Voltage—clamp analysis of the early current in frog skeletal muscle fibre using the double sucrose‐gap method

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SUMMARY1. The outward currents underlying delayed rectification have been studied in frog auricular trabeculae with the double sucrose gap method.2. The results obtained in our experimental conditions allow us to discard the hypothesis of an accumulation of ions during the flow of the outward current.3. In most of the cases the delayed current is composed of two components similar to those previously described by Noble & Tsien (1969 a, b).4. The first component I is activated with a time constant of about 0-3 see at the resting potential (E = -70 mV) and of about 0 75 see at E = -5 mV. The steady-state value of the degree of activation (xj)O, varies from 0 at E = -90 mV to 1 at E = + 20 mV. The reversal potential is near E = -80 mV; this current seems to be mainly carried by potassium ions.5. The second component I2 is very slowly activated, with a time constant of 3-5 see at E = -70 mV and of 5 sec at E =-5 mV. The steadystate value of the degree of activation (x2)0, varies from 0 at E = -40 mV to 1 at E = + 25 mV. The reversal potential is near E =-60 mV; this current is less specific than the first component.6. In some preparations the delayed current is composed of only one component. This current is activated with a time constant of 0*6 see at the resting potential and of 1-5 sec at E =-5 mV. The steady-state value of the degree of activation is 0 at E =-90 mV and 1 at E = + 30 mV. The reversal potential is between E = -70 and E = -60 mV. * Present and reprints address: Dr 0. Rougier, Laboratoire de Physiologie de3

“…The double sucrose-gap perfusion bath and the electronic apparatus were the same as previously described (Rougier et al 1968;Ildefonse & Rougier, 1972).…”

Section: Methodsmentioning

confidence: 99%

Kinetic analysis of the delayed outward currents in frog atrium. Existence of two types of preparation

Ojeda¹,

Rougier²

1974

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“…2A shows the decay of the current induced by a 20 mV depolarization (a) in normal Ringer solution containing TTX, (b) when Cl-and Ca2+ are absent and (c) when 0 5 mM-EGTA is then added. Some passive electrical properties ofthe membrane have been calculated for an equivalent circuit derived by Ildefonse & Rougier (1972) from that given by Falk & Fatt (1964). The results obtained for seven fibres are listed in Table 2.…”

Section: Determination Of the Composition Of The Experimental Solutionsmentioning

confidence: 99%

Existence of a sodium‐induced calcium release mechanism of frog skeletal muscle fibres.

Potreau¹,

Raymond²

1982

SUMMARY1. The electrical and the mechanical activity of isolated frog muscle fibres have been simultaneously recorded in a physiological solution which allows the development of a large tubular sodium current.2. Under such experimental conditions, fibres develop long-lasting action potentials and strong mechanical responses.3. In voltage-clamp experiments a slow inward current is revealed for depolarizations higher than + 20 mV from the resting potential. This current increases until + 40 to + 50 mV and then decreases to reverse near + 90 mV. The amplitude of the mechanical response increases with the potential to reach an optimum value between + 40 and + 50 mV and then decreases to stabilize when the depolarization is near + 90 mV.4. In the presence of picrotoxin the slow inward current is reversibly inhibited and the tension-depolarization curve has an S-shape as found in normal physiological conditions. 5. The dependence of a part of the contraction upon the slow inward current is reinforced by the fact that in a 50 % sodium solution the amplitude of the current and that of the contraction are reduced in the same proportion. 6. Detubulated fibres failed to generate such a sodium inward current. 7. When sodium ions are replaced by lithium ions a slow inward lithium current develops but it does not induce a mechanical response.8. Tetracaine reversibly inhibits the current-dependent component of the contraction without affecting the potential-dependent one.9. It is concluded that the contraction recorded in the present experimental conditions is the sum of two components: one is potential-dependent and the other depends on a sodium-induced calcium release mechanism.

“…In sodium-free solution (choline chloride or sucrose replacement) as well as in chloride-free solution (L-glutamate replacement), the amplitude of the delayed outward current was only slightly reduced and its time course was unaffected. The effect of zero sodium solution has already been described in frog muscle by Ildefonse & Rougier (1972). The decrease in the amplitude of the delayed outward current in chloride-free solution could either be real or due to an effect of chloride ions on the background current.…”

Section: Nature Of the Outward Currentsmentioning

confidence: 98%

Ionic currents in slow twitch skeletal muscle in the rat.

Duval¹,

Léoty²

1980

SUMMARY1. The ionic currents in slow fibres isolated from rat soleus muscle have been studied under voltage-clamp conditions with a double sucrose-gap method and the results are compared to those obtained from fast fibres isolated from the iliacus muscle.2. The mean value of the resting potential in slow fibres is -70 mV, a value 8 mV more positive that the mean resting potential of fast fibres (-78 mV).3. In slow muscle, a fast inward current which is blocked by tetrodotoxin and which depends on external sodium concentration is presumed to be carried by sodium ions. The characteristics of this current, which are time-and voltagedependent, are similar to those of the iliacus fibres. From a holding potential at -86 mV, this inward current is maximal (2-6 mA/cm2 + 0.3) at + 491 mV + 1.5 (mean + S.E. of mean), reverses at + 127-3 mV + 2-2 (mean+ S.E. of mean), and its half inactivation occurs at + 23-2 mV + 0-8 (mean + s.E. of mean).4. The delayed outward current in slow fibres is unchanged by exposure to chloride free solution and has a time course very different from that found in fast fibres. This current reaches an initial peak in 5-10 msec and a second peak or steady level after 40-150 msec. The decay of the outward current is also very different, being ten times slower than that in fast fibres (1500-3000 msec).5. Analysis of the tail currents reveals the existence of two components of delayed current in slow fibres. The faster component reverses at a potential of 113 mV + 0 9 (mean + s.E. of mean) positive to the holding potential (equivalent to a membrane potential of about -75 mV), in contrast to a reversal potential of 35.4 mV + 2-5 (mean + S.E. of mean) positive to the holding potential for the slower component (equivalent to a membrane potential of about -51 mV.6. In L-glutamate solution the characteristics of the inward-going rectification are the same in the two types of muscle.