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

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.

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

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.2026116118 ◽

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.

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The effect of temperature on charge movement repriming in amphibian skeletal muscle fibers

AJP Cell Physiology ◽

10.1152/ajpcell.1996.270.3.c892 ◽

1996 ◽

Vol 270 (3) ◽

pp. C892-C897 ◽

Cited By ~ 2

Author(s):

A. Gonzalez ◽

C. Caputo

Keyword(s):

Time Course ◽

Calcium Release ◽

Muscle Fibers ◽

High Energy ◽

Voltage Sensor ◽

Effect Of Temperature ◽

Potential Range ◽

Charge Movement ◽

Voltage Distribution ◽

Calcium Release Channel

Cut twitch muscle fibers, mounted in a triple Vaseline-gap chamber, were used to study the effects of temperature on intramembranous charge movement and, in particular, on the repriming of charge 1 (the intramembranous charge that normally moves in the potential range between -100 and +40 mV). Changing the holding potential from -90 to 0 mV modified the voltage distribution of charge movement but not the maximum movable charge. Temperature changes between 16 and 5 degrees C did not modify the fiber linear capacitance, the maximum nonlinear intramembranous charge, or the voltage distribution of charge 1 and charge 2 (the intramembranous charge moving in the membrane potential range between approximately -4 and -160 mV). We used a pulse protocol designed to study the repriming time course of charge 1, with little contamination from charge 2. The time course of charge movement repriming at 15 degrees C is described by a double exponential with time constants of 4.2 and 25 s. Repriming kinetics were found to be highly temperature dependent, with two rate-limiting steps having Q10 (increase in rate of a process by raising temperature 10 degrees C) values of 1.7 and 7.1 above and below 11.5 degrees C, respectively. This is characteristic of processes with a high energy of activation and could be associated with a conformational change of the voltage sensor or with the interaction between the voltage sensor and the calcium release channel.

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Action Potential-Evoked Calcium Release Is Impaired in Single Skeletal Muscle Fibers from Heart Failure Patients

PLoS ONE ◽

10.1371/journal.pone.0109309 ◽

2014 ◽

Vol 9 (10) ◽

pp. e109309 ◽

Cited By ~ 3

Author(s):

Marino DiFranco ◽

Marbella Quiñonez ◽

Perry Shieh ◽

Gregg C. Fonarow ◽

Daniel Cruz ◽

...

Keyword(s):

Heart Failure ◽

Skeletal Muscle ◽

Action Potential ◽

Calcium Release ◽

Muscle Fibers ◽

Heart Failure Patients ◽

Skeletal Muscle Fibers

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An allosteric model of the molecular interactions of excitation-contraction coupling in skeletal muscle.

The Journal of General Physiology ◽

10.1085/jgp.102.3.449 ◽

1993 ◽

Vol 102 (3) ◽

pp. 449-481 ◽

Cited By ~ 59

Author(s):

E Ríos ◽

M Karhanek ◽

J Ma ◽

A González

Keyword(s):

Skeletal Muscle ◽

Calcium Release ◽

Kinetic Equations ◽

Voltage Sensor ◽

Charge Movement ◽

Calcium Release Channel ◽

Open Probability ◽

Release Channel ◽

Voltage Sensors ◽

Function Relationship

A contact interaction is proposed to exist between the voltage sensor of the transverse tubular membrane of skeletal muscle and the calcium release channel of the sarcoplasmic reticulum. This interaction is given a quantitative formulation inspired in the Monod, Wyman, and Changeux model of allosteric transitions in hemoglobin (Monod, J., J. Wyman, and J.-P. Changeux. 1965. Journal of Molecular Biology. 12:88-118), and analogous to one proposed by Marks and Jones for voltage-dependent Ca channels (Marks, T. N., and S. W. Jones. 1992. Journal of General Physiology. 99:367-390). The allosteric protein is the calcium release channel, a homotetramer, with two accessible states, closed and open. The kinetics and equilibrium of this transition are modulated by voltage sensors (dihydropyridine receptors) pictured as four units per release channel, each undergoing independent voltage-driven transitions between two states (resting and activating). For each voltage sensor that moves to the activating state, the tendency of the channel to open increases by an equal (large) factor. The equilibrium and kinetic equations of the model are solved and shown to reproduce well a number of experimentally measured relationships including: charge movement (Q) vs. voltage, open probability of the release channel (Po) vs. voltage, the transfer function relationship Po vs. Q, and the kinetics of charge movement, release activation, and deactivation. The main consequence of the assumption of allosteric coupling is that primary effects on the release channel are transmitted backward to the voltage sensor and give secondary effects. Thus, the model reproduces well the effects of perchlorate, described in the two previous articles, under the assumption that the primary effect is to increase the intrinsic tendency of the release channel to open, with no direct effects on the voltage sensor. This modification of the open-closed equilibrium of the release channel causes a shift in the equilibrium dependency of charge movement with voltage. The paradoxical slowing of charge movement by perchlorate also results from reciprocal effects of the channel on the allosterically coupled voltage sensors. The observations of the previous articles plus the simulations in this article constitute functional evidence of allosteric transmission.

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Voltage-gated and calcium-gated calcium release during depolarization of skeletal muscle fibers

Biophysical Journal ◽

10.1016/s0006-3495(91)82120-8 ◽

1991 ◽

Vol 60 (4) ◽

pp. 867-873 ◽

Cited By ~ 58

Author(s):

V. Jacquemond ◽

L. Csernoch ◽

M.G. Klein ◽

M.F. Schneider

Keyword(s):

Skeletal Muscle ◽

Calcium Release ◽

Muscle Fibers ◽

Voltage Gated ◽

Skeletal Muscle Fibers

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Impaired calcium release during fatigue

Journal of Applied Physiology ◽

10.1152/japplphysiol.00908.2007 ◽

2008 ◽

Vol 104 (1) ◽

pp. 296-305 ◽

Cited By ~ 120

Author(s):

D. G. Allen ◽

G. D. Lamb ◽

H. Westerblad

Keyword(s):

Skeletal Muscle ◽

Sarcoplasmic Reticulum ◽

Action Potential ◽

Inorganic Phosphate ◽

Calcium Release ◽

Voltage Sensor ◽

Functional Importance ◽

Intracellular Atp ◽

Channel Opening ◽

Sensor Activation

Impaired calcium release from the sarcoplasmic reticulum (SR) has been identified as a contributor to fatigue in isolated skeletal muscle fibers. The functional importance of this phenomenon can be quantified by the use of agents, such as caffeine, which can increase SR Ca2+ release during fatigue. A number of possible mechanisms for impaired calcium release have been proposed. These include reduction in the amplitude of the action potential, potentially caused by extracellular K+ accumulation, which may reduce voltage sensor activation but is counteracted by a number of mechanisms in intact animals. Reduced effectiveness of SR Ca2+ channel opening is caused by the fall in intracellular ATP and the rise in Mg2+ concentrations that occur during fatigue. Reduced Ca2+ available for release within the SR can occur if inorganic phosphate enters the SR and precipitates with Ca2+. Further progress requires the development of methods that can identify impaired SR Ca2+ release in intact, blood-perfused muscles and that can distinguish between the various mechanisms proposed.

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S100A1 promotes action potential-initiated calcium release flux and force production in skeletal muscle

AJP Cell Physiology ◽

10.1152/ajpcell.00180.2010 ◽

2010 ◽

Vol 299 (5) ◽

pp. C891-C902 ◽

Cited By ~ 17

Author(s):

Benjamin L. Prosser ◽

Erick O. Hernández-Ochoa ◽

Richard M. Lovering ◽

Zoita Andronache ◽

Danna B. Zimmer ◽

...

Keyword(s):

Skeletal Muscle ◽

Action Potential ◽

Calcium Release ◽

Isometric Force ◽

Muscle Fibers ◽

Force Production ◽

Transport Processes ◽

Integrative Approach ◽

Release Flux

The role of S100A1 in skeletal muscle is just beginning to be elucidated. We have previously shown that skeletal muscle fibers from S100A1 knockout (KO) mice exhibit decreased action potential (AP)-evoked Ca2+ transients, and that S100A1 binds competitively with calmodulin to a canonical S100 binding sequence within the calmodulin-binding domain of the skeletal muscle ryanodine receptor. Using voltage clamped fibers, we found that Ca2+ release was suppressed at all test membrane potentials in S100A1−/− fibers. Here we examine the role of S100A1 during physiological AP-induced muscle activity, using an integrative approach spanning AP propagation to muscle force production. With the voltage-sensitive indicator di-8-aminonaphthylethenylpyridinium, we first demonstrate that the AP waveform is not altered in flexor digitorum brevis muscle fibers isolated from S100A1 KO mice. We then use a model for myoplasmic Ca2+ binding and transport processes to calculate sarcoplasmic reticulum Ca2+ release flux initiated by APs and demonstrate decreased release flux and greater inactivation of flux in KO fibers. Using in vivo stimulation of tibialis anterior muscles in anesthetized mice, we show that the maximal isometric force response to twitch and tetanic stimulation is decreased in S100A1−/− muscles. KO muscles also fatigue more rapidly upon repetitive stimulation than those of wild-type counterparts. We additionally show that fiber diameter, type, and expression of key excitation-contraction coupling proteins are unchanged in S100A1 KO muscle. We conclude that the absence of S100A1 suppresses physiological AP-induced Ca2+ release flux, resulting in impaired contractile activation and force production in skeletal muscle.

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A damped oscillation in the intramembranous charge movement and calcium release flux of frog skeletal muscle fibers.

The Journal of General Physiology ◽

10.1085/jgp.104.3.449 ◽

1994 ◽

Vol 104 (3) ◽

pp. 449-476 ◽

Cited By ~ 12

Author(s):

N Shirokova ◽

G Pizarro ◽

E Ríos

Keyword(s):

Skeletal Muscle ◽

Calcium Release ◽

Muscle Fibers ◽

Major Effect ◽

Charge Movement ◽

Frog Skeletal Muscle ◽

High Concentration ◽

Asymmetric Membrane ◽

Average Value ◽

Skeletal Muscle Fibers

Asymmetric membrane currents and calcium transients were recorded simultaneously from cut segments of frog skeletal muscle fibers voltage clamped in a double Vaseline-gap chamber in the presence of high concentration of EGTA intracellularly. An inward phase of asymmetric currents following the hump component was observed in all fibers during the depolarization pulse to selected voltages (congruent to -45 mV). The average value of the peak inward current was 0.1 A/F (SEM = 0.01, n = 18), and the time at which it occurred was 34 ms (SEM = 1.8, n = 18). A second delayed outward phase of asymmetric current was observed after the inward phase, in those experiments in which hump component and inward phase were large. It peaked at more variable time (between 60 and 130 ms) with amplitude 0.02 A/F (SEM = 0.003, n = 11). The transmembrane voltage during a pulse, measured with a glass microelectrode, reached its steady value in less than 10 ms and showed no oscillations. The potential was steady at the time when the delayed component of asymmetric current occurred. ON and OFF charge transfers were equal for all pulse durations. The inward phase moved 1.4 nC/microF charge (SEM = 0.8, n = 6), or about one third of the final value of charge mobilized by these small pulses, and the second outward phase moved 0.7 nC/microF (SEM = 0.8, n = 6), bringing back about half of the charge moved during the inward phase. When repolarization intersected the peak of the inward phase, the OFF charge transfer was independent of the repolarization voltage in the range -60 to -90 mV. When both pre- and post-pulse voltages were changed between -120 mV and -60 mV, the equality of ON and OFF transfers of charge persisted, although they changed from 113 to 81% of their value at -90 mV. The three delayed phases in asymmetric current were also observed in experiments in which the extracellular solution contained Cd2+, La3+ and no Ca2+. Large increases in intracellular [Cl-] were imposed, and had no major effect on the delayed components of the asymmetric current. The Ca2+ transients measured optically and the calculated Ca2+ release fluxes had three phases whenever a visible outward phase followed the inward phase in the asymmetric current. Several interventions intended to interfere with Ca release, reduced or eliminated the three delayed phases of the asymmetric current.(ABSTRACT TRUNCATED AT 400 WORDS)

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Calcium inactivation of calcium release in frog cut muscle fibers that contain millimolar EGTA or Fura-2.

The Journal of General Physiology ◽

10.1085/jgp.106.2.337 ◽

1995 ◽

Vol 106 (2) ◽

pp. 337-388 ◽

Cited By ~ 62

Author(s):

D S Jong ◽

P C Pape ◽

S M Baylor ◽

W K Chandler

Keyword(s):

Action Potential ◽

Voltage Clamp ◽

Time Constant ◽

Calcium Release ◽

Rana Temporaria ◽

Muscle Fibers ◽

Charge Movement ◽

Spatial Spread ◽

Fura 2 ◽

Peak Value

Cut muscle fibers from Rana temporaria (sarcomere length, 3.4-4.2 microns) were mounted in a double Vaseline-gap chamber (14-15 degrees C) and equilibrated with end-pool solutions that contained 20 mM EGTA and 1.76 mM Ca. Sarcoplasmic reticulum (SR) Ca release was estimated from changes in pH (Pape, P. C., D.-S. Jong, and W.K. Chandler. 1995. Journal of General Physiology. 106:000-000). Although the amplitude and duration of the [Ca] transient, as well as its spatial spread from the release sites, are reduced by EGTA, SR Ca release elicited by either depolarizing voltage-clamp pulses or action potentials behaved in a manner consistent with Ca inactivation of Ca release. After a step depolarization to -20 or 10 mV, the rate of SR Ca release, corrected for SR Ca depletion, reached a peak value within 5-15 ms and then rapidly decreased to a quasi-steady level that was about half the peak value; the time constant of the last half of the decrease was usually 2-4 ms. Immediately after an action potential or a 10-15 ms prepulse to -20 mV, the peak rate of SR Ca release elicited by a second stimulation, as well as the fractional amount of release, were substantially decreased. The rising phase of the rate of release was also reduced, suggesting that at least 0.9 of the ability of the SR to release Ca had been inactivated by the first stimulation. There was little change in intramembranous charge movement, suggesting that the changes in SR Ca release were not caused by changes in its voltage activation. These effects of a first stimulation on the rate of SR Ca release elicited by a second stimulation recovered during repolarization to -90 mV; the time constant of recovery was approximately 25 ms in the action-potential experiments and approximately 50 ms in the voltage-clamp experiments. Fura-2, which is able to bind Ca more rapidly than EGTA and hence reduce the amplitude of the [Ca] transient and its spatial spread from release sites by a greater amount, did not prevent Ca inactivation of Ca release, even at concentrations as large as 6-8 mM. These effects of Ca inactivation of Ca release can be simulated by the three-state, two-step model proposed by Schneider, M. F., and B. J. Simon (1988, Journal of Physiology. 405:727-745), in which SR Ca channels function as a single uniform population of channels. (ABSTRACT TRUNCATED AT 400 WORDS)

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