaguchi
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Lipid Bilayers ◽  
Skeletal Muscles ◽  
Single Channel ◽  
Channel Activity ◽  
Electrical Parameters ◽  
Open Probability ◽  
Release Channel ◽  
Channel Current ◽  
Open Time

When sarcoplasmic reticulum (SR) vesicles prepared from frog skeletal muscles were actively loaded with Ca2+, pretreatment of the SR with 2.2 mM (0.01%) ethanol for 30 s significantly potentiated 5 mM caffeine-induced release of Ca2+ from 16.7 +/- 3.7 nmol/mg protein in control without ethanol to 28.0 +/- 2.6 nmol/mg (P < 0.05, n = 5). Ethanol alone caused no release of Ca2+ from the SR. Exposure of the Ca2+-release channel, incorporated into planar lipid bilayers, to 2 mM caffeine significantly increased open probability (Po) and mean open time, but unitary conductance was not affected. Ethanol (2.2 mM) enhanced caffeine-induced Ca2+-release channel activity, with Po reaching 3.02-fold and mean open time 2.85-fold the values in the absence of ethanol. However, ethanol alone did not affect electrical parameters of single-channel current, over a concentration range of 2.2 mM (0.01%) to 217 mM (1%). The synergistic action of ethanol and caffeine on the channel activity could be attributable to enhancement of caffeine-induced release of Ca2+ from the SR vesicles in the presence of ethanol.

Actions of sulfhydryl reagents on single ryanodine receptor Ca(2+)-release channels from sheep myocardium

1997 ◽  
Vol 272 (6) ◽  
pp. C1908-C1918 ◽  
Author(s):  
K. R. Eager ◽  
L. D. Roden ◽  
A. F. Dulhunty
Keyword(s):  
Lipid Bilayers ◽  
Ryanodine Receptor ◽  
Channel Activity ◽  
Irreversible Loss ◽  
Sulfhydryl Reagents ◽  
Open Probability ◽  
Open Time ◽  
Wide Range ◽  
The Mean ◽  
Channel Open Time

Effects of the reactive disulfides, 2,2'- and 4,4'-dithiodipyridine, on single cardiac ryanodine receptor (RyR) ion channels incorporated into lipid bilayers are reported. RyRs are activated within minutes of addition of the reactive disulfides (10(-7) to 10(-3) M) with an irreversible loss of channel activity after the activation at concentrations > or = 10(-4) M. This activation, followed by loss of activity, is seen over a wide range of cytoplasmic (cis) Ca2+ concentration between 10(-9) and 2 x 10(-2) M and occurs more rapidly with higher reactive disulfide concentrations or when RyRs are initially active at 10(-5) or 10(-3) M Ca2+. The reactive disulfides increase the channel open probability by introducing long components into the open time distributions, increasing the mean channel open time by up to 50-fold. Closed time distributions are not altered by the sulfhydryl reagents. The effects of the reactive disulfides are prevented by the reducing agents dithiothreitol and glutathione (1–10 mM). The results suggest that cysteine residues on the RyR complex can regulate the ion channel gating mechanisms.

A calcium-activated chloride channel in sarcoplasmic reticulum vesicles from rabbit skeletal muscle

1996 ◽  
Vol 270 (6) ◽  
pp. C1675-C1686 ◽  
Author(s):  
J. I. Kourie ◽  
D. R. Laver ◽  
G. P. Ahern ◽  
A. F. Dulhunty
Keyword(s):  
Skeletal Muscle ◽  
Sarcoplasmic Reticulum ◽  
Lipid Bilayers ◽  
Chloride Channel ◽  
Single Channel ◽  
Single Channels ◽  
Channel Activity ◽  
Open Probability ◽  
Single Channel Activity ◽  
Maximum Conductance

A Ca(2+)-activated Cl- channel is described in sarcoplasmic reticulum (SR) enriched vesicles of skeletal muscle incorporated into lipid bilayers. Small chloride (SCl) channels (n = 20) were rapidly and reversibly activated when cis- (cytoplasmic) [Ca2+] was increased above 10(-7) M, with trans-(luminal) [Ca2+] at either 10(-3) or 10(-7) M. The open probability of single channels increased from zero when cis-[Ca2+] was 10(-7) M to 0.61 +/- 0.12 when [Ca2+] was 10(-4) M. High- and low-conductance levels in single-channel activity were activated at different cis-[Ca2+]. Channel openings to the maximum conductance, 65-75 pS (250/50 mM Cl-, cis/ trans), were active when cis-[Ca2+] was increased above 5 x 10(-6) M. In contrast to the maximum conductance, channel openings to submaximal levels between 5 and 40 pS were activated at a lower cis-[Ca2+] and dominated channel activity between 5 x 10(-7) and 5 x 10(-6) M. Activation of SCl channels was Ca2+ specific and not reproduced by cytoplasmic Mg2+ concentrations of 10(-3) M. We suggest that the SCl channel arises in the SR membrane. The Ca2+ dependence of this channel implies that it is active at [Ca2+] achieved during muscle contraction.

Metabolic end products inhibit sarcoplasmic reticulum Ca2+ release and [3H]ryanodine binding

1995 ◽  
Vol 78 (5) ◽  
pp. 1665-1672 ◽  
Author(s):  
T. G. Favero ◽  
A. C. Zable ◽  
M. B. Bowman ◽  
A. Thompson ◽  
J. J. Abramson
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Single Channel ◽  
Oxygen Species ◽  
Channel Activity ◽  
Open Probability ◽  
Release Channel ◽  
Tension Development ◽  
Contraction Coupling ◽  
End Products ◽  
Decreasing Ph

Sarcoplasmic reticulum (SR) Ca2+ release channel function is modified by ligands (Mg2+, Ca2+, ATP, and H+) that are generated during a bout of exercise. We have examined the effects of changing intracellular metabolites on Ca2+ release, [3H]ryanodine binding, and single-Ca2+ release channel activity of SR isolated from white rabbit skeletal muscle. Increasing Mg2+ (from 0 to 4 mM) and decreasing pH (7.1–6.5) inhibited SR Ca2+ release and [3H]-ryanodine binding. In addition, increasing lactate concentrations from 2 to 20 mM inhibited [3H]ryanodine binding to SR vesicles, inhibited SR Ca2+ release, and decreased the single-channel open probability. These findings suggest that intracellular modifications that disrupt excitation-contraction coupling and decrease Ca2+ transients will promote a decline in tension development and contribute to muscle fatigue. In addition, we show that hydrogen peroxide induces Ca2+ release and increases [3H]ryanodine binding to its receptor, suggesting that reactive oxygen species produced during exercise may compromise muscle function by altering the normal gating of the SR Ca2+ release channel.

scholarly journals Proton modulation of a Ca(2+)-activated K+ channel from rat skeletal muscle incorporated into planar bilayers.

1991 ◽  
Vol 98 (5) ◽  
pp. 1025-1042 ◽  
Author(s):  
C Laurido ◽  
S Candia ◽  
D Wolff ◽  
R Latorre
Keyword(s):  
Skeletal Muscle ◽  
Linear Function ◽  
K Channel ◽  
Ca Channel ◽  
Rat Skeletal Muscle ◽  
Open Probability ◽  
Planar Bilayers ◽  
Effect Of Ph ◽  
Open Time ◽  
The Mean

The effect of pH on the activation of a Ca-activated K+ [K(Ca)] channel from rat skeletal muscle incorporated into planar lipid bilayers was studied. Experiments were done at different intracellular Ca2+ and proton concentrations. Changes in pH modified channel kinetics only from the Ca-sensitive face of the channel. At constant Ca2+ concentration, intracellular acidification induced a decrease in the open probability (Po) and a shift of the channel activation curves toward the right along the voltage axis. The displacement was 23.5 mV per pH unit. This displacement was due to a change in the half saturation voltage (Vo) and not to a change in channel voltage dependence. The shifts in Vo induced by protons appeared to be independent of Ca2+ concentration. The slope of the Hill plot of the open-closed equilibrium vs. pH was close to one, suggesting that a minimum of one proton is involved in the proton-driven channel closing reaction. The change in Po with variations in pH was due to both a decrease in the mean open time (To) and an increase in the mean closed time (Tc). At constant voltage, the mean open time of the channel was a linear function of [Ca2+] and the mean closed time was a linear function of 1/[Ca2+]2. Changes in the internal pH modified the slope, but not the intercept of the linear relations To vs. [Ca2+] and Tc vs. 1/[Ca2+]2. On the basis of these results an economical kinetic model of the effect of pH on this channel is proposed. It is concluded that protons do not affect the open-closed reaction, but rather weaken Ca2+ binding to all the conformational states of the channel. Moreover, competitive models in which Ca2+ and H+ cannot bind to the same open or closed state are inconsistent with the data.

scholarly journals Triadin Binding to the C-Terminal Luminal Loop of the Ryanodine Receptor is Important for Skeletal Muscle Excitation–Contraction Coupling

2007 ◽  
Vol 130 (4) ◽  
pp. 365-378 ◽  
Author(s):  
Sanjeewa A. Goonasekera ◽  
Nicole A. Beard ◽  
Linda Groom ◽  
Takashi Kimura ◽  
Alla D. Lyfenko ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Ryanodine Receptor ◽  
Calcium Release ◽  
Striated Muscle ◽  
Single Channel ◽  
Triple Mutant ◽  
Double Mutation ◽  
Excitation Contraction Coupling ◽  
Contraction Coupling ◽  
Functional Studies

Ca2+ release from intracellular stores is controlled by complex interactions between multiple proteins. Triadin is a transmembrane glycoprotein of the junctional sarcoplasmic reticulum of striated muscle that interacts with both calsequestrin and the type 1 ryanodine receptor (RyR1) to communicate changes in luminal Ca2+ to the release machinery. However, the potential impact of the triadin association with RyR1 in skeletal muscle excitation–contraction coupling remains elusive. Here we show that triadin binding to RyR1 is critically important for rapid Ca2+ release during excitation–contraction coupling. To assess the functional impact of the triadin-RyR1 interaction, we expressed RyR1 mutants in which one or more of three negatively charged residues (D4878, D4907, and E4908) in the terminal RyR1 intraluminal loop were mutated to alanines in RyR1-null (dyspedic) myotubes. Coimmunoprecipitation revealed that triadin, but not junctin, binding to RyR1 was abolished in the triple (D4878A/D4907A/E4908A) mutant and one of the double (D4907A/E4908A) mutants, partially reduced in the D4878A/D4907A double mutant, but not affected by either individual (D4878A, D4907A, E4908A) mutations or the D4878A/E4908A double mutation. Functional studies revealed that the rate of voltage- and ligand-gated SR Ca2+ release were reduced in proportion to the degree of interruption in triadin binding. Ryanodine binding, single channel recording, and calcium release experiments conducted on WT and triple mutant channels in the absence of triadin demonstrated that the luminal loop mutations do not directly alter RyR1 function. These findings demonstrate that junctin and triadin bind to different sites on RyR1 and that triadin plays an important role in ensuring rapid Ca2+ release during excitation–contraction coupling in skeletal muscle.

scholarly journals Interdomain Interactions within Ryanodine Receptors Regulate Ca2+ Spark Frequency in Skeletal Muscle

2001 ◽  
Vol 119 (1) ◽  
pp. 15-32 ◽  
Author(s):  
Alexander Shtifman ◽  
Christopher W. Ward ◽  
Takeshi Yamamoto ◽  
Jianli Wang ◽  
Beth Olbinski ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Lipid Bilayers ◽  
Laser Scanning ◽  
Muscle Fibers ◽  
Mammalian Skeletal Muscle ◽  
Open Probability ◽  
Release Channel ◽  
Pronounced Increase ◽  
Open Time ◽  
Interdomain Interactions

DP4 is a 36-residue synthetic peptide that corresponds to the Leu2442-Pro2477 region of RyR1 that contains the reported malignant hyperthermia (MH) mutation site. It has been proposed that DP4 disrupts the normal interdomain interactions that stabilize the closed state of the Ca2+ release channel (Yamamoto, T., R. El-Hayek, and N. Ikemoto. 2000. J. Biol. Chem. 275:11618–11625). We have investigated the effects of DP4 on local SR Ca2+ release events (Ca2+ sparks) in saponin-permeabilized frog skeletal muscle fibers using laser scanning confocal microscopy (line-scan mode, 2 ms/line), as well as the effects of DP4 on frog SR vesicles and frog single RyR Ca2+ release channels reconstituted in planar lipid bilayers. DP4 caused a significant increase in Ca2+ spark frequency in muscle fibers. However, the mean values of the amplitude, rise time, spatial half width, and temporal half duration of the Ca2+ sparks, as well as the distribution of these parameters, remained essentially unchanged in the presence of DP4. Thus, DP4 increased the opening rate, but not the open time of the RyR Ca2+ release channel(s) generating the sparks. DP4 also increased [3H]ryanodine binding to SR vesicles isolated from frog and mammalian skeletal muscle, and increased the open probability of frog RyR Ca2+ release channels reconstituted in bilayers, without changing the amplitude of the current through those channels. However, unlike in Ca2+ spark experiments, DP4 produced a pronounced increase in the open time of channels in bilayers. The same peptide with an Arg17 to Cys17 replacement (DP4mut), which corresponds to the Arg2458-to-Cys2458 mutation in MH, did not produce a significant effect on RyR activation in muscle fibers, bilayers, or SR vesicles. Mg2+ dependence experiments conducted with permeabilized muscle fibers indicate that DP4 preferentially binds to partially Mg2+-free RyR(s), thus promoting channel opening and production of Ca2+ sparks.

Abstract 950: Direct Evidence for an Important Role of Agonist-independent Constitutive I K,ACh Channel Activity in Atrial Tachycardia Remodeling

Circulation ◽  
2007 ◽  
Vol 116 (suppl_16) ◽  
Author(s):  
Niels Voigt ◽  
Ange Maguy ◽  
Yung-Hsin Yeh ◽  
Xiao-Yan Qi ◽  
Ursula Ravens ◽  
...  
Keyword(s):  
Atrial Tachycardia ◽  
Single Channel ◽  
Channel Activity ◽  
Open Probability ◽  
Direct Demonstration ◽  
Open Time ◽  
Therapy Target ◽  
Channel Properties ◽  
Constitutively Active

Background: Although atrial tachycardia (AT) appears to promote agonist-independent constitutively active I K,ACh that increases susceptibility to AF, direct demonstration of dysregulated I K,ACh channel function is lacking. We studied AT effects on single I K,ACh channel activity in dog atria. Methods: I K,ACh channel activity was recorded with cell-attached patch clamp in isolated atrial myocytes of control (CTL) and AT (7 days, 400 min −1 ) dogs. Results : AT prolonged inducible AF duration from 44±22 to 413±167 s; N=9 dogs/gp, P<0.001. In the absence of cholinergic stimulation, single-channel openings with typical I K,ACh conductance and rectification were observed in CTL and AT (Figure ). AT produced prominent agonist-independent I K,ACh activity due to 7-fold increased opening frequency (f o ) and 10-fold increased open probability (P o ) vs CTL (P<0.01 for each), but unaltered open time and single channel conductance. With maximum I K,ACh activation (10 μm carbachol, CCh), f o was 38% lower, open time constant 25% higher, and P o and unitary conductance unchanged for AT vs CTL. The selective Kir3 blocker tertiapin (100 nM) reduced f o and P o by 48% and 51% (P<0.05 each) without altering other channel properties, confirming the identity of I K,ACh. Conclusions : AT produces prominent agonist-independent constitutive single-channel I K,ACh activity, providing a molecular basis for previously-observed AT-enhanced macroscopic I K,ACh , as well as associated AP-shortening and tertiapin-suppressible AF promotion. These results suggest an important role for constitutively active I K,ACh channels in AT-remodeling and support their interest as a potential novel AF-therapy target.

Micromolar Ca2+ from sparks activates Ca2+-sensitive K+ channels in rat cerebral artery smooth muscle

2001 ◽  
Vol 281 (6) ◽  
pp. C1769-C1775 ◽  
Author(s):  
Guillermo J. Pérez ◽  
Adrian D. Bonev ◽  
Mark T. Nelson
Keyword(s):  
Smooth Muscle ◽  
Laser Scanning ◽  
Cerebral Arteries ◽  
Bk Channels ◽  
Bk Channel ◽  
Hill Coefficient ◽  
Channel Activity ◽  
Acetoxymethyl Ester ◽  
Open Probability ◽  
Apparent Dissociation Constant

The goal of the present study was to test the hypothesis that local Ca2+ release events (Ca2+ sparks) deliver high local Ca2+concentration to activate nearby Ca2+-sensitive K+ (BK) channels in the cell membrane of arterial smooth muscle cells. Ca2+ sparks and BK channels were examined in isolated myocytes from rat cerebral arteries with laser scanning confocal microscopy and patch-clamp techniques. BK channels had an apparent dissociation constant for Ca2+ of 19 μM and a Hill coefficient of 2.9 at −40 mV. At near-physiological intracellular Ca2+ concentration ([Ca2+]i; 100 nM) and membrane potential (−40 mV), the open probability of a single BK channel was low (1.2 × 10−6). A Ca2+spark increased BK channel activity to 18. Assuming that 1–100% of the BK channels are activated by a single Ca2+ spark, BK channel activity increases 6 × 105-fold to 6 × 103-fold, which corresponds to ∼30 μM to 4 μM spark Ca2+ concentration. 1,2-bis(2-aminophenoxy)ethane- N,N,N′,N′-tetraacetic acid acetoxymethyl ester caused the disappearance of all Ca2+sparks while leaving the transient BK currents unchanged. Our results support the idea that Ca2+ spark sites are in close proximity to the BK channels and that local [Ca2+]i reaches micromolar levels to activate BK channels.

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