Calcium role in depolarization-secretion coupling: an aequorin study in squid giant synapse.
- 1 January 1975
- journal article
- Published by Proceedings of the National Academy of Sciences in Proceedings of the National Academy of Sciences
- Vol. 72 (1), 187-190
- https://doi.org/10.1073/pnas.72.1.187
Abstract
Aequorin, a protein that emits light in the presence of calcium, was injected in the presynaptic terminal of the squid giant synapse. This injection was preceded by intracellular tetraethylammonium administration, which prolonged the duration of the presynaptic action potential. After this procedure light emission was evoked by single presynaptic spikes capable of releasing synaptic transmitter. In a second set of experiments, presynaptic tetraethylammonium injection was followed by the administration of tetrodotoxin extracellularly, which abolished the presynaptic action potential. Under these conditions artificial depolarization of the presynaptic terminal triggered the release of synaptic transmitter, in a graded manner. However, as previously reported by other authors, membrane potential steps to an internal positive value of approximately plus 90 mV (the suppression potential) produced a blockage of transmitter release for the duration of the imposed potential. Synaptic transmission recurred, nevertheless, as the current injection was terminated. A similar set of experiments, performed after the intracellular injection of aequorin in the presynaptic fiber, demonstrated that the aequorin light response was evoked by membrane potential steps capable of releasing synaptic transmitter. If the membrane potential was made positive to the "suppression" level, no light response was evoked but the light emission appeared, as did transmitter release, at the end of the current pulse. These experiments demonstrate that release of transmitter is directly correlated with intracellular calcium concentration and that the suppression potential is compatible with the existence of a calcium equilibrium potential at the presynaptic terminal.Keywords
This publication has 24 references indexed in Scilit:
- The interrelationship between sodium and calcium fluxes across cell membranesReviews of physiology, biochemistry and pharmacology, 1973
- Control of muscle contractionQuarterly Reviews of Biophysics, 1969
- Response of Aequorin Bioluminescence to Rapid Changes in Calcium ConcentrationNature, 1969
- Correlation of Transmitter Release with Membrane Properties of the Presynaptic Fiber of the Squid Giant SynapseThe Journal of general physiology, 1967
- Transmitter Release at the Squid Giant Synapse in the Presence of TetrodotoxinNature, 1966
- Anomalous Rectification in the Squid Giant Axon Injected with Tetraethylammonium ChlorideThe Journal of general physiology, 1965
- Electrical Changes in Pre- and Postsynaptic Axons of the Giant Synapse of Loligo The Journal of general physiology, 1962
- Extraction, Purification and Properties of Aequorin, a Bioluminescent Protein from the Luminous Hydromedusan, AequoreaJournal of Cellular and Comparative Physiology, 1962
- TRANSMISSION IN SQUID GIANT SYNAPSESThe Journal of general physiology, 1958
- INTRACELLULAR RECORDING FROM THE GIANT SYNAPSE OF THE SQUIDThe Journal of general physiology, 1957