Origin of delayed outward ionic current in charge movement traces from frog skeletal muscle.

Hui, Chiu Shuen; Chen, Wei

doi:10.1113/jphysiol.1994.sp020281

Cited by 9 publications

(17 citation statements)

References 33 publications

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“…The most ideal end‐pool solution to study charge movement in cut fibres is one containing 20 m m EGTA without added Ca 2+ , although it is non‐physiological. This solution blocks fibre contraction conveniently, stabilizes the fibre for several hours, and suppresses the Ca 2+ ‐dependent Cl − current (Hui & Chen, 1994). An additional advantage revealed in this paper is that it provides a condition for more convenient studies of Q γ .…”

Section: Discussionmentioning

confidence: 99%

“…Experiments were performed on cut fibres containing 0.1 m m EGTA under otherwise identical conditions to those in which we observed prominent I γ humps. Because of the existence of a Ca 2+ ‐dependent Cl − current in the absence of high [EGTA] i (Hui & Chen, 1994), the Cl − in the external solution had to be replaced with an impermeant anion. Additionally, the fibre segments had to be highly stretched to suppress contraction.…”

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Charge Movement in Cut Twitch Fibres of Rana Temporaries Containing 0.1 mm EGTA

Hui

Chen

1997

The Journal of Physiology

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Charge movement was studied in the cut twitch fibres of Rana temporaria with a double Vaseline‐gap voltage‐clamp technique. In fibres containing 0.1 mm EGTA, the Iγ hump component of charge movement was either unresolvable or had a brief duration at all potentials. In the steady‐state charge‐voltage (Q–V) plots that were separable into the less voltage dependent (Qβ) and more voltage dependent (Qγ) components, the amount of Qγ was 0.9 ± 0.1 nC μF−1 (mean ±s.e.m., n= 18). Fibres containing 20 mm EGTA showed broad Iγ humps at about −45 mV. The addition of 1.8 mm total Ca2+ to the end‐pools accelerated the rising phase and abbreviated the duration of the hump. I γ humps in fibres containing 0.1 mm EGTA resembled those in intact fibres when recorded at similar low temperatures. These results explain the controversy concerning the variable appearance of Iγ humps in cut fibres.

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Section: Discussionmentioning

confidence: 99%

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confidence: 99%

Charge Movement in Cut Twitch Fibres of Rana Temporaries Containing 0.1 mm EGTA

Hui

Chen

1997

The Journal of Physiology

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“…In measuring charge movement in cut fibres, we routinely used 20 mM EGTA in the end‐pool solution to suppress fibre contraction (beginning with Hui & Chandler, 1990). The presence of EGTA has the additional advantages of stabilizing the fibre for several hours, suppressing the calcium‐dependent Cl − current (Hui & Chen, 1994) and enhancing the appearance of the I γ hump (Hui & Chen, 1997). However, this high [EGTA] i reduces the resting free [Ca 2+ ] in the myoplasm to far below the physiological level, thereby reducing the Ca 2+ reloading of the sarcoplasmic reticulum (SR) after activities.…”

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confidence: 99%

A slow calcium‐dependent component of charge movement in Rana temporaria cut twitch fibres

Hui

1998

The Journal of Physiology

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Charge movement was studied in highly stretched frog cut twitch fibres in a double Vaseline‐gap voltage‐clamp chamber, with the internal solution containing either 0.1 mM EGTA or 20 mM EGTA plus 1.8 mM total Ca2+. Fibres were stimulated with TEST pulses lasting 100‐400 ms. Replacement of the external Cl− with an ‘impermeant’ anion, such as SO42‐, CH3SO3−, gluconate or glutamate, greatly reduced the calcium‐dependent Cl− current in the ON segment and generated a slowly decaying inward OFF current in charge movement traces. Application of 20 mM EGTA to the internal solution abolished the slow inward OFF current, implying that the activation of the current depended on the presence of Ca2+ in the myoplasm. The possibility that the slow inward OFF current was carried by cations flowing inwards or anions flowing outwards was studied and determined to be unlikely. During a long (2000 ms) TEST pulse, a slowly decaying ON current was also observed. When the slow ON and OFF currents were included as parts of the total charge movement, ON‐OFF charge equality was preserved. This slow capacitive current is named Iδ. When Cl− was the major anion in the external solution, the OFF Iδ was mostly cancelled by a slow outward current carried by the inflow of Cl−. The OFF Iδ component showed a rising phase. The average values of the rising time constants in CH3SO3− and SO42‐ were similar and about half of that in gluconate. The OFF Iδ component in CH3SO3− had a larger magnitude and longer time course than that in SO42‐. The maximum amount of Qδ in CH3SO3− was about three times as much as that in SO42‐, whereas the voltage dependence of Qδ was similar in the two solutions. Since the existence of Qδ depends on the presence of Ca2+ in the myoplasm, it is speculated that Qδ could be a function of intracellular calcium release.

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“…Furosemide, a compound related to bumetanide, also inhibits the NKCC albeit at order-of magnitude-higher concentrations. However, furosemide is not specific to the NKCC and is a more general inhibitor of Cl -flux in cells, known to inhibit KCl cotransport [12] and calcium-dependent Cl -channels [13]. Using rat skeletal muscles in vitro at room temperature, Sitdikov and coworkers [14] noted that exposure to hypertonic solution resulted in a decrease in cell volume that was followed by a slow increase in volume back to normal levels.…”

Section: Introductionmentioning

confidence: 99%

K<sup>+</sup> Transport and Volume Regulatory Response by NKCC in Resting Rat Hindlimb Skeletal Muscle

Lindinger

Hawke

Lipskie

et al. 2002

Cell Physiol Biochem

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This study tested the hypothesis that the NKCC is involved in volume regulation, specifically regulatory volume increase (RVI), in resting skeletal muscle. Neurally and vascularly isolated rat hindlimbs were perfused with a bovine erythrocyte perfusate containing ⁴²K or ⁸⁶Rb as markers of unidirectional K⁺ flux across the sarcolemma. Compared to controls, perfusion with 120 µM bumetanide (a specific inhibitor of the NKCC) decreased J_inK by 15±2%, indicating the functional presence of the NKCC. Experiments with ouabain (to block active K⁺ transport by the Na,K ATPase) showed that the bumetanide-sensitive component of J_inK comprised 35% of the total ouabain-sensitive J_inK. Inhibition of NKCC resulted in a net loss of water by muscle. When hindlimbs were perfused with hypertonic (380 mOsm/L by addition of sucrose) perfusate for 20 min, after initially blocking K⁺ channels with 1 mM barium, J_inK rapidly (2-3 min) increased 2-fold followed by a rapid decline. This rapid, transient increase in J_inK was abolished with bumetanide, confirming that perfusion with hypertonic perfusate stimulated NKCC activity and RVI. The hypertonic perfusate also resulted in temporally associated decreases in net water uptake by muscle. It is concluded that a functional NKCC is present in mammalian skeletal muscle and that it is involved in cell volume regulation.

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Origin of delayed outward ionic current in charge movement traces from frog skeletal muscle.

Cited by 9 publications

References 33 publications

Charge Movement in Cut Twitch Fibres of Rana Temporaries Containing 0.1 mm EGTA

Charge Movement in Cut Twitch Fibres of Rana Temporaries Containing 0.1 mm EGTA

A slow calcium‐dependent component of charge movement in Rana temporaria cut twitch fibres

K<sup>+</sup> Transport and Volume Regulatory Response by NKCC in Resting Rat Hindlimb Skeletal Muscle

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