Retinal horizontal cells: old cells, old experiments, new results
Piccolino, M.; Pignatelli, A.; Sbrenna, L.
Archives Italiennes de Biologie 135(2): 111-129
1997
ISSN/ISBN: 0003-9829 PMID: 9101023 Document Number: 482399
The study of neural interactions in the vertebrate retina carried out after the pioneering studies of Svaetichin has provided important information on the functioning of nerve circuits in the central nervous system. Recently we have investigated the effects of changes of divalent cation concentration on the synaptic transmission between cones and horizontal cells of the turtle retina. Our results seemed apparently in contrast with the classical Ca-2+-hypothesis of chemical synaptic transmission. Application of low Ca-2+ media resulted in a recovery of synaptic transmission after application of divalent cations such as Ca-2+, Zn-2+ and Ni-2+ traditionally considered as Ca-2+ channel antagonists. Moreover, in the absence of exogenous divalent cations, low Ca-2+ could result in an increase of transmitter release particularly if Mg-2+ was omitted from the perfusing medium. These apparently paradoxical results can be reconciled with the postulates of the Ca-2+-hypothesis of synaptic transmission by taking into account the effects of divalent cations on the fixed charges present at the external surface of cell membrane. It is possible that a similar interpretation could also account for the so-called "Ca-2+-independent" transmission in other structures of the nervous system.