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

2021 ◽  
Vol 118 (40) ◽  
pp. e2026116118
Author(s):  
Quinton Banks ◽  
Hugo Bibollet ◽  
Minerva Contreras ◽  
Daniel F. Bennett ◽  
Roger A. Bannister ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Action Potential ◽  
Muscle Fibers ◽  
Voltage Sensor ◽  
Fluorescence Signal ◽  
Charge Movement ◽  
Electrical Measurements ◽  
Voltage Sensing ◽  
Skeletal Muscle Fibers

The skeletal muscle L-type Ca2+ channel (CaV1.1) works primarily as a voltage sensor for skeletal muscle action potential (AP)-evoked Ca2+ release. CaV1.1 contains four distinct voltage-sensing domains (VSDs), yet the contribution of each VSD to AP-evoked Ca2+ release remains unknown. To investigate the role of VSDs in excitation–contraction coupling (ECC), we encoded cysteine substitutions on each S4 voltage-sensing segment of CaV1.1, expressed each construct via in vivo gene transfer electroporation, and used in cellulo AP fluorometry to track the movement of each CaV1.1 VSD in skeletal muscle fibers. We first provide electrical measurements of CaV1.1 voltage sensor charge movement in response to an AP waveform. Then we characterize the fluorescently labeled channels’ VSD fluorescence signal responses to an AP and compare them with the waveforms of the electrically measured charge movement, the optically measured free myoplasmic Ca2+, and the calculated rate of Ca2+ release from the sarcoplasmic reticulum for an AP, the physiological signal for skeletal muscle fiber activation. A considerable fraction of the fluorescence signal for each VSD occurred after the time of peak Ca2+ release, and even more occurred after the earlier peak of electrically measured charge movement during an AP, and thus could not directly reflect activation of Ca2+ release or charge movement, respectively. However, a sizable fraction of the fluorometric signals for VSDs I, II, and IV, but not VSDIII, overlap the rising phase of charge moved, and even more for Ca2+ release, and thus could be involved in voltage sensor rearrangements or Ca2+ release activation.

The Collapse of the Sarcoplasmic Reticulum in Skeletal Muscle

1978 ◽  
Vol 33 (7-8) ◽  
pp. 561-573 ◽  
Author(s):  
Joachim R. Sommer ◽  
Nancy R. Wallace ◽  
Wilhelm Hasselbach
Keyword(s):  
Skeletal Muscle ◽  
Sarcoplasmic Reticulum ◽  
Action Potential ◽  
Muscle Fibers ◽  
Membrane Capacitance ◽  
Frog Skeletal Muscle ◽  
Skeletal Muscle Fibers ◽  
Plausible Mechanism

Abstract When various cations, including Ca2+, are in the fixative, both sarcoplasmic reticulum (SR) of whole skeletal muscle and isolated SR vesicles collapse to form pentalaminate “compound membranes” that result from the apparent fusion of the lumenal lamellae of the membranous envelope of the SR. The process may be reversed by subsequently soaking the tissue in 1 ᴍ NaCl. An identical morphological phenomenon is observed in unfixed quickly frozen isolated frog skeletal muscle fibers, the cation in that case coming from endogenous sources. The hypothesis is advanced that the collapse is an in vivo process mediated by the sequestration of Ca2+ after contraction. The resulting obliteration of the SR lumen would have the effect of displacing the SR contents into the junctional SR, as well as electrically isolating the free SR from the junctional SR during relaxation. As a consequence, resistive coupling between the plasmalemma and the junctional SR becomes a plausible mechanism for the translation of the action potential into Ca2+ release, since the bulk of the SR membrane capacitance would now remain separated from the plasmalemma during relaxation.

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.

scholarly journals Defective Acetylcholine Receptor Subunit Switch Precedes Atrophy of Slow-Twitch Skeletal Muscle Fibers Lacking ERK1/2 Kinases in Soleus Muscle

2016 ◽  
Vol 6 (1) ◽  
Author(s):  
Shuo Wang ◽  
Bonnie Seaberg ◽  
Ximena Paez-Colasante ◽  
Mendell Rimer
Keyword(s):  
Skeletal Muscle ◽  
Acetylcholine Receptor ◽  
Soleus Muscle ◽  
Muscle Fibers ◽  
Neuromuscular Synapse ◽  
Fiber Morphology ◽  
Skeletal Muscle Fibers ◽  
Slow Twitch

Abstract To test the role of extracellular-signal regulated kinases 1 and 2 (ERK1/2) in slow-twitch, type 1 skeletal muscle fibers, we studied the soleus muscle in mice genetically deficient for myofiber ERK1/2. Young adult mutant soleus was drastically wasted, with highly atrophied type 1 fibers, denervation at most synaptic sites, induction of “fetal” acetylcholine receptor gamma subunit (AChRγ), reduction of “adult” AChRε, and impaired mitochondrial biogenesis and function. In weanlings, fiber morphology and mitochondrial markers were mostly normal, yet AChRγ upregulation and AChRε downregulation were observed. Synaptic sites with fetal AChRs in weanling muscle were ~3% in control and ~40% in mutants, with most of the latter on type 1 fibers. These results suggest that: (1) ERK1/2 are critical for slow-twitch fiber growth; (2) a defective γ/ε-AChR subunit switch, preferentially at synapses on slow fibers, precedes wasting of mutant soleus; (3) denervation is likely to drive this wasting, and (4) the neuromuscular synapse is a primary subcellular target for muscle ERK1/2 function in vivo.

scholarly journals Anatomical distribution of voltage-dependent membrane capacitance in frog skeletal muscle fibers.

1989 ◽  
Vol 93 (3) ◽  
pp. 565-584 ◽  
Author(s):  
C L Huang ◽  
L D Peachey
Keyword(s):  
Skeletal Muscle ◽  
Muscle Fibers ◽  
Fiber Surface ◽  
Membrane Capacitance ◽  
Hypertonic Solution ◽  
Charge Movement ◽  
Frog Skeletal Muscle ◽  
Transverse Tubule ◽  
Skeletal Muscle Fibers ◽  
Voltage Dependent

Components of nonlinear capacitance, or charge movement, were localized in the membranes of frog skeletal muscle fibers by studying the effect of 'detubulation' resulting from sudden withdrawal of glycerol from a glycerol-hypertonic solution in which the muscles had been immersed. Linear capacitance was evaluated from the integral of the transient current elicited by imposed voltage clamp steps near the holding potential using bathing solutions that minimized tubular voltage attenuation. The dependence of linear membrane capacitance on fiber diameter in intact fibers was consistent with surface and tubular capacitances and a term attributable to the capacitance of the fiber end. A reduction in this dependence in detubulated fibers suggested that sudden glycerol withdrawal isolated between 75 and 100% of the transverse tubules from the fiber surface. Glycerol withdrawal in two stages did not cause appreciable detubulation. Such glycerol-treated but not detubulated fibers were used as controls. Detubulation reduced delayed (q gamma) charging currents to an extent not explicable simply in terms of tubular conduction delays. Nonlinear membrane capacitance measured at different voltages was expressed normalized to accessible linear fiber membrane capacitance. In control fibers it was strongly voltage dependent. Both the magnitude and steepness of the function were markedly reduced by adding tetracaine, which removed a component in agreement with earlier reports for q gamma charge. In contrast, detubulated fibers had nonlinear capacitances resembling those of q beta charge, and were not affected by adding tetracaine. These findings are discussed in terms of a preferential localization of tetracaine-sensitive (q gamma) charge in transverse tubule membrane, in contrast to a more even distribution of the tetracaine-resistant (q beta) charge in both transverse tubule and surface membranes. These results suggest that q beta and q gamma are due to different molecules and that the movement of q gamma in the transverse tubule membrane is the voltage-sensing step in excitation-contraction coupling.

Ischemia/reperfusion-induced changes in intracellular free Ca2+ levels in rat skeletal muscle fibers – an in vivo study

2000 ◽  
Vol 440 (2) ◽  
pp. 302-308 ◽  
Author(s):  
Tamás Ivanics ◽  
Zsuzsa Miklós ◽  
Zoltán Ruttner ◽  
Sándor Bátkai ◽  
Dick W. Slaaf ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Ischemia Reperfusion ◽  
Muscle Fibers ◽  
In Vivo Study ◽  
Rat Skeletal Muscle ◽  
Skeletal Muscle Fibers ◽  
Induced Changes

scholarly journals Kinetic properties of intramembrane charge movement under depolarized conditions in frog skeletal muscle fibers.

1991 ◽  
Vol 98 (2) ◽  
pp. 365-378 ◽  
Author(s):  
G Szücs ◽  
Z Papp ◽  
L Csernoch ◽  
L Kovács
Keyword(s):  
Skeletal Muscle ◽  
Voltage Dependence ◽  
Slow Component ◽  
Muscle Fibers ◽  
Ionic Current ◽  
Kinetic Properties ◽  
Constant Field ◽  
Charge Movement ◽  
Skeletal Muscle Fibers ◽  
Intramembrane Charge Movement

Intramembrane charge movement was measured on skeletal muscle fibers of the frog in a single Vaseline-gap voltage clamp. Charge movements determined both under polarized conditions (holding potential, VH = -100 mV; Qmax = 30.4 +/- 4.7 nC/micro(F), V = -44.4 mV, k = 14.1 mV; charge 1) and in depolarized states (VH = 0 mV; Qmax = 50.0 +/- 6.7 nC/micro(F), V = -109.1 mV, k = 26.6 mV; charge 2) had properties as reported earlier. Linear capacitance (LC) of the polarized fibers was increased by 8.8 +/- 4.0% compared with that of the depolarized fibers. Using control pulses measured under depolarized conditions to calculate charge 1, a minor change in the voltage dependence (to V = -44.6 mV and k = 14.5 mV) and a small increase in the maximal charge (to Qmax = 31.4 +/- 5.5 nC/micro(F] were observed. While in most cases charge 1 transients seemed to decay with a single exponential time course, charge 2 currents showed a characteristic biexponential behavior at membrane potentials between -90 and -180 mV. The voltage dependence of the rate constant of the slower component was fitted with a simple constant field diffusion model (alpha m = 28.7 s-1, V = -124.0 mV, and k = 15.6 mV). The midpoint voltage (V) was similar to that obtained from the Q-V fit of charge 2, while the steepness factor (k) resembled that of charge 1. This slow component could also be isolated using a stepped OFF protocol; that is, by hyperpolarizing the membrane to -190 mV for 200 ms and then coming back to 0 mV in two steps. The faster component was identified as an ionic current insensitive to 20 mM Co2+ but blocked by large hyperpolarizing pulses. These findings are consistent with the model implying that charge 1 and the slower component of charge 2 interconvert when the holding potential is changed. They also explain the difference previously found when comparing the steepness factors of the voltage dependence of charge 1 and charge 2.

scholarly journals In Vivo Fatigue Reduces In Vitro Performance In Human Skeletal Muscle Fibers

2021 ◽  
Vol 53 (8S) ◽  
pp. 110-111
Author(s):  
Austin W. Ricci ◽  
Scott J. Mongold ◽  
Grace E. Privett ◽  
Karen W. Needham ◽  
Damien M. Callahan
Keyword(s):  
Skeletal Muscle ◽  
Human Skeletal Muscle ◽  
Muscle Fibers ◽  
Skeletal Muscle Fibers ◽  
In Vitro Performance

scholarly journals Effects of dihydropyridine receptor II-III loop peptides on Ca2+ release in skinned skeletal muscle fibers

2000 ◽  
Vol 279 (4) ◽  
pp. C891-C905 ◽  
Author(s):  
Graham D. Lamb ◽  
Roque El-Hayek ◽  
Noriaki Ikemoto ◽  
D. George Stephenson
Keyword(s):  
Skeletal Muscle ◽  
Direct Action ◽  
Muscle Fibers ◽  
Dihydropyridine Receptor ◽  
Intracellular Loop ◽  
Release Channel ◽  
Voltage Sensors ◽  
Skeletal Muscle Fibers ◽  
Peptide Segments

In skeletal muscle fibers, the intracellular loop between domains II and III of the α1-subunit of the dihydropyridine receptor (DHPR) may directly activate the adjacent Ca2+ release channel in the sarcoplasmic reticulum. We examined the effects of synthetic peptide segments of this loop on Ca2+ release in mechanically skinned skeletal muscle fibers with functional excitation-contraction coupling. In rat fibers at physiological Mg2+ concentration ([Mg2+]; 1 mM), a 20-residue skeletal muscle DHPR peptide [AS(20); Thr671-Leu690; 30 μM], shown previously to induce Ca2+ release in a triad preparation, caused only small spontaneous force responses in ∼40% of fibers, although it potentiated responses to depolarization and caffeine in all fibers. The COOH-terminal half of AS(20)[AS(10)] induced much larger spontaneous responses but also caused substantial inhibition of Ca2+release to both depolarization and caffeine. Both peptides induced or potentiated Ca2+ release even when the voltage sensors were inactivated, indicating direct action on the Ca2+ release channels. The corresponding 20-residue cardiac DHPR peptide [AC(20); Thr793-Ala812] was ineffective, but its COOH-terminal half [AC(10)] had effects similar to AS(20). In the presence of lower [Mg2+] (0.2 mM), exposure to either AS(20) or AC(10) (30 μM) induced substantial Ca2+ release. Peptide CS (100 μM), a loop segment reported to inhibit Ca2+ release in triads, caused partial inhibition of depolarization-induced Ca2+ release. In toad fibers, each of the A peptides had effects similar to or greater than those in rat fibers. These findings suggest that the A and C regions of the skeletal DHPR II-III loop may have important roles in vivo.

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