The Initiation of Spike Potential in Barnacle Muscle Fibers under Low Intracellular Ca++

SUMMARY1. The cation composition of single barnacle muscle fibres following damage by axial insertion of a microsyringe has been measured. The Na and Ca contents of these fibres were raised.2. Electronmicroscopic studies of fibres following insertion of a microsyringe indicated that the damage done resulted in tubular obstruction of the T-system.3. Fibres loaded with radiosodium by micro-injection showed that the Na* efflux declined exponentially with time, but that in most fibres the Injections of distilled water deep in the fibre failed to influence the course of the Na* efflux.4. K removal reduced the Na efflux by 47 %. However, a few fibres displayed very little K-dependence.5. When measured in fibres already soaked in a K-free medium for long periods the sodium efflux consisted of a brief rapid phase, followed by a slow phase of Na loss.6. In the presence of 30 mM-K, there was little or no rise in the Na efflux. Raising the external K to 50 or 100 mm caused a marked rise in the Na efflux. Raising the external K to 30 mm in the absence of external Ca2+ led to a rise in the Na efflux. A high K solution always caused shortening of these fibres.7. Internal application of 1 M or 1 mM-CaCl2 often caused a significant rise in the Na efflux.8. Internal application of 2x5 or 5 M saline caused a prompt and large t Permanent address: Institute of Physiology and Medical Biophysics, University of Uppsala, Uppsala, Sweden. E. EDWARD BITTAR AND OTHERS fall in the Na efflux. In the presence of high K saline-loaded fibres failed to contract.9. Internal application of 0-5 M-ATP stimulated the Na efflux. A larger effect was not observed in fibres pre-treated with 2 M-MgCl2. Internal application of 0 5 m-ArP was without effect.10. The results indicate that the barnacle fibre is a suitable preparation for the study of Na fluxes by means of the micro-injection technique. They also indicate that the mechanism regulating the Na efflux is not quite the same as that found in squid axon or frog muscle.

Section: Resultsmentioning

confidence: 99%

An investigation of sodium transport in barnacle muscle fibres by means of the microsyringe technique

Bittar¹,

Chen²,

Danielson³

et al. 1972

“…4B). The possibility of such blocking action of internal Ca was shown by Hagiwara & Naka (1964) in the barnacle muscle fibres. Injections of Ca-EGTA buffers into this tissue showed that the internal free Ca concentration should be below 8 x 1o-8 M in order to produce a Ca-dependent action potential (Hagiwara & Nakajima, 1966).…”

Section: Discussionmentioning

confidence: 96%

Effects of calcium and calcium‐chelating agents on the inward and outward current in the membrane of mollusc neurones

Kostyuk¹,

Krishtal²

1977

270

128

SUMMARY1. Effects of internal and external Ca and Ca-chelating agents, EGTA and EDTA on transmembrane ionic currents were studied in isolated, internally dialysed neurones from the molluscs, Helix pomatia and Limnea stagnalis.2. The possible pharmacological effect of internally applied EGTA was investigated on the background of constant free Ca concentration (5-3 x 10-9 M). EGTA had no effect on Ca and Na inward currents but considerably depressed the delayed K outward current. No effective removal of this action could be achieved by the elevation of intracellular free Ca.3. In the absence of divalent cations in the external medium, EGTA (as well as EDTA) applied either intra-or extracellularly caused the appearance of a very large Na inward current with kinetics similar to those of Ca inward current and with the reversal potential around 10 mV. Effective concentrations of chelating agents were 041 mm (extracellular) and 1-0 mm (intracellular).4. Increase in intracellular Ca in the absence of EGTA (by dialysis of the cell with Ca-saturated solutions) did not produce any significant effect on the delayed K outward current. The small change observed in this current could be evaluated as a depression of maximum slope conductance and a shift to more negative membrane potential.5. Ca inward current has been found extremely sensitive to internal Ca. 5-8 x 108 M of internal free Ca produced its complete depression. This effect was reversible. Na inward current could be inhibited with 3-5 x 10-7 M intracellular Ca.

“…The calcium conductance attains maximum values when the intracellular concentration of Ca2+ is very low (Hagiwara & Naka, 1964;Kostyuk & Krishtal, 1977b). This was achieved in the present experiments by adding 5 mM-EGTA to the intracellular solution.…”

Section: Separation Of Two Components Of the Asymmetric Displacement mentioning

confidence: 99%

Calcium inward current and related charge movements in the membrane of snail neurones.

Kostyuk¹,

Krishtal²,

Pidoplichko³

1981

SUMMARY1. Isolated and intracellularly perfused neurones from the snail Helix pomatia have been investigated under voltage-clamp conditions. Calcium inward current and asymmetric displacement current were examined.2. Two components of the asymmetric displacement current have been distinguished. One of them was irreversibly blocked by intracellular fluoride together with the calcium inward current. Another component (about 20 %) was not affected. The relation of the fluoride-sensitive asymmetric displacement current to the activity of calcium channels was investigated.3. The amounts of charge displaced by the on-and off-responses of the asymmetric current were similar. The maximum charge displacement was between 1500 and 2000 electron charges/ILm2.4. The normalized steady-state voltage distribution curve of the displaced charge coincided with the square root of the normalized calcium conductance. The slope was 4 mV per e-fold change for the calcium conductance and 8 mV for the charge distribution. Thus, the effective valencies were close to 6 (for the calcium conductance) and 3 (for the charge distribution), suggesting two gating particles per calcium channel.5. The on-process of the calcium inward current fitted m2 kinetics. The time constant Tm corresponded to the time constant T" of the asymmetric current in a wide range of tested voltages. This correspondence failed only at small depolarizations where Tm exceeded Ton.6. The 'off' time constants of the calcium inward current (-rCa) and the asymmetric current (FrO) examined at -40 mV did not depend significantly on the test pulse height. The ratio Ta" /Trc varied between 1I7 and 2 5.7. Calcium inward-current relaxation kinetics were measured for small shifts of membrane potential (Vtest = -2 mV) applied at the peaks of the current. The time constants were smaller than Tm and depended only weakly on voltage. 8. It is concluded that the fluoride-sensitive asymmetric displacement current is related to the activation of calcium channels.