Inactivation of Calcium Currents in Insect Skeletal Muscle

Ashcroft, Frances M.; Stanfield, Peter

doi:10.1016/b978-0-12-524980-5.50015-6

Cited by 3 publications

(2 citation statements)

References 14 publications

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“…Both of these outward currents are carried by potassium ions. A preliminary account of some of these results has appeared already (Ashcroft, Standen & Stanfield, 1979).…”

Section: Introductionmentioning

confidence: 94%

Calcium and potassium currents in muscle fibres of an insect (Carausius morosus).

Ashcroft¹,

Stanfield²

1982

The Journal of Physiology

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SUMMARY1. A three electrode voltage-clamp was used to investigate membrane currents in the skeletal muscle fibres of the stick insect, Carausius morosus. Contraction was blocked by hypertonic solutions.2. Membrane currents elicited by step depolarizations consisted of an inward current, an early outward current and a delayed outward current.3. The reversal potential of the delayed outward current did not change when S042-was substituted for Cl-, but shifted by 14-1 mV when [K]o was increased from 20 mM to 40 mm in S042-solution, suggesting that the delayed current is carried by K+. Both early and delayed outward currents were substantially reduced by 120 mMtetraethylammonium (TEA) ions. 4. The small size of the shift in the reversal potential ofthe delayed outward current with increased pulse duration suggests that the delayed current measured flows mainly across the surface membrane.5. Increasing [Ca]o made the apparent reversal potential for the inward current (120 mM-TEA Ringer) more positive and increased the size of the maximum inward current. However, Ca-currents showed saturation with increasing [Ca]0, indicating that there is a site to which Ca ions bind during their passage through the membrane. The dissociation constant of this site was 7-3 mm at 0 mV and was voltage-dependent.

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“…Both of these outward currents are carried by potassium ions. A preliminary account of some of these results has appeared already (Ashcroft, Standen & Stanfield, 1979).…”

Section: Introductionmentioning

confidence: 94%

Calcium and potassium currents in muscle fibres of an insect (Carausius morosus).

Ashcroft¹,

Stanfield²

1982

The Journal of Physiology

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“…We initially attempted to fit the steady-state inactivation of the Ca current as if it were simply potential-dependent (Ashcroft, Standen & Stanfield, 1979). We used a two pulse protocol to examine this, with an inactivating pulse of 1 sec duration preceding a test pulse to 0 mV.…”

Section: Voltage-dependence Of Inactivationmentioning

confidence: 99%

Calcium inactivation in skeletal muscle fibres of the stick insect, Carausius morosus.

Ashcroft¹,

Stanfield²

1982

The Journal of Physiology

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SUMMARY1. Inactivation of Ca currents in skeletal muscle fibres of the stick insect, Carausius morosus, was studied using a three-electrode voltage-clamp method.2. The extent of inactivation showed a voltage-dependence similar to that of the Ca current, inactivation being absent in the absence of a Ca current, maximal at potentials where Ca currents are largest, and reduced at potentials close to Eca.3. Ca currents inactivated along a double exponential time course, both when measured from the decline ofCa current during a single pulse and when measured using a two pulse protocol. In 20 mM-Ca-Ringer the fast time constant of inactivation had a mean value of 27 msec and that of the slow time constant was 134 msec, at 0 mV and 5 'C.4. The rate of inactivation was slowed, and its extent reduced, in low [Ca]0, where Ca currents are smaller. Similarly, inactivation was faster and more complete in highCa-Ringer.5. The rate of recovery from inactivation also followed a double exponential time course, with time constants of 638 msec and 4 see following a 500 msec inactivating pulse in 20 mM-Ca-Ringer at 5 'C. Recovery appeared to be related to the amount of Ca entry during the inactivating pulse, being slower in high [Ca]. and following longer inactivating pulses.6. Inactivation was slowed and reduced in extent when Ba2+ or Sr2+ carried current. Inactivation in Ba solutions may be due to depletion of Ba2+ from the lumen of the transverse tubules.7. Ba2+ does not compete with Ca2+ for the inactivation mechanism. 8. It is concluded that inactivation of Ca currents in stick insect muscle fibres is primarily mediated by Ca2+ entry.

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Sodium action potentials induced by calcium chelation in rat uterine smooth muscle

1982

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Inactivation of Calcium Currents in Insect Skeletal Muscle

Cited by 3 publications

References 14 publications

Calcium and potassium currents in muscle fibres of an insect (Carausius morosus).

Calcium and potassium currents in muscle fibres of an insect (Carausius morosus).

Calcium inactivation in skeletal muscle fibres of the stick insect, Carausius morosus.

Sodium action potentials induced by calcium chelation in rat uterine smooth muscle

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