Membrane electrical properties of developing fast‐twitch and slow‐tonic muscle fibres of the chick.

Poznansky, Mark J.; Steele, Joy A.

doi:10.1113/jphysiol.1984.sp015087

Cited by 9 publications

(4 citation statements)

References 33 publications

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“…Poznansky & Steele (1984) have demonstrated that at 1 week prior to hatching, there is little detectable resting chloride conductance in chick fast-twitch muscle. However, by the time of hatching, 70 % of the resting membrane conductance is due to chloride, as is also found in the adult (Lebeda & Albuquerque, 1975).…”

Section: Discussionmentioning

confidence: 99%

A calcium‐ and voltage‐dependent chloride current in developing chick skeletal muscle.

Hume

Thomas

1989

The Journal of Physiology

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SUMMARY1. Depolarization of embryonic chick myotubes from negative potentials elicits a rapid spike followed by a long-duration after-potential. The ionic basis of the longduration after-potential was examined by making intracellular recordings from cultured myotubes, and by making whole-cell patch-clamp recordings from myoblasts and myoballs.2. The peak potential of the long-duration after-potential varied with the chloride gradient, suggesting that a conductance increase to chloride is involved in generating the after-potential. However, a calcium current was also implicated, since lowering the extracellular calcium or replacing extracellular calcium with cobalt abolished the after-potential.3. When extracellular calcium was replaced with strontium or barium, shortduration spikes similar to calcium spikes were observed, but only strontium was able to support activation of long-duration after-potentials. Intracellular injection of calcium or strontium into myotubes bathed in calcium-free extracellular solutions restored the ability of depolarization to evoke an after-potential. Intracellular injection of magnesium, barium, nickel or cobalt did not restore this ability. These experiments strongly suggested that the long-duration after-potential was due to a calcium-and voltage-activated chloride current.4. Whole-cell voltage-clamp recordings from myoballs and myoblasts showed that a large chloride conductance could be activated by depolarization when the internal free calcium concentration was buffered at levels greater than 10-7 M. At 2-5 x 10-7 Mcalcium, the voltage dependence of activation was steepest in the range of -30 to -20 mV and the activation kinetics varied with the membrane potential. The time to half-maximal activation ranged from 01 s at positive potentials to greater than 1 s at more negative potentials. The time constant for deactivation was approximately 1 s at -50 mV. No inactivation was observed.5. The selectivity of the chloride current was measured by substituting other anions for chloride. The following permeability series was found: I-> NO3-> Br-> C1-> acetate > F-> S04-= glucuronate. Thus anion permeability decreased as the hydration radius increased.6. Measurements of the resting potential of developing myoblasts and myotubes under 'physiological' conditions (37°C, bicarbonate buffer) suggest that the afterpotential acts to depolarize these cells 10-20 mV above their resting potential (approximately -60 mV) for several seconds. R. 1. HlUMAlE AND S. A. THOMAS 7. We discuss the possibility that the long-duration after-potential may be involved in triggering myoblast fusion and in the generation of bursts of spontaneous contractions in developing myotubes.

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Section: Discussionmentioning

confidence: 99%

A calcium‐ and voltage‐dependent chloride current in developing chick skeletal muscle.

Hume

Thomas

1989

The Journal of Physiology

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“…In order to apply a voltage clamp technique to the embryonic fibers, it was necessary to isolate single fibers by an enzymatic and mechanical dissociation procedure (Poznansky and Steele, 1984). Briefly, muscles were incubated in Eagle's minimum essential medium (MEM; Gibco, Calgary, Alberta) containing 0.3% collagenase (Type I, Sigma, St. Louis) for 3 h at 37°C in a humidified, 5% CO, atmosphere.…”

Section: Methodsmentioning

confidence: 99%

“…As well, chloride channels that are open at the resting membrane potential could also be involved in repolarization. The resting chloride conductance has been shown to in- (cl)l/(cl)o crease dramatically during the developmental stages studied here (Poznansky and Steele, 1984). The action potential has an unusually long refractory period.…”

Section: Experiments On Isolated Myoballsmentioning

confidence: 97%

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Chloride action potentials and currents in embryonic skeletal muscle of the chick

Steele

1990

Journal Cellular Physiology

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Chloride-dependent action potentials were elicited from embryonic skeletal muscle fibers of the chick during the last week of in ovo development. The duration of the action potentials was extremely long (greater than 8 sec). The action potentials were reversibly blocked by the stilbene derivative, SITS, a specific blocker of chloride permeability. Using patch clamp pipettes, in which the intracellular chloride concentration was controlled and with other types of ion channels blocked, the membrane potential at the peak of the action potential closely coincided with the chloride equilibrium potential calculated from the Nernst equation. These data indicate that activation of a chloride-selective conductance underlies the long duration action potential. The occurrence of the chloride-dependent action potential was found to increase during embryonic development. The percentage of fibers that displayed the action potential increased from approximately 20% at embryonic day 13 to approximately 70% at hatching. Chloride-dependent action potentials were not found in adult fibers. The voltage and time-dependent currents underlying the action potential were recorded under voltage clamp using the whole-cell version of the patch pipette technique. The reversal potential of the currents was found to shift with the chloride concentration gradient in a manner predicted by the Nernst equation, and the currents were blocked by SITS. These data indicate that chloride ions were the charge carriers. The conductance was activated by depolarization and exhibited very slow activation and deactivation kinetics.

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Muscle

Harvey¹,

Marshall²

1986

Avian Physiology

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Membrane electrical properties of developing fast‐twitch and slow‐tonic muscle fibres of the chick.

Cited by 9 publications

References 33 publications

A calcium‐ and voltage‐dependent chloride current in developing chick skeletal muscle.

A calcium‐ and voltage‐dependent chloride current in developing chick skeletal muscle.

Chloride action potentials and currents in embryonic skeletal muscle of the chick

Muscle

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