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

Abstract

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.

Fade of the response to prolonged glutamate application in the rat hippocampal slice

“…Similar desensitization to GLU and QUIS has been documented in locust postsynaptic muscle (Anis et al, 1981 ). Desensitization to GLU remains evident despite reduction of extracellular calcium concentration (Thieffry, 1984). This finding is concordant with our present results documenting that the fade of the depolarizing response to GLU in the hippocampus does not require the presence of extracellular calcium or synaptic transmission.…”

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

“…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).…”

Neuromodulator octopamine attenuates extrajunctional glutamate sensitivity in insect muscle

“…2A,B). Distinct responses to bathapplied and iontophoretically-applied L-glutamate have been reported for the crayfish neuromuscular junction: using this crustacean preparation, a reduction in external Ca2+ potentiated desensitization, thereby attenuating membrane responses to bath-applied L-glutamate with negligible effect on glutamate potentials [17]. Suppression by low-Ca2+ solution of the response to iontophoretically-applied glutamate was uncovered by measuring the time-course of recovery from desensitization with the double-pulse protocol [17].…”