Effects of local anesthetics on single channel behavior of skeletal muscle calcium release channel.

Tetracaine has been a commonly used tool for studying the events of excitation-contraction coupling (E-CC). It not only alters intramembrane charge movement (Huang, 1981;Hui, 1983) but suppresses the calcium transients (Vergara & Caputo, 1983;Csernoch et al. 1988) by interfering with the release of calcium from the sarcoplasmic reticulum (SR; Pizarro et al. 1992). In both intact and cut fibres tetracaine preferentially eliminates the delayed, qã hump, component of intramembrane charge (e.g. , although cut fibres seem to be more sensitive (Csernoch et al. 1988) towards the drug. Most of our knowledge regarding the time course of SR calcium release (for review on calcium release see e.g. Melzer et al. 1995) in the presence of tetracaine was obtained from measurements on frog skeletal muscle fibres. In amphibians the early, inactivating peak of calcium release was suppressed by low (û 20 ìÒ) concentrations of the drug while the maintained steady level was unaffected (Pizarro et al. 1992).

Section: ------------------------------------------------------------supporting

confidence: 75%

mentioning

confidence: 99%

Effects of tetracaine on sarcoplasmic calcium release in mammalian skeletal muscle fibres

Csernoch

Szentesi

Sárközi

et al. 1999

“…The local anaesthetic tetracaine at 200 ìÒ nearly eliminates Ca¥-induced activity of release channels in lipid bilayers (Xu, Jones & Meissner, 1993). This concentration reversibly eliminated sparks (Fig.…”

Section: Resultsmentioning

confidence: 87%

Small event Ca²⁺ release: a probable precursor of Ca²⁺ sparks in frog skeletal muscle

Shirokova

Rı́os

1997

Fluo‐3 fluorescence associated with Ca2+ release was recorded with confocal microscopy in single muscle fibres. Clamp depolarization to −65 or −60 mV elicited Ca2+ sparks with amplitudes and spatial widths distributed approximately normally, with mean values of 0.79 of resting fluorescence and 0.8 μm (S.D., 0.17 and 0.2 μm; n= 193), respectively. Given these distributions, events of amplitude less than 0.45 or width less than 0.4 μm are unlikely to be sparks. Low voltage depolarization (−72 mV) elicited only one spark per triad every 6 s, but generated a relative increase in fluorescence at triads of 0.05. This increase must therefore have been due to events smaller than sparks. The variance/mean ratio of triadic fluorescence gradients averaged 0.11 at low voltages and increased severalfold at the higher voltages at which sparks appeared, indicating the existence of at least two event amplitudes. Tetracaine (200 μm) reversibly abolished sparks and the early peak of Ca2+ release at all voltages. In its presence, discrete events were smaller than the spark criterion, and triadic gradients had a variance/mean ratio of 0.11. The phenylalkylamine D600 (2 μm) reduced release at all voltages, abolishing sparks and the peak of Ca2+ release at low but not at high voltages. The parallel abolition of all sparks and the peak of Ca2+ release indicates that both phenomena are activated by Ca2+. The restoration of sparks by voltage in D600 suggests that release in small events provides the trigger Ca2+ for activation of sparks.

“…The final series of experiments demonstrated that perchlorate antagonized the actions of tetracaine in altering the available quantity, Qmax, but not the voltage sensitivity, k, of the qã charge. Millimolar tetracaine concentrations are known to inhibit contractile activation in skinned fibres, prevent Ca¥ release in triad preparations and block sarcoplasmic reticular RyR-Ca¥ channels in lipid bilayers (Antoniu, Kim, Morii & Ikemoto, 1985;Bull & Marengo, 1990;Xu et al 1993). They also reduced both the sustained phase of cisternal Ca¥ release observed in voltage-clamped fibres (Pizarro et al 1992) and abolished the qã charge in a study that attributed these actions to changes in a RyR coupled to the voltage sensor (Huang, 1997).…”

Section: Discussionmentioning

confidence: 99%

“…Bilayer studies have suggested that millimolar tetracaine concentrations block Ca¥ release channels of the sarcoplasmic reticulum (Xu, Jones & Meissner, 1993). Furthermore, the steady-state actions of tetracaine upon both the qã charge and the sustained phase of sarcoplasmic reticular Ca¥ release (Pizarro, Csernoch, Uribe & Rios, 1992) have recently been identified with an action through a RyR in turn coupled directly to a DHPR (Huang, 1997).…”

Section: ------------------------------------------------------------mentioning

confidence: 99%

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

Huang

1998

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...