scholarly journals Effects of Caffeine on Crayfish Muscle Fibers

1970 ◽  
Vol 55 (5) ◽  
pp. 665-687 ◽  
Author(s):  
Dante J. Chiarandini ◽  
John P. Reuben ◽  
Lucien Girardier ◽  
George M. Katz ◽  
Harry Grundfest
Keyword(s):  
Muscle Fibers ◽  
Bathing Medium ◽  
Contractile Responses ◽  
Crayfish Muscle ◽  
Contractile System ◽  
Mn Recovery

When caffeine evokes a contraction, and only then, crayfish muscle fibers become refractory to a second challenge with caffeine for up to 20 min in the standard saline (5 mM Ko). However, the fibers still respond with contraction to an increase in Ko, though with diminished tension. Addition of Mn slows recovery, but the latter is greatly accelerated during exposure of the fiber to high Ko, or after a brief challenge with high Ko. Neither the depolarization induced by the K, nor the repolarization after its removal accounts for the acceleration, which occurs only if the challenge with K had itself activated the contractile system; acceleration is blocked when contractile responses to K are blocked by reducing the Ca in the bath or by adding Mn. Recovery is accelerated by redistribution of intracellular Cl and by trains of intracellularly applied depolarizing pulses, but not by hyperpolarization. The findings indicate that two sources of Ca can be mobilized to activate the contractile system. Caffeine mobilizes principally the Ca store of the SR. Depolarizations that are induced by high Ko, by transient efflux of Cl, or by intracellularly applied currents mobilize another source of Ca which is strongly dependent upon the entry of Ca from the bathing medium. The sequestering mechanism of the SR apparently can utilize this second source of Ca to replenish its own store so as to accelerate recovery of responsiveness to a new challenge with caffeine.

scholarly journals Effect of electromagnetic field GSM on contractile responses of fast‐twitch intact skeletal muscle fibers

2011 ◽  
Vol 25 (S1) ◽  
Author(s):  
Wiam Ramadan ◽  
Hanane Akhdar ◽  
Fatima Jebai ◽  
Yolla Makhour ◽  
Dana Zeyneddine ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Electromagnetic Field ◽  
Muscle Fibers ◽  
Contractile Responses ◽  
Skeletal Muscle Fibers ◽  
Fast Twitch

Effects of BAPTA on force and Ca2+ transient during isometric contraction of frog muscle fibers

1998 ◽  
Vol 275 (2) ◽  
pp. C375-C381 ◽  
Author(s):  
Y.-B. Sun ◽  
C. Caputo ◽  
K. A. P. Edman
Keyword(s):  
Mechanical Performance ◽  
Muscle Fibers ◽  
Frog Muscle ◽  
Clear Correlation ◽  
Bathing Solution ◽  
Control Value ◽  
Contractile System ◽  
Intracellular Ca ◽  
Cross Bridges ◽  
Reduced State

The effects of 1,2-bis(2-aminophenoxy)ethane- N, N, N′, N′-tetraacetic acid (BAPTA) on force and intracellular Ca2+ transient were studied during isometric twitches and tetanuses in single frog muscle fibers. BAPTA was added to the bathing solution in its permeant AM form (50 and 100 μM). There was no clear correlation between the changes in force and the changes in Ca2+ transient. Thus during twitch stimulation BAPTA did not suppress the Ca2+ transient until the force had been reduced to <50% of its control value. At the same time, the peak myoplasmic free Ca2+concentration reached during tetanic stimulation was markedly increased, whereas the force was slightly reduced by BAPTA. The effects of BAPTA were not duplicated by using another Ca2+ chelator, EGTA, indicating that BAPTA may act differently as a Ca2+ chelator. Stiffness measurements suggest that the decrease in mechanical performance in the presence of BAPTA is attributable to a reduced number of active cross bridges. The results could mean that BAPTA, under the conditions used, inhibits the binding of Ca2+ to troponin C resulting in a reduced state of activation of the contractile system.

Fast BK-Type Channel Mediates the Ca2+-Activated K+ Current in Crayfish Muscle

1999 ◽  
Vol 82 (4) ◽  
pp. 1655-1661 ◽  
Author(s):  
Alfonso Araque ◽  
Washington Buño
Keyword(s):  
Electrical Activity ◽  
Single Channel ◽  
Muscle Fibers ◽  
Ionic Channels ◽  
Bk Channels ◽  
Intrinsic Properties ◽  
Open Probability ◽  
Crayfish Muscle ◽  
Fast Activation ◽  
Inside Out

The role of the Ca2+-activated K+ current ( I K(Ca)) in crayfish opener muscle fibers is functionally important because it regulates the graded electrical activity that is characteristic of these fibers. Using the cell-attached and inside-out configurations of the patch-clamp technique, we found three different classes of channels with properties that matched those expected of the three different ionic channels mediating the depolarization-activated macroscopic currents previously described (Ca2+, K+, and Ca2+-dependent K+ currents). We investigated the properties of the ionic channels mediating the extremely fast activating and persistent I K(Ca). These voltage- and Ca2+-activated channels had a mean single-channel conductance of ∼ 70 pS and showed a very fast activation. Both the single-channel open probability and the speed of activation increased with depolarization. Both parameters also increased in inside-out patches, i.e., in high Ca2+concentration. Intracellular loading with the Ca2+ chelator bis(2-aminophenoxy) ethane- N, N,N′,N′-tetraacetic acid gradually reduced and eventually prevented channel openings. The channels opened at very brief delays after the pulse depolarization onset (<5 ms), and the time-dependent open probability was constant during sustained depolarization (≤560 ms), matching both the extremely fast activation kinetics and the persistent nature of the macroscopic I K(Ca). However, the intrinsic properties of these single channels do not account for the partial apparent inactivation of the macroscopic I K(Ca), which probably reflects temporal Ca2+ variations in the whole muscle fiber. We conclude that the channels mediating I K(Ca) in crayfish muscle are voltage- and Ca2+-gated BK channels with relatively small conductance. The intrinsic properties of these channels allow them to act as precise Ca2+ sensors that supply the exact feedback current needed to control the graded electrical activity and therefore the contraction of opener muscle fibers.

scholarly journals The Role of Sodium Current in the Radial Spread of Contraction in Frog Muscle Fibers

1970 ◽  
Vol 55 (6) ◽  
pp. 703-715 ◽  
Author(s):  
L. L. Costantin
Keyword(s):  
Muscle Fiber ◽  
Sodium Current ◽  
Muscle Fibers ◽  
Fiber Surface ◽  
Sodium Concentration ◽  
Entire Cross Section ◽  
Bathing Medium ◽  
Radial Extent ◽  
Radial Spread

The membrane potential of isolated muscle fibers was controlled with a two-electrode voltage clamp, and the radial extent of contraction elicited by depolarizing pulses of increasing magnitude was observed microscopically. Depolarizations of the fiber surface only 1–2 mv greater than the contraction threshold produced shortening throughout the entire cross-section of the muscle fiber. The radial spread of contraction was less effective in fibers exposed to tetrodotoxin or to a bathing medium with a greatly reduced sodium concentration. The results provide evidence that depolarization of a muscle fiber produces an increase in sodium conductance in the T tubule membrane and that the resultant sodium current contributes to the spread of depolarization along the T system.

scholarly journals Dual effect of L-glutamate on excitatory postjunctional membranes of crayfish muscle.

1975 ◽  
Vol 65 (5) ◽  
pp. 677-691 ◽  
Author(s):  
P S Taraskevich
Keyword(s):  
Muscle Fibers ◽  
Reversal Potential ◽  
Dual Effect ◽  
Sodium Conductance ◽  
Crayfish Muscle ◽  
Permeability Changes ◽  
Extracellular Sodium ◽  
Sodium And Potassium

Iontophoretically applied glutamate produces different excitatory postjunctional permeability changes on separate muscle fibers in a single crayfish muslce. At junctions on some fibers glutamate appears to increase the conductance to both sodium and potassium whereas at others its effect is primarily on the sodium conductance. These results obtained by studying the reversal potential for the extracellularly recorded glutamate potential under conditions of varied extracellular sodium and potassium concentrations.

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