Membrane electrical properties of frog slow muscle fibres.

Gilly, W F; Hui, Chiu Shuen

doi:10.1113/jphysiol.1980.sp013196

Cited by 22 publications

(8 citation statements)

References 27 publications

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“…INTRODUCTION Adrian, Chandler & Hodgkin (1970a,b) described the kinetic behaviour of the delayed rectifier K channels in voltage-clamped frog skeletal muscle employing an n4 Hodgkin-Huxley model, however, they inferred the existence of a more slowly activating current. Slow currents were also observed by Stanfield (1970a, b), Gilly & Hui (1980b), Almers & Palade (1981), and by Sanchez & Stefani(1978). Throughout, the slow currents were found to be relatively resistant to the K-channel blocker, tetraethylammonium (TEA).…”

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confidence: 74%

“…No fibres studied exhibited the very high membrane resistance described in frog muscle fibres (Gilly & Hui, 1980b) In order to detect the possible presence of slow fibres, contractures were induced in isolated lumbricalis muscles by depolarization with 80 mM-K+ isotonic Ringer solution. Tension declined to less than 15 0 of peak contracture tension after 1 min and to less than 3 % of control after 3 min.…”

Section: Resting Fibre Characteristicsmentioning

confidence: 99%

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Ionic conductances in frog short skeletal muscle fibres with slow delayed rectifier currents.

Lynch¹

1985

The Journal of Physiology

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SUMMARY1. Short (0-81-6 mm) lumbricalis fibres of Rana pipiens were voltage clamped by a two-micro-electrode technique at 5 TC in sucrose hypertonic Ringer solution (SHR). Terminated linear cable analysis suggests that if the current electrode is placed near the centre of the fibre length and the voltage-sensing electrode is placed 0-19 times the fibre length from the current electrode, the fibre can be adequately voltage clamped and the conductance may be simply calculated as I/V for fibre length constants from 1-0 to 0-15 mm.2. In SHR solution lumbricalis fibres have action potentials with peak amplitudes of only + 2 to 7 mV and a slow, gradual repolarization, distinct from the action potentials observed in sartorius muscle. In 60 mM-Na+ SHR the inward Na current could be adequately controlled over the fibre length, providing an estimated Na conductance (GNa) of 8-9 mS/cm2. The magnitude of GNa and GK (delayed rectifier) in lumbricalis fibres was approximately 20 % of that reported for sartorius and semitendinosus, although the resting conductances were similar.3. Fibres demonstrated delayed rectifier currents with complex patterns of activation suggesting two components of conductance (fast, GKrf and slow, GKS) which were combined together in varied amounts: (a) GK,f activated rapidly to a maximum within 80 ms at 0 mV as previously described (Adrian, Chandler & Hodgkin, 1970a); (b) GKS activated gradually with depolarizations below -50 mV and achieving peak currents at about 400 ms at 0 mV.4. In about 10 % of lumbricalis fibres studied, GKS occurred in isolation with a peak magnitude of 1-4+004 mS/cm2 (± S.D.). GKS activation kinetics and tail currents are described by a squared two-state (12) Hodgkin-Huxley model and have a Q10 of 2-8. These currents inactivated with a time constant of 5-7 s at 0 mV. Isolated ,Ks with identical kinetics was also observed in certain sartorius fibres studied with the three-electrode voltage clamp.5. The fractional amount of GKs in the combined delayed rectifier (GKS + GKf) currents could be estimated from analysis of the late activation phase with depolarization. Combined delayed currents were described by summing GKJf currents using a n4 model with GK s currents defined by the 12 model.

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confidence: 74%

Section: Resting Fibre Characteristicsmentioning

confidence: 99%

Ionic conductances in frog short skeletal muscle fibres with slow delayed rectifier currents.

Lynch¹

1985

The Journal of Physiology

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“…Nonlinear charge movement was measured by using the procedures and methods of analysis of Chandler et al (12) and of Gilly and Hui (13,14). In order to record this nonlinear capacitive current, which is small in magnitude, other currents flowing in parallel pathways must be minimized.…”

Section: Methodsmentioning

confidence: 99%

Charge movement in skeletal muscle fibers paralyzed by the calcium-entry blocker D600.

Hui¹,

Milton²,

Eisenberg³

1984

Proc. Natl. Acad. Sci. U.S.A.

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We report measurements of nonlinear charge movement in frog skeletal muscle fibers paralyzed by the calcium-entry blocker [Schwartz, A. & Taira, N., eds. (1983) Circ. Res. 52, Part II, Number 2, 1-181.1 D600 (methoxyverapamil, recently renamed gallopamil). Nonlinear charge movement was not seen in such fibers, suggesting that the drug severs the link between membrane depolarization and the main components of charge movement. This is the only pharmacological agent that blocks the main components of charge movement.While current carried by ions across membranes has been studied for many years, nonlinear capacitive currents within membranes have been recorded only in the last decade. Armstrong and Bezanilla (1) measured a nonlinear capacitive current in the membrane of squid axon. Since then, substantial evidence (?) has been gathered supporting the hypothesis that this current arises from the movement of a "voltage sensor," which controls the conformation and, thus, the conductance of the sodium channel. This Here we report a study of the relationship of charge movement and contraction in skeletal muscle. We find that charge movement is absent in paralyzed fibers but present in revived fibers. This result supports the hypothesis that charge movement is responsible for T tubule-to-SR coupling. MATERIALS AND METHODSEarly experiments were performed on whole sartorius muscles of Rana temporaria. In later experiments, semitendinosus muscles were thinned to several layers of fibers, exposing the fiber ends at the tendon and reducing connective tissue interference with solution changes and microelectrode impalement. The paralyzing treatment of muscle fibers has been described and documented in detail (11). Briefly, a muscle was presoaked in normal Ringer containing 30 /iM D600 at about 59C. A high (190 mM) potassium solution at 50C also containing 30 ,uM D600 was applied for 30 sec to depolarize the fibers. The muscle was then soaked in normal Ringer's solution for 10-30 min, and the contractility of surface fibers was checked. If randomly selected surface fibers did not move in response to depolarizing current from an inserted microelectrode, as observed under a compound microscope, the experiment commenced. If the fiber moved in response to depolarization, then a second and sometimes a third contracture was elicited. Surface fibers of these whole muscles were always paralyzed after three applications of potassium, usually after two, and often after one.Nonlinear charge movement was measured by using the procedures and methods of analysis of Chandler et al. (12) and of Gilly and Hui (13,14). In order to record this nonlinear capacitive current, which is small in magnitude, other currents flowing in parallel pathways must be minimized. Nonlinear ionic currents were reduced by channel blockers, and linear current was removed by subtraction. The following bathing solution minimizes nonlinear ionic currents: 115 mM tetraethylammonium chloride containing 5 mM RbCl, tetrodotoxin (10 ttg/ml), 30 puM D600, 11.8 mM C...

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“…4 can be explained by a simultaneous activation of K+ outward currents which, as already shown, are not completely blocked by TEA (see Figs. 2 and 3) and can be activated during large depolarizations (Stefani & Uchitel, 1976;Gilly & Hui, 1980b).…”

Section: Tonic Fibre Identificationmentioning

confidence: 99%

Calcium action potentials and calcium currents in tonic muscle fibres of the frog (Rana pipiens).

Huerta¹,

Stefani²

1986

The Journal of Physiology

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SUMMARY1. Slow action potentials were evoked in cruralis tonic and twitch fibres of the frog after drastically reducing the Cl-and K+ conductances.2. Tonic fibres were identified by their electrical characteristics. They had an effective resistance (Reff) of 50 + 6 Mf (n = 27) and a membrane time constant (Tm) of 440+70 ms (n = 8). In twitch fibres Reff = 2-9+003 Mil (n = 16) and Tm = 50+4 ms (n = 6). 3. In tonic fibres the slow action potential had a threshold of -50 to -60 mV and a peak amplitude of -10 mV. In twitch fibres the slow action potential had a threshold of -40 mV and reached a peak amplitude of + 40 mV.4. The responses were blocked by the addition ofCd2+ (2 mM) or Co2+ (5 mM). These results strongly suggest that Ca2+ is the main carrier of current during the response.5. Using the three-micro-electrode voltage-clamp technique a slow inward membrane current underlying the Ca2+ potential could be described in tonic muscle fibres.6. The slow inward current was mainly carried by Ca2+, since it was reduced when external Ca2+ concentration was lowered or when Cd2+ (2 mM) was added. Moreover, Ca2+ was the only cation in the solution that could carry inward current. It had a mean threshold of -60 mV, reached a maximum value at ca. 0 mV, ranged from 24 to 28 ,sA/cm2 and had a mean reversal potential of + 35 mV.7. In about half of the examined tonic fibres inward current declined with time, only slowly. This can either be explained by there being less contamination by K+ outward current, or by the presence of two types of Ca2+ channels in the tonic fibre membrane.

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Membrane electrical properties of frog slow muscle fibres.

Cited by 22 publications

References 27 publications

Ionic conductances in frog short skeletal muscle fibres with slow delayed rectifier currents.

Ionic conductances in frog short skeletal muscle fibres with slow delayed rectifier currents.

Charge movement in skeletal muscle fibers paralyzed by the calcium-entry blocker D600.

Calcium action potentials and calcium currents in tonic muscle fibres of the frog (Rana pipiens).

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