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Manipulation of synaptic sign and strength with divalent cations in the vertebrate retina: pushing the limits of tonic, chemical neurotransmission
Author(s) -
Piccolino Marco,
Vellani Vittorio,
Rakotobe Liramalala A.,
Pignatelli Angela,
Barnes S.,
McNaughton Peter
Publication year - 1999
Publication title -
european journal of neuroscience
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.346
H-Index - 206
eISSN - 1460-9568
pISSN - 0953-816X
DOI - 10.1046/j.1460-9568.1999.00842.x
Subject(s) - neurotransmission , divalent , neurotransmitter , biophysics , synaptic cleft , neuroscience , chemistry , synapse , tonic (physiology) , postsynaptic potential , synaptic vesicle , biology , receptor , biochemistry , membrane , vesicle , organic chemistry
At the first synaptic level of the vertebrate retina, photoreceptor light responses are transmitted to second order neurones through a chemical synapse based on a tonic release of neurotransmitter modulated by graded changes of presynaptic potential. The possibility that such synapses could work through a Ca 2+ ‐independent process had been proposed by previous authors, based on the persistence of transmission process in low Ca 2+ media containing Co 2+ or Ni 2+ ions. Recently, we were able to explain these results within the framework of the classical calcium‐hypothesis of synaptic transmission by taking into account the modifications of presynaptic surface potential brought about by changes of divalent cation concentrations. Here we report data showing how a surface‐charge hypothesis could account for several apparently paradoxical effects of divalent cation manipulations such as: the enhancement of neurotransmitter release induced by low Ca 2+ media; the transmission "unblocking" effect of Zn 2+ , Co 2+ and Ni 2+ ; and the reversal of transmission polarity induced by application of low Ca 2+ media containing Cd 2+ or Mg 2+ ions.