scholarly journals Tracking Voltage-dependent Conformational Changes in Skeletal Muscle Sodium Channel during Activation

2002 ◽  
Vol 120 (5) ◽  
pp. 629-645 ◽  
Author(s):  
Baron Chanda ◽  
Francisco Bezanilla
Keyword(s):  
Skeletal Muscle ◽  
Sodium Channel ◽  
Slow Component ◽  
Fast Component ◽  
Lag Phase ◽  
Kinetic Properties ◽  
Charge Movement ◽  
Voltage Dependent ◽  
Domain Iii ◽  
Domain I

The primary voltage sensor of the sodium channel is comprised of four positively charged S4 segments that mainly differ in the number of charged residues and are expected to contribute differentially to the gating process. To understand their kinetic and steady-state behavior, the fluorescence signals from the sites proximal to each of the four S4 segments of a rat skeletal muscle sodium channel were monitored simultaneously with either gating or ionic currents. At least one of the kinetic components of fluorescence from every S4 segment correlates with movement of gating charge. The fast kinetic component of fluorescence from sites S216C (S4 domain I), S660C (S4 domain II), and L1115C (S4 domain III) is comparable to the fast component of gating currents. In contrast, the fast component of fluorescence from the site S1436C (S4 domain IV) correlates with the slow component of gating. In all the cases, the slow component of fluorescence does not have any apparent correlation with charge movement. The fluorescence signals from sites reflecting the movement of S4s in the first three domains initiate simultaneously, whereas the fluorescence signals from the site S1436C exhibit a lag phase. These results suggest that the voltage-dependent movement of S4 domain IV is a later step in the activation sequence. Analysis of equilibrium and kinetic properties of fluorescence over activation voltage range indicate that S4 domain III is likely to move at most hyperpolarized potentials, whereas the S4s in domain I and domain II move at more depolarized potentials. The kinetics of fluorescence changes from sites near S4-DIV are slower than the activation time constants, suggesting that the voltage-dependent movement of S4-DIV may not be a prerequisite for channel opening. These experiments allow us to map structural features onto the kinetic landscape of a sodium channel during activation.

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.

Primary structure of the adult human skeletal muscle voltage-dependent sodium channel

1992 ◽  
Vol 31 (2) ◽  
pp. 131-137 ◽  
Author(s):  
Alfred L. George ◽  
Jeffrey Komisarof ◽  
Roland G. Kallen ◽  
Robert L. Barchi
Keyword(s):  
Skeletal Muscle ◽  
Sodium Channel ◽  
Primary Structure ◽  
Human Skeletal Muscle ◽  
Adult Human ◽  
Voltage Dependent

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.

Activation heat and latency relaxation in relation to calcium movement in skeletal and cardiac muscle

1982 ◽  
Vol 60 (4) ◽  
pp. 529-541 ◽  
Author(s):  
Louis A. Mulieri ◽  
Norman R. Alpert
Keyword(s):  
Skeletal Muscle ◽  
Refractory Period ◽  
Muscle Activation ◽  
Slow Component ◽  
Isometric Force ◽  
Fast Component ◽  
Bathing Solution ◽  
Latency Relaxation ◽  
In Series ◽  
Activation Heat

Measurements of activation heat, initial heat, twitch tension, and latency relaxation were made using thin-layer, vacuum-deposited thermopiles and isometric force transducers, respectively. Experiments were performed on frog skeletal muscle fiber bundles and on rabbit right ventricular papillary muscles at 0, 15, and 21 °C in normal and 1.75× to 2.5× mannitol hyperosmotic bathing solutions. In skeletal muscle, activation heat, obtained by stretching to zero overlap, was only slightly affected by 1.75× hyperosmotic solution and consisted of a fast and a slow component. Both components have a refractory period and a relatively refractory period which can be demonstrated by double pulse stimulation. The twitch potentiators Zn2+ and caffeine increase the total activation heat and the magnitude and rate of the fast component. The temporal relation between the latency relaxation and activation heat is demonstrated. The latency relaxation is independent of the number of sarcomeres in series in a muscle. Activation heat and latency relaxation records from heart muscle are obtained in 2.5× hyperosmotic bathing solution. A model of excitation–contraction coupling is presented which indicates that (1) the downstroke of the latency relaxation monitors the functioning of the Ca2+ -permeability or debinding mechanism in the terminal cisternae, (2) the fast component of activation heat monitors the amount of Ca2+ bound to troponin C, and (3) the total amplitude of activation heat is a measure of the total quantity of Ca2+ cycled in a twitch.

scholarly journals Sodium channel gating currents in frog skeletal muscle.

1983 ◽  
Vol 82 (5) ◽  
pp. 679-701 ◽  
Author(s):  
D T Campbell
Keyword(s):  
Skeletal Muscle ◽  
Sodium Channel ◽  
Time Course ◽  
Channel Gating ◽  
Total Charge ◽  
Charge Movement ◽  
Frog Skeletal Muscle ◽  
Gating Currents ◽  
Gating Mechanism ◽  
Charge Movements

Charge movements similar to those attributed to the sodium channel gating mechanism in nerve have been measured in frog skeletal muscle using the vaseline-gap voltage-clamp technique. The time course of gating currents elicited by moderate to strong depolarizations could be well fitted by the sum of two exponentials. The gating charge exhibits immobilization: at a holding potential of -90 mV the proportion of charge that returns after a depolarizing prepulse (OFF charge) decreases with the duration of the prepulse with a time course similar to inactivation of sodium currents measured in the same fiber at the same potential. OFF charge movements elicited by a return to more negative holding potentials of -120 or -150 mV show distinct fast and slow phases. At these holding potentials the total charge moved during both phases of the gating current is equal to the ON charge moved during the preceding prepulse. It is suggested that the slow component of OFF charge movement represents the slower return of charge "immobilized" during the prepulse. A slow mechanism of charge immobilization is also evident: the maximum charge moved for a strong depolarization is approximately doubled by changing the holding potential from -90 to -150 mV. Although they are larger in magnitude for a -150-mV holding potential, the gating currents elicited by steps to a given potential have similar kinetics whether the holding potential is -90 or -150 mV.

Multiple components of voltage-dependent potassium current in normal rat anterior pituitary cells

1994 ◽  
Vol 72 (2) ◽  
pp. 719-729 ◽  
Author(s):  
J. Herrington ◽  
C. J. Lingle
Keyword(s):  
High Voltage ◽  
Anterior Pituitary ◽  
Slow Component ◽  
Fast Component ◽  
Pituitary Cells ◽  
Tail Current ◽  
Anterior Pituitary Cells ◽  
Voltage Dependent ◽  
Normal Rat ◽  
K Current

1. Voltage-dependent K+ currents were studied in normal rat anterior pituitary cells using the patch-clamp technique. To obtain cultures enriched for lactotrophs, density gradient centrifugation was performed on pituitary cells isolated from lactating rats. 2. Depolarizations to about -30 mV from a holding potential of -80 mV activate a rapidly inactivating [time constant (tau) approximately 15–20 ms at -20 mV]K+ current. This transient current activated at low voltages (termed IA) is abolished by 5 mM external 4-aminopyridine (4-AP) but is largely resistant to external tetraethylammonium (TEA) (< or = 30 mM). 3. Recovery from inactivation of IA is fast, with a tau of 100–200 ms at -80 mV. Deactivation is also fast (tau approximately 2.2 ms at -50 mV). The voltage of half-activation of IA is approximately -20 mV. The current is completely inactivated at a holding potential of -40 mV. 4. Voltage-dependent K+ current activated by depolarizations from a holding potential of -40 mV was first detectable at about -20 mV (high voltage-activated) and had a time course that varied among cells. 5. Deactivation of high voltage-activated K+ current was best described by the sum of two exponentials, with tau of about 3.7 and 30 ms at -50 mV. Both components reversed close to the equilibrium potential for K+. 6. The amplitudes of the two tail currents were independent of each other when variable-duration commands were used to activate current. The amplitude of the fast component was largest with 10- to 20-ms commands to +40 mV and was reduced (< or = 50%) with 136-ms commands. The slow component amplitude reached a peak by 40 ms and remained constant for commands < or = 136 ms at +40 mV. 7. The contribution of each component to the total high voltage-activated tail current was variable among cells, with the amount of fast component correlating with the amount of inactivation produced by commands to +40 mV. 8. The two components of tail current activated by depolarizations from the -40 mV holding potential were abolished by external TEA (10 mM). 4-AP (5 mM externally) selectively abolished the fast component of high voltage-activated tail current while only partially reducing the slow component. 9. These results suggest that normal rat anterior pituitary cells possess at least three distinct types of voltage-dependent K+ current: a low voltage-activated, transient current (IA) and two high voltage-activated currents.(ABSTRACT TRUNCATED AT 400 WORDS)

scholarly journals Dissociation of charge movement from calcium release and calcium current in skeletal myotubes by gabapentin

2002 ◽  
Vol 283 (3) ◽  
pp. C941-C949 ◽  
Author(s):  
Kris J. Alden ◽  
Jesús Garcı́a
Keyword(s):  
Skeletal Muscle ◽  
Calcium Current ◽  
Calcium Release ◽  
Maximum Amplitude ◽  
Charge Movement ◽  
Initial Voltage ◽  
Extra Charge ◽  
Voltage Dependent ◽  
Integral Role ◽  
Skeletal Myotubes

The skeletal muscle L-type calcium channel or dihydropyridine receptor (DHPR) plays an integral role in excitation-contraction (E-C) coupling. Its activation initiates three sequential events: charge movement (Qr), calcium release, and calcium current ( I Ca,L). This relationship suggests that changes in Qr might affect release and I Ca,L. Here we studied the effect of gabapentin (GBP) on the three events generated by DHPRs in skeletal myotubes in culture. GBP specifically binds to the α2/δ1 subunit of the brain and skeletal muscle DHPR. Myotubes were stimulated with a protocol that included a depolarizing prepulse to inactivate voltage-dependent proteins other than DHPRs. Gabapentin (50 μM) significantly increased Qr while decreasing the rate of rise of calcium transients. Gabapentin also reduced the maximum amplitude of the I Ca,L (as we previously reported) without modifying the kinetics of activation. Exposure of GBP-treated myotubes to 10 μM nifedipine prevented the increase of Qr promoted by this drug, indicating that the extra charge recorded originated from DHPRs. Our data suggest that GBP dissociates the functions of the DHPR from the initial voltage-sensing step and implicates a role for the α2/δ1 subunit in E-C coupling.

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