The effects of calcium at the crayfish neuromuscular junction

Nickell, William T.; Boyarsky, L. L.

doi:10.1016/0300-9629(80)90160-7

Cited by 13 publications

(6 citation statements)

References 12 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Thus, Ca2+ does not affect the number of activatable receptors and acts only on the activated glutamate receptor-channel complex. The above results contrast with those of previous studies (Thieffry & Bruner, 1978;Nickell & Boyarsky, 1980) where the reduction of external Ca2+ concentration was shown to block ionophoretic responses much more strongly than found in the present case. Such a discrepancy can be attributed to the better control of agonist leakage achieved in the present study by use of high resistance pipettes (see Dudel, 1975a, b).…”

Section: Discussioncontrasting

confidence: 99%

“…None of the divalent ions (Mg2+, Sr2+, Ba2+, Mn2+ or Co2+) can overcome even partially the faster fading of the glutamate response in low Ca2+ solutions (Onodera & Takeuchi, 1976;Ashley & Campbell, 1978;Nickell & Boyarsky, 1980;Thieffry, 1982). This eliminates the possibility that Ca2+ simply acts by screening surface charges.…”

Section: Discussionmentioning

confidence: 99%

“…Since Na+ is by far the major cation in crustacean physiological solutions, reducing the normal concentration of Ca2+ would not be expected to have a marked effect on the amplitude of the glutamate response. However, several investigations revealed that decreasing external Ca2+ considerably reduces the glutamate response, a phenomenon referred to below as the Ca2+ dependence of the response (Onodera & Takeuchi, 1976;Ashley & Campbell, 1978;Thieffry & Bruner, 1978;Nickell & Boyarsky, 1980). In contrast, the response to single quanta of the natural transmitter are less affected (Thieffry & Bruner, 1978;Dudel, 1981).…”

Section: Introductionmentioning

confidence: 99%

“…In contrast, the response to single quanta of the natural transmitter are less affected (Thieffry & Bruner, 1978;Dudel, 1981). This dependence on Ca2+ is specific, since compensating for the lowered Ca2+ concentration with other divalent cations does not impede the effect of a reduction in external Ca2+ (Onodera & Takeuchi, 1976;Ashley & Campbell, 1978;Nickell & Boyarsky, 1980). In fact, adding other divalent cations or increasing the Ca2+ concentration causes a depression in the glutamate response, presumably by an action of these ions at the channel level (Barker, 1975).…”

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

The effect of calcium ions on the glutamate response and its desensitization in crayfish muscle fibres.

Thieffry¹

1984

The Journal of Physiology

View full text Add to dashboard Cite

SUMMARY1. The responses of crayfish muscle fibres to bath application or long ionophoresis of L-glutamate were studied in normal and low Ca2+ solutions.2. The smaller responses recorded in low Ca2+ solutions have characteristics suggesting a faster desensitization.3. Desensitization and recovery have complex kinetics. Desensitization is faster and recovery slower when external Ca2+ concentration is reduced. Both components of the recovery phase, which can be fitted by the sum of two exponential, are affected by the external Ca2+ concentration.4. Recovery can be accelerated by external Ca2+ ionophoresis onto desensitized glutamate receptors.5. Responses to brief glutamate pulses of low intensity are not affected by Ca2+ reduction. For higher intensities, signs of desensitization are detectable early in the rising phase of the response.6. Concanavalin A (Con A) blocks both desensitization and Ca2+ dependence with similar time courses.7. Whether or not the preparation has been treated with Con A, the slowly rising responses recorded in isotonic Ca2+ do not show signs of desensitization.8. Con A causes a partial blockade of the glutamate response. 9. The Ca2+ dependence of the glutamate response can be explained by the Ca2+ dependence of the desensitization process, the cation acting at ectocellular sites of the muscle membrane.

show abstract

Section: Discussioncontrasting

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

The effect of calcium ions on the glutamate response and its desensitization in crayfish muscle fibres.

Thieffry¹

1984

The Journal of Physiology

View full text Add to dashboard Cite

show abstract

“…One possibility is that 'co-operativity' at the squid synapse results from a non-linear relationship between transmitter release and post-synaptic response. For example, post-synaptic sensitivity to the transmitter could change with [Ca]o (Onodera & Takeuchi, 1976;Nickell & Boyarsky, 1980;Dudel, 1981;Thieffry, 1984), but this explanation seems unlikely because Katz & Miledi (1970) have reported that spontaneous miniature post-synaptic potentials recorded at squid synapses are little affected by changes in [Ca]0. Nevertheless, if the post-synaptic response is a high-order function of transmitter concentration and if quantal release events spatially overlap on the postsynaptic membrane, post-synaptic non-linearities might still occur (Hartzell, Kuffler & Yoshikami, 1975).…”

Section: Measurement Of Presynaptic Ca Currentmentioning

confidence: 99%

Calcium dependence of presynaptic calcium current and post‐synaptic response at the squid giant synapse.

Augustine¹,

Charlton²

1986

The Journal of Physiology

207

128

View full text Add to dashboard Cite

SUMMARY1. Neurotransmitter release has a non-linear dependence upon the external Ca concentration, [Ca].. This may be due to a 'co-operative' action of Ca in triggering release. The dependence of presynaptic Ca currents and post-synaptic currents (p.s.c.s) upon [Ca]. was examined at voltage-clamped 'giant' synapses of squid to determine whether this 'co-operativity' occurs during or after influx of Ca into the presynaptic terminal.2. Presynaptic Ca current was proportional to ([Ca]./(1 + [Ca]O/KD))n, where n, the order of the function, was roughly 1 and KD, the apparent dissociation constant for Ca, was approximately 80 mm.3. P.s.c.s also could be described by the same function, but had an n of 3-4 and a lower KD.4. These results suggest that the 'co-operative' action of Ca occurs at a step or steps beyond entry of Ca into the presynaptic terminal.5. Synaptic transfer curves relating presynaptic Ca currents, elicited by depolarizations to different potentials, to resultant p.s.c.s were power functions whose exponent depended upon [Ca].. Maximum exponents were as high as 4 at [Ca]

show abstract

Transmitter release in crayfish neuromuscular junction: Comments on the article by Staggs et al. (1980)

Parnas

Dudél²

1982

J. Neurobiol.

View full text Add to dashboard Cite

Recently, Staggs et al. (1980) reported that, in crayfish, excitatory postsynaptic potentials (EPSPs) measured at different extracellular calcium concentrations [Ca], are not affected by applied picrotoxin. This finding was interpreted to contradict the observation of Parnas, Rahamimoff, and Sarne (1975) that picrotoxin, by removing a tonic inhibition, leads to an increase of EPSPs. It is important to note that the latter results were obtained at the neuromuscular junction of a crab (Ocypode), while the findings of Staggs et al. (1980) were obtained at crayfish neuromuscular junctions and thus are not seen to "contradict," especially since their conditions were unfavorable for the observation of tonic inhibition. Staggs et al. (1980) also emphasized and gave evidence that in crayfish there is a linear dependence of the amplitude of the EPSP on [Ca],, as reported earlier (Bracho and Orkand, 1970;Ortiz and Bracho, 1972;Zucker, 1974). Since in vertebrate endplates this dependence is very nonlinear (d log EPSP)I(d log [Calo) = 4 (Dodge and Rahamimoff, 1967), and since this nonlinearity is a prerequisite for explaining the observed facilitation by the residual calcium mechanism, this apparent and "suspect" (Atwood, 1977) deviation of EPSP behavior in crayfish should not be left without comment. A recent report by Nickell and Boyarski (1980) showed a dependence of the excitatory postsynaptic current (EPSC) on [Ca];, as well as postsynaptic effects of [Ca], on the EPSC. Figure 1 shows examples of recordings of EPSCs at the neuromuscular junction of the crayfish (Astacus Zeptodactylus) abductor digiti primi at different [Ca],. The synaptic currents were measured at single synaptic spots by means of a patch clamp electrode (Neher, Sakmann, and Steinbach, 1978;Dudel, 1981). Average amplitudes of EPSCs from 19 experiments are plotted in Figure 2 (Fig. 4 from Parnas, Dudel, and Parnas, submitted). In this plot the amplitudes were corrected for postsynaptic effects of low [Ca],, since at 1.7mM [Calo the quantum size is about one-half of that at 13.5mM [Ca], (Dudel, 1981). The slope of the log EPSC to log [Ca], relationship in Figure 2 is 1.6. This slope would have been nearly 2, at low [Ca],, without correction of postsynaptic effects. This agrees with the findings of Nickell and Boyarski (1980), an extensive study of synaptic facilitation (Parnas et al., submitted), and on quantum content (Dudel, 1981) at different [Calo in the crayfish neuromuscular junction. Therefore, there is no reason to assume that the [Ca]o dependence of synaptic transmission, and more importantly, the mechanism of facilitation are basically different in crayfish and vertebrates.The consistent failure of Staggs et al. (1980) to observe nonlinearity may be explained by insufficient access of the low-[Calo solution to the synapses. We have found that careful removal of obstructing fine tissue layers, rapid super-

show abstract

The effects of calcium at the crayfish neuromuscular junction

Cited by 13 publications

References 12 publications

The effect of calcium ions on the glutamate response and its desensitization in crayfish muscle fibres.

The effect of calcium ions on the glutamate response and its desensitization in crayfish muscle fibres.

Calcium dependence of presynaptic calcium current and post‐synaptic response at the squid giant synapse.

Transmitter release in crayfish neuromuscular junction: Comments on the article by Staggs et al. (1980)

Contact Info

Product

Resources

About