Effects of the halothane-sensitivity gene on sarcoplasmic reticulum function

1989 ◽  
Vol 257 (4) ◽  
pp. C787-C794 ◽  
Author(s):  
J. R. Mickelson ◽  
E. M. Gallant ◽  
W. E. Rempel ◽  
K. M. Johnson ◽  
L. A. Litterer ◽  
...  
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Calcium Release ◽  
Protein Product ◽  
Receptor Protein ◽  
Calcium Release Channel ◽  
Release Channel ◽  
Sr Calcium Release ◽  
Sensitivity Gene

Pigs heterozygous for the halothane-sensitivity gene exhibit a distinct phenotype with regard to both in vivo and in vitro muscle responses to halothane (E. M. Gallant, J. R. Mickelson, B. D. Roggow, S. K. Donaldson, C. F. Louis, and W. E. Rempel. Am. J. Physiol. 257 (Cell Physiol. 26): C781-C786, 1989). In this paper heavy sarcoplasmic reticulum (SR) preparations were isolated from the muscles of pigs of all three genotypes. The rate of calcium release from SR of pigs homozygous for the halothane-sensitivity gene was approximately twice that of SR from pigs homozygous for the normal allele. Furthermore, in the presence of 6 microM Ca2+, the binding of [3H]ryanodine to SR isolated from the homozygous halothane-sensitive pigs was of a higher affinity than was the binding to SR isolated from the homozygous normal pigs (Kd = 70-90 vs. 265 nM, respectively). The SR from pigs heterozygous for the halothane-sensitivity gene, however, demonstrated intermediate values for the rate of calcium release and the affinity for [3H]ryanodine (Kd = 192 nM). Thus the alterations in heavy SR calcium release and [3H]ryanodine binding in the pigs containing one copy of the halothane-sensitivity gene demonstrate a distinct heterozygote phenotype. These data also suggest that the protein product of this gene is closely associated with, and perhaps identical to, the SR calcium release channel-ryanodine receptor protein.

scholarly journals Calcium channel ITPR2 and mitochondria–ER contacts promote cellular senescence and aging

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Dorian V. Ziegler ◽  
David Vindrieux ◽  
Delphine Goehrig ◽  
Sara Jaber ◽  
Guillaume Collin ◽  
...  
Keyword(s):  
Cellular Senescence ◽  
Calcium Release ◽  
Liver Steatosis ◽  
Metabolic Stress ◽  
Calcium Release Channel ◽  
Release Channel ◽  
Age Related ◽  
Trisphosphate Receptor

AbstractCellular senescence is induced by stresses and results in a stable proliferation arrest accompanied by a pro-inflammatory secretome. Senescent cells accumulate during aging, promoting various age-related pathologies and limiting lifespan. The endoplasmic reticulum (ER) inositol 1,4,5-trisphosphate receptor, type 2 (ITPR2) calcium-release channel and calcium fluxes from the ER to the mitochondria are drivers of senescence in human cells. Here we show that Itpr2 knockout (KO) mice display improved aging such as increased lifespan, a better response to metabolic stress, less immunosenescence, as well as less liver steatosis and fibrosis. Cellular senescence, which is known to promote these alterations, is decreased in Itpr2 KO mice and Itpr2 KO embryo-derived cells. Interestingly, ablation of ITPR2 in vivo and in vitro decreases the number of contacts between the mitochondria and the ER and their forced contacts induce premature senescence. These findings shed light on the role of contacts and facilitated exchanges between the ER and the mitochondria through ITPR2 in regulating senescence and aging.

scholarly journals Modulation of the Frequency of Spontaneous Sarcoplasmic Reticulum Ca2+ Release Events (Ca2+ Sparks) by Myoplasmic [Mg2+] in Frog Skeletal Muscle

1998 ◽  
Vol 111 (2) ◽  
pp. 207-224 ◽  
Author(s):  
Alain Lacampagne ◽  
Michael G. Klein ◽  
Martin F. Schneider
Keyword(s):  
Skeletal Muscle ◽  
Sarcoplasmic Reticulum ◽  
Calcium Release ◽  
Frog Skeletal Muscle ◽  
Calcium Release Channel ◽  
Release Channel ◽  
Event Frequency ◽  
Open Time ◽  
Channel Opening ◽  
Sr Calcium Release

The modulation by internal free [Mg2+] of spontaneous calcium release events (Ca2+ “sparks”) from the sarcoplasmic reticulum (SR) was studied in depolarized notched frog skeletal muscle fibers using a laser scanning confocal microscope in line-scan mode (x vs. t). Over the range of [Mg2+] from 0.13 to 1.86 mM, decreasing the [Mg2+] induced an increase in the frequency of calcium release events in proportion to [Mg2+]−1.6. The change of event frequency was not due to changes in [Mg-ATP] or [ATP]. Analysis of individual SR calcium release event properties showed that the variation in event frequency induced by the change of [Mg2+] was not accompanied by any changes in the spatiotemporal spread (i.e., spatial half width or temporal half duration) of Ca2+ sparks. The increase in event frequency also had no effect on the distribution of event amplitudes. Finally, the rise time of calcium sparks was independent of the [Mg2+], indicating that the open time of the SR channel or channels underlying spontaneous calcium release events was not altered by [Mg2+] over the range tested. These results suggest that in resting skeletal fibers, [Mg2+] modulates the SR calcium release channel opening frequency by modifying the average closed time of the channel without altering the open time. A kinetic reaction scheme consistent with our results and those of bilayer and SR vesicle experiments indicates that physiological levels of resting Mg2+ may inhibit channel opening by occupying the site for calcium activation of the SR calcium release channel.

scholarly journals Thermal instability of rat muscle sarcoplasmic reticulum Ca2+-ATPase function

2002 ◽  
Vol 283 (4) ◽  
pp. E722-E728 ◽  
Author(s):  
J. D. Schertzer ◽  
H. J. Green ◽  
A. R. Tupling
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Atpase Activity ◽  
Thermal Instability ◽  
Calcium Release ◽  
Calcium Release Channel ◽  
Release Channel ◽  
Adult Rat ◽  
Hill Slope ◽  
Exercise Induced

To examine the thermal instability and the role of sulfhydryl (SH) oxidation on sarcoplasmic reticulum (SR) Ca2+-ATPase function, crude homogenates were prepared from the white portion of the gastrocnemius (WG) adult rat muscles ( n = 9) and incubated in vitro for ≤60 min either at a normal resting body temperature (37°C) or at a temperature indicative of exercise-induced hyperthermia (41°C) with DTT and without DTT (CON). In general, treatment with DTT resulted in higher Ca2+-ATPase and Ca2+ uptake values (nmol · mg protein−1 · min−1, P < 0.05), an effect that was not specific to time of incubation. Incubations at 41°C resulted in lower ( P< 0.05) Ca2+ uptake rates (156 ± 18 and 35.9 ± 3.3) compared with 37°C (570 ± 54 and 364 ± 26) at 30 and 60 min, respectively. At 37°C, ryanodine (300 μM), which was used to block Ca2+ release from the calcium release channel, prevented the time-dependent decrease in Ca2+ uptake. A general inactivation ( P < 0.05) of maximal Ca2+-ATPase activity ( V max) in CON was observed with incubation time (0 > 30 > 60 min), with the effect being more pronounced ( P < 0.05) at 41°C compared with 37°C. The Hill slope, a measure of co-operativity, and the pCa50, the cytosolic Ca2+ concentration required for half-maximal activation of Ca2+-ATPase activity, decreased ( P < 0.05) at 41°C only. Treatment with DTT attenuated the alterations in enzyme kinetics. The increase in V max with the Ca2+ionophore A-23187 was less pronounced at 41°C compared with 37°C. It is concluded that exposure of homogenates to a temperature typically experienced in exercise results in a reduction in the coupling ratio, which is mediated primarily by lower Ca2+ uptake and occurs as a result of increases in membrane permeability to Ca2+. Moreover, the decreases in Ca2+-ATPase kinetics in WG with sustained heat stress result from SH oxidation.

scholarly journals Triad formation: organization and function of the sarcoplasmic reticulum calcium release channel and triadin in normal and dysgenic muscle in vitro.

1993 ◽  
Vol 123 (5) ◽  
pp. 1161-1174 ◽  
Author(s):  
B E Flucher ◽  
S B Andrews ◽  
S Fleischer ◽  
A R Marks ◽  
A Caswell ◽  
...  
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Calcium Release ◽  
Calcium Transients ◽  
Molecular Organization ◽  
Calcium Release Channel ◽  
Release Channel ◽  
Calcium Indicators ◽  
Immunofluorescence Labeling ◽  
And Function

Excitation-contraction (E-C) coupling is thought to involve close interactions between the calcium release channel (ryanodine receptor; RyR) of the sarcoplasmic reticulum (SR) and the dihydropyridine receptor (DHPR) alpha 1 subunit in the T-tubule membrane. Triadin, a 95-kD protein isolated from heavy SR, binds both the RyR and DHPR and may thus participate in E-C coupling or in interactions responsible for the formation of SR/T-tubule junctions. Immunofluorescence labeling of normal mouse myotubes shows that the RyR and triadin co-aggregate with the DHPR in punctate clusters upon formation of functional junctions. Dysgenic myotubes with a deficiency in the alpha 1 subunit of the DHPR show reduced expression and clustering of RyR and triadin; however, both proteins are still capable of forming clusters and attaining mature cross-striated distributions. Thus, the molecular organization of the RyR and triadin in the terminal cisternae of SR as well as its association with the T-tubules are independent of interactions with the DHPR alpha 1 subunit. Analysis of calcium transients in dysgenic myotubes with fluorescent calcium indicators reveals spontaneous and caffeine-induced calcium release from intracellular stores similar to those of normal muscle; however, depolarization-induced calcium release is absent. Thus, characteristic calcium release properties of the RyR do not require interactions with the DHPR; neither do they require the normal organization of the RyR in the terminal SR cisternae. In hybrids of dysgenic myotubes fused with normal cells, both action potential-induced calcium transients and the normal clustered organization of the RyR are restored in regions expressing the DHPR alpha 1 subunit.

Inositol 1,4,5-trisphosphate releases intracellular Ca2+ in permeabilized chick atria

1990 ◽  
Vol 258 (6) ◽  
pp. H1745-H1752 ◽  
Author(s):  
A. M. Vites ◽  
A. Pappano
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Calcium Release ◽  
Induced Response ◽  
Calcium Release Channel ◽  
Release Channel ◽  
Loading Cycle ◽  
Maximum Tension ◽  
Atrial Muscle ◽  
Inositol 1,4,5 Trisphosphate ◽  
Sr Calcium Release

Inositol 1,4,5-trisphosphate (IP3) and caffeine evoked transient, reversible, and concentration-dependent increases in tension in saponin-treated chick atrial muscle. Contractures evoked by IP3 and caffeine were detected in solutions with 70 microM EGTA at pCa 7.0. In the presence of 7 mM EGTA, neither IP3 nor caffeine was able to evoke a contracture. Maximally effective concentrations of IP3 (20 microM) and caffeine (20 mM) developed tensions to approximately 44 and 83% of that elicited by pCa 5.0 (maximum tension = 100%), respectively. The IP3- or caffeine-induced contractures were consistently reproduced when the sarcoplasmic reticulum (SR) had previously been loaded with calcium. Preexposure to caffeine suppressed the following IP3-induced response. When ryanodine (1-10 microM) was present throughout the SR-loading cycle, the responses to IP3 and caffeine were prevented. However, when ryanodine was added after the SR was loaded with calcium, neither the response to IP3 nor that to caffeine was affected. These results are consistent with the hypothesis that ryanodine inhibition requires prior activation of the SR calcium-release channel. It is concluded that both IP3 and caffeine increased tension in the SR by releasing calcium from it. The effect of IP3 is consistent with its messenger role as a calcium-mobilizing agent.

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