Perchlorate and the relationship between charge movement and contractile activation in frog skeletal muscle fibres.

The intramembrane charge movement in skeletal muscle includes at least two major current contributions. Under normal conditions, the imposition of progressively larger voltage-clamp steps in intact fibres first elicits early, 1. The effects of perchlorate ions on intramembrane charge movements were examined under different conditions of ryanodine receptor (RyR) modification in intact voltage-clamped amphibian skeletal muscle fibres studied in the gluconate-containing solutions previously reported to emphasize the features of qã at the expense of those of the qâ charge. 2. The introduction of graded increases in perchlorate concentration to the experimental solutions selectively shifted the threshold of appearance of the qã 'hump' currents to more negative test potentials at which they actually appeared in the absence of prior qâ transients at perchlorate concentrations of 4·0-8·0 mÒ. Such findings suggested that the delayed (qã) transitions can take place independently of any previous exponential (qâ) decay. 3. These kinetic effects were accompanied by hyperpolarizing shifts in the transition potentials (V*) of the steady-state voltage dependences of either the overall or the isolated qã charge. These shifts were graded with concentration and reached their maximum effects at 4·0-8·0 mÒ perchlorate. However, both the total charge (Qmax) and the steepness factor (k) remained conserved at values consistent with a system that included significant contributions from the steeply voltage-sensitive qã component (overall charge: Qmax 19-21 nC ìF¢, k 7-9 mV; qã component alone: Qmax 10-12 nC ìF¢, k 4-6 mV). This contrasts with earlier reports on the effects of perchlorate in fibres that were studied in sulphate-or methanesulphonate-containing extracellular solutions. 4. Perchlorate (8·0 mÒ) restored the 'hump' waveform associated with qã charge movements that had previously been obliterated by the prior application of fully effective (0·1 mÒ) concentrations of either ryanodine or daunorubicin. 5. Perchlorate similarly reversed the positive shift in the transition potential of the qã component that was brought about by such RyR modification (from V* −40 mV back to V* −60 mV). In contrast, the values of either Qmax (overall charge, 19-21 nC ìF¢; qã component, 10-13 nC ìF¢) or k (overall charge, 7-9 mV; qã component, 4-6 mV) remained conserved through all these experimental manoeuvres. 6. The inclusion of perchlorate also reversed the action of 2 mÒ tetracaine and restored delayed qã transients to an extent that was graded with concentration (0·5-8·0 mÒ perchlorate).There was an accompanying recovery of the steeply voltage-dependent steady-state (qã) component consistent with a competitive interaction between these agents upon the qã intramembrane charge. 7. The present findings suggest that perchlorate exerts a specific action upon the qã charge in independent transitions that are driven by the tubular membrane field. Its interactions with the known RyR inhibitors that nevertheless conserve both the charge and its voltage...

Section: Discussioncontrasting

confidence: 88%

The influence of perchlorate ions on complex charging transients in amphibian striated muscle

Huang

1998

“…7 of Csernoch et al 1987). It is expected therefore that the threshold voltage for Ca2+ release will be reached earlier in the action potential in presence of SCN-, and that the Ca signal will depart from baseline at an earlier time relative to the onset of the action potential.…”

Section: Lyotropic Anions and Ca Signalsmentioning

confidence: 99%

“…A number of these effects are in common with those of the lyotropic or chaotropic anion perchlorate (C104), which likewise shifts the voltage dependence of force activation and charge movement to more negative potentials, prolongs the time 464 ACTIONS OF LYOTROPIC ANIONS ON FROG MUSCLES course of the 'off' charge movement, and is effective both intracellularly and extracellularly (Gomolla, Gottschalk & Liittgau, 1983;Huang, 1986Huang, , 1987Csernoch et al 1987). The similarity is only partial, however.…”

Section: Lyotropic Anions Charge Movement and Icamentioning

confidence: 99%

“…This is consistent with models in which charge movement couples to Ca2+ release, especially given the observed effects of SCN-on the voltage dependence of charge 1. SCN-may therefore share with C104-the 466 ACTIONS OF LYOTROPIC ANIONS ON FROG MUSCLES property of modifying the calcium release process by acting on the charge movement step of the release process (Gomolla et al 1983;Csernoch et al 1987).…”

Section: Lyotropic Anions and Ca Signalsmentioning

confidence: 99%

See 1 more Smart Citation

The effects of lyotropic anions on charge movement, calcium currents and calcium signals in frog skeletal muscle fibres.

DeLay¹,

García²,

Sánchez³

1990

SUMMARY1. Intramembrane charge movement and Ca2+ currents were monitored in voltage-clamped segments of frog skeletal muscle fibres using the triple-Vaseline-gap technique. Calcium signals were measured in current-clamped fibres using either of the indicators Arsenazo III or Antipyrylazo III.2. Non-linear capacitative currents (charge 1) were obtained using a subtraction procedure which employed either a -20 mV control pulse from a holding potential of -100 mV or alternatively a control pulse to + 80 mV in depolarized fibres. The amount of charge mobilized depended on voltage according to a two-state Boltzmann function. The total charge (Qmax) was increased by ca 100% and the steepness parameter (k) by ca 70 % when a + 80 mV control pulse was used.3. Thiocyanate (SCN-) and other lyotropic anions reversibly shifted the voltage dependence of mobilized charge towards negative potentials. Qmax was not significantly affected. 'Off' charge tails were greatly prolonged by lyotropic anions.4. Extracellularly applied lyotropic anions affected the dihydropyridine-sensitive Ca2+ current by shifting the I-V relation toward more negative voltages and delaying deactivation of the tail currents.5. The effects of lyotropic anions did not depend on whether the anion was introduced intracellularly or extracellularly.6. Extracellular SCN-reversibly increased the peak amplitude and rate of rise of Ca signals, and decreased the latent period between stimulation and onset of the Ca signal.7. It is concluded that lyotropic anions have similar effects on Ca2+ currents and on charge movement.

“…Such a negative phase was absent in all our published charge movement records having prominent 17 humps (Hui, 1983a(Hui, , b, 1990(Hui, , 1991aHui & Milton, 1987;Chen & Hui, 1991a, b;Hui & Maylie, 1991;Hui & Chen, 1992a, b) and in numerous records obtained by other investigators (Adrian & Peres, 1977, 1979Horowicz & Schneider, 1981a, b;Huang, 1981Huang, , 1982Huang, , 1983Huang, , 1987Vergara & Caputo, 1983;Adrian & Huang, 1984;Rakowski, Best & James-Kracke, 1985;Csernoch, Kovacs & Szucs, 1987;Csernoch, Huang, Szucs & Kovacs, 1988;Feldmeyer, Csernoch, Kovacs & Thieleezek, 1988;Caputo & Bolanios, 1989;Etter, 1990;Delay, Garcia & Sanchez, 1990 become clear below, we define it as the 'dip in current' throughout this paper. It should be emphasized that even if the dip in current appears to drop below the axis of abscissae, it does not necessarily represent an inward current because the true baseline could be below the axis of abscissae.…”

mentioning

confidence: 60%

Evidence for the non‐existence of a negative phase in the hump charge movement component (I gamma) in Rana temporaria.

Hui

Chen

1994

could only be observed in a very narrow potential range and might not persist until the end of the experiment. 4. A replacement of the Cl-in the external solution by CH3SO3-reduced the magnitude of the dip, suggesting that the dip is ionic in origin. 5. When charge movement was measured in slack fibres (2 2 ,um sarcomere length), the probability of observing the dip in current was increased. 6. In some experiments in which the dip in current was very stable, the signal was studied by a sequence of TEST pulses to the same potential but with different durations. It was found that, if the dip in current was included as a negative phase of the Iy hump, then the amount of ON charge was smaller than that of OFF charge. Also, as the pulse duration was increased progressively so that a longer portion of the dip was recorded, the OFF charge remained constant instead of being decreased. 7. These results suggest that the dip in current cannot be a negative phase of the Ir hump, but probably arises from the superposition of the decaying phase of the Iy hump and a slowly rising ionic current.When measured under appropriate conditions, the ON charge movement transient in frog skeletal muscle fibres shows two components, the early I, component and the delayed 17 hump. In the 'feedback hypothesis', I presumably triggers Ca2+ release from the sarcoplasmic reticulum. The released Ca2+ diffuses rapidly across the narrow gap separating the sarcoplasmic reticulum and the transverse tubule, binds to the myoplasmic face of the tubular membrane and causes a secondary depolarization of the membrane. Consequently, more charges are mobilized, generating the delayed I1 hump. A corollary to the hypothesis is that, if the depolarization is held sufficiently long for the bound Ca2" to come off the tubular membrane, an inward charge movement could occur after the 17 hump.Such a negative phase was absent in all our published charge movement records having prominent 17