scholarly journals Voltage-induced Ca2+ release is supported by junctophilins 1, 2 and 3, and not by junctophilin 4

2021 ◽  
Vol 154 (9) ◽  
Author(s):  
Stefano Perni ◽  
Kurt G. Beam
Keyword(s):  
Skeletal Muscle ◽  
Conformational Changes ◽  
Knockout Mice ◽  
Calcium Release ◽  
Calcium Entry ◽  
Extracellular Calcium ◽  
Signaling Proteins ◽  
Potassium Depolarization ◽  
Complementary Approach ◽  
In Cells

In skeletal muscle, depolarization of the plasma membrane (PM) causes conformational changes of the calcium channel CaV1.1, which then activate RYR1 to release calcium from the sarcoplasmic reticulum (SR). Because it does not require extracellular calcium entry, this process is termed voltage-induced calcium release. In skeletal muscle, junctophilins (JPH) 1 and 2 are responsible for forming the SR–PM junctions at which voltage-induced calcium release occurs; structurally similar junctions with different molecular constituents are formed in neurons by JPH3 and JPH4. Studies on mice models demonstrated that JPH1 knockout mice can still perform voltage-induced calcium release, although the complementary approach to verify whether JPH1 alone also supports this release is not easily practicable due to the embryonic lethality of JPH2 knockout mice. In a previous work, we showed that voltage-induced calcium release could be recapitulated in HEK293-derived cells transfected with cDNAs for JPH2 and CaV1.1, β1a, Stac3, and RYR1. Here, we used this reconstitutional approach to test whether JPH1 and the more distantly related JPH3 and JPH4 can also support voltage-induced calcium release in HEK293-derived cells. Our data show that all the four isoforms colocalize with CaV1.1 at ER–PM junctions and that JPH1, JPH2, and JPH3, but not JPH4, cause colocalization of RYR1 with CaV1.1 at the junctions. To test for function, potassium depolarization was applied to cells in which WT CaV1.1 was replaced with the calcium impermeant mutant CaV1.1(N617D) to eliminate extracellular calcium entry. Calcium transients were observed in cells expressing JPH1, JPH2, and JPH3, indicating that these isoforms support voltage-induced calcium release, but not in cells expressing JPH4. Thus, the JPHs seem to act primarily to (1) form ER–PM junctions and (2) recruit the required set of signaling proteins to these junctions; voltage-induced calcium release can be supported by any JPH isoform fulfilling both of these functions.

Nitrendipine blocks high potassium contractures but not twitches in rat skeletal muscle

1988 ◽  
Vol 66 (9) ◽  
pp. 1210-1213 ◽  
Author(s):  
G. B. Frank ◽  
L. Konya ◽  
T. Subrahmanyam Sudha
Keyword(s):  
Skeletal Muscle ◽  
Calcium Ions ◽  
Calcium Uptake ◽  
Channel Blocker ◽  
Mechanical Response ◽  
Extracellular Calcium ◽  
The Other ◽  
Rat Skeletal Muscle ◽  
Potassium Depolarization ◽  
High Potassium

The effects of the organic calcium channel blocker nitrendipine was tested on electrically evoked twitches and on potassium depolarization-induced contractures of rat lumbricalis muscles. Nitrendipine (10−7 to 5 × 10−5 M) blocked only the potassium contractures. It was concluded that blocking calcium uptake through the slow voltage-senstitive calcium channels during potassium depolarization blocks the mechanical response of the muscle. Thus extracellular calcium ions are required for the excitation–contraction (E–C) coupling during depolarization contractures. On the other hand, electrically evoked twitches were not affected by nitrendipine; therefore, extracellular calcium ions entering via the slow voltage-sensitive channels are not required for E–C coupling during the twitch.

scholarly journals Enhanced extracellular calcium entry in skeletal muscle of malignant hyperthermia susceptible mice and humans

2019 ◽  
Vol 123 (4) ◽  
pp. e509
Author(s):  
Vikas Kaura ◽  
Jose R. López ◽  
Marie-Annie Shaw ◽  
Paul D. Allen ◽  
Philip M. Hopkins
Keyword(s):  
Skeletal Muscle ◽  
Malignant Hyperthermia ◽  
Calcium Entry ◽  
Extracellular Calcium ◽  
Malignant Hyperthermia Susceptible

Urea signaling to ERK phosphorylation in renal medullary cells requires extracellular calcium but not calcium entry

2001 ◽  
Vol 280 (1) ◽  
pp. F162-F171 ◽  
Author(s):  
Xiao-Yan Yang ◽  
Hongyu Zhao ◽  
Zheng Zhang ◽  
Karin D. Rodland ◽  
Jean-Baptiste Roullet ◽  
...  
Keyword(s):  
Intracellular Calcium ◽  
Calcium Release ◽  
Calcium Entry ◽  
Extracellular Calcium ◽  
Urea Treatment ◽  
Erk Activation ◽  
Calcium Dependent ◽  
Erk Phosphorylation ◽  
Extracellular Signal ◽  
A Cell

The renal cell line mIMCD3 exhibits markedly upregulated phosphorylation of the extracellular signal-regulated kinase (ERK) 1 and 2 in response to urea treatment (200 mM for 5 min). Previous data have suggested the involvement of a classical protein kinase C (cPKC)-dependent pathway in downstream events related to urea signaling. We now show that urea-inducible ERK activation requires extracellular calcium; unexpectedly, it occurs independently of activation of cPKC isoforms. Pharmacological inhibitors of known intracellular calcium release pathways and extracellular calcium entry pathways fail to inhibit ERK activation by urea. Fura 2 ratiometry was used to assess the effect of urea treatment on intracellular calcium mobilization. In single-cell analyses using subconfluent monolayers and in population-wide analyses using both confluent monolayers and cells in suspension, urea failed to increase intracellular calcium concentration. Taken together, these data indicate that urea-inducible ERK activation requires calcium action but not calcium entry. Although direct evidence is lacking, one possible explanation could include involvement of a calcium-dependent extracellular moiety of a cell surface-associated protein.

scholarly journals Measurement of shear stress-mediated intracellular calcium dynamics in human dermal lymphatic endothelial cells

2015 ◽  
Vol 308 (7) ◽  
pp. H697-H706 ◽  
Author(s):  
M. Jafarnejad ◽  
W. E. Cromer ◽  
R. R. Kaunas ◽  
S. L. Zhang ◽  
D. C. Zawieja ◽  
...  
Keyword(s):  
Endothelial Cells ◽  
Shear Stress ◽  
Intracellular Calcium ◽  
Calcium Release ◽  
Calcium Entry ◽  
Extracellular Calcium ◽  
Calcium Signal ◽  
Lymphatic Endothelial Cells ◽  
Crac Channels ◽  
Custom Made

The shear stress applied to lymphatic endothelial cells (LEC) by lymph flow changes dramatically under normal conditions as well as in response to disease conditions and immune reactions. In general, LEC are known to regulate the contraction frequency and strength of lymphatic pumping in response to shear stress. Intracellular calcium concentration ([Ca2+]i) is an important factor that regulates lymphatic contraction characteristics. In this study, we measured changes in the [Ca2+]i under different shear stress levels and determined the source of this calcium signal. Briefly, human dermal LEC were cultured in custom-made microchannels for 3 days before loading with 2 µM fura-2 AM, a ratiometric calcium dye to measure [Ca2+]i. Step changes in shear stress resulted in a rapid increase in [Ca2+]i followed by a gradual return to the basal level and sometimes below the initial baseline (45.2 ± 2.2 nM). The [Ca2+]i reached a peak at 126.2 ± 5.6 nM for 10 dyn/cm2 stimulus, whereas the peak was only 71.8 ± 5.4 nM for 1 dyn/cm2 stimulus, indicating that the calcium signal depends on the magnitude of shear stress. Removal of the extracellular calcium from the buffer or pharmocological blockade of calcium release-activated calcium (CRAC) channels significantly reduced the peak [Ca2+]i, demonstrating a role of extracellular calcium entry. Inhibition of endoplasmic reticulum (ER) calcium pumps showed the importance of intracellular calcium stores in the initiation of this signal. In conclusion, we demonstrated that the shear-mediated calcium signal is dependent on the magnitude of the shear and involves ER store calcium release and extracellular calcium entry.

scholarly journals Voltage sensor movements of CaV1.1 during an action potential in skeletal muscle fibers

2021 ◽  
Vol 154 (9) ◽  
Author(s):  
Quinton Banks ◽  
Hugo Bibollet ◽  
Minerva Contreras ◽  
Daniel F. Bennett ◽  
Roger A. Bannister ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Action Potential ◽  
Conformational Changes ◽  
Calcium Release ◽  
Muscle Fibers ◽  
Temporal Correlation ◽  
Voltage Sensor ◽  
Charge Movement ◽  
Voltage Gated ◽  
Extracellular Region

In excitation–contraction coupling (ECC), when the skeletal muscle action potential (AP) propagates into the transverse tubules, it modifies the conformational state of the voltage-gated calcium channels (CaV1.1). CaV1.1 serves as the voltage sensor for activation of calcium release from the sarcoplasmic reticulum (SR); however, many questions about this function persist. CaV1.1 α1 subunits contain four distinct homologous domains (I–IV). Each repeat includes six transmembranal helical segments; the voltage-sensing domain (VSD) is formed by S1–S4 segments, and the pore domain is formed by helices S5–S6. Because, in other voltage-gated channels, individual VSDs appear to be differentially involved in specific aspects of channel gating, here we thus hypothesized that not all the VSDs in CaV1.1 contribute equally to calcium-release activation. Yet, the voltage-sensor movements during an AP (the physiological stimulus for the muscle fiber) have not been previously measured in muscle. Reorientation of VSDs I–IV in CaV1.1 during an AP should generate a small but measurable electrical current. Still, neither the voltage-sensor charge movement during the AP nor the contribution of the individual VSDs to voltage-gated calcium release have been previously monitored. Here, we electrically monitor VSD movements using an AP voltage-clamp technique applied to muscle fibers. We introduce AP-fluorometry, a variant of the functional site-directed fluorescence, to track the movement of each VSD via a cysteine substitution on the extracellular region of S4 of each VSD and its labeling with a cysteine-reacting fluorescent probe, which served as an optical reporter of local rearrangements. Independent optical recordings of AP and calcium transients were performed to establish the temporal correlation between AP, AP-elicited charge movement, VSDs conformational changes, and calcium release flux. Our results support the hypothesis that not all VSDs in CaV1.1 contribute to ECC.

Store-operated calcium entry and increased endothelial cell permeability

2000 ◽  
Vol 279 (5) ◽  
pp. L815-L824 ◽  
Author(s):  
Natalie Norwood ◽  
Timothy M. Moore ◽  
David A. Dean ◽  
Rakesh Bhattacharjee ◽  
Ming Li ◽  
...  
Keyword(s):  
Endothelial Cell ◽  
Calcium Current ◽  
Calcium Release ◽  
Calcium Entry ◽  
Extracellular Calcium ◽  
Cell Permeability ◽  
Calcium Stores ◽  
Store Depletion ◽  
Endothelial Cell Permeability ◽  
Store Operated Calcium Entry

We hypothesized that myosin light chain kinase (MLCK) links calcium release to activation of store-operated calcium entry, which is important for control of the endothelial cell barrier. Acute inhibition of MLCK caused calcium release from inositol trisphosphate-sensitive calcium stores and prevented subsequent activation of store-operated calcium entry by thapsigargin, suggesting that MLCK serves as an important mechanism linking store depletion to activation of membrane calcium channels. Moreover, in voltage-clamped single rat pulmonary artery endothelial cells, thapsigargin activated an inward calcium current that was abolished by MLCK inhibition. F-actin disruption activated a calcium current, and F-actin stabilization eliminated the thapsigargin-induced current. Thapsigargin increased endothelial cell permeability in the presence, but not in the absence, of extracellular calcium, indicating the importance of calcium entry in decreasing barrier function. Although MLCK inhibition prevented thapsigargin from stimulating calcium entry, it did not prevent thapsigargin from increasing permeability. Rather, inhibition of MLCK activity increased permeability that was especially prominent in low extracellular calcium. In conclusion, MLCK links store depletion to activation of a store-operated calcium entry channel. However, inhibition of calcium entry by MLCK is not sufficient to prevent thapsigargin from increasing endothelial cell permeability.

scholarly journals Copper-induced activation of TRPs and VDCCs triggers a calcium signature response regulating gene expression in Ectocarpus siliculosus

PeerJ ◽  
2018 ◽  
Vol 6 ◽  
pp. e4556 ◽  
Author(s):  
Alberto González ◽  
Claudio A. Sáez ◽  
Alejandra Moenne
Keyword(s):  
Calcium Channels ◽  
Intracellular Calcium ◽  
Protein Kinases ◽  
Calcium Release ◽  
Trp Channels ◽  
Calcium Entry ◽  
Extracellular Calcium ◽  
Green Macroalgae ◽  
Ectocarpus Siliculosus ◽  
Intracellular Calcium Release

In certain multicellular photoautotrophs, such as plants and green macroalgae, it has been demonstrated that calcium signaling importantly mediates tolerance to copper excess. However, there is no information in brown macroalgae, which are phylogenetically distant from green algae and plants. We have previously shown that chronic copper levels (2.5 μM) activate transient receptor potential (TRP) channels in the model brown macroalga Ectocarpus siliculosus, allowing extracellular calcium entry at 13, 29, 39 and 51 min. Here, we showed that intracellular calcium increases also occurred at 3 and 5 h of exposure; these increases were inhibited by antagonists of voltage-dependent calcium channels (VDCCs); a chelating agent of extracellular calcium; an antagonist of endoplasmic reticulum (ER) ATPase; and antagonists of cADPR-, NAADP- and IP3-dependent calcium channels. Thus, copper activates VDCCs allowing extracellular calcium entry and intracellular calcium release from the ER via cADPR-, IP3- and NAADP-dependent channels. Furthermore, the level of transcripts encoding a phytochelatin synthase (PS) and a metallothionein (MT) were analyzed in the alga exposed to 2.5 μM copper from 3 to 24 h. The level of ps and mt transcripts increased until 24 h and these increases were inhibited by antagonists of calmodulins (CaMs), calcineurin B-like proteins (CBLs) and calcium-dependent protein kinases (CDPKs). Finally, activation of VDCC was inhibited by a mixture of TRP antagonists and by inhibitors of protein kinases. Thus, copper-mediated activation of TRPs triggers VDCCs via protein kinases, allowing extracellular calcium entry and intracellular calcium release from ER that, in turn, activate CaMs, CBLs and CDPKs increasing expression of PS and MT encoding genes in E. siliculosus.

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