In previous worli Piccolino at cl, PNAS, l996; Piccolino and Pignatelli, TINS, 1996) we provided evidence suggesting that the increase of synaptic transmitter release from PR synapses induced by application of nominally Ca2+•free solution was the consequence of a paradoxical increase of [Ca2+]i in PRs consequent to increased opening of Ca2+ channels via a surface- charge mediated. In order to support our interpretation, in the present study we measured, in retina eyecup preparations, the changes of [Ca2+]o induced by alpplication of nominally Ca2+-free media by using micropipettes it ed with a Ca2+ ionophore, and, moreover, we measured, by using (FLUO-3 AM), the changes of [Ca2+]i induced in isolated PRs by bath application of Ca2+ concentrations comparable to those induced in eyecups by nominally Ca2+ free media. In eyecups superfused from the vitreal side with nominally Ca2+-free media for periods of 30 minutes or more, [Ca2+]o near the PH terminals decreased to levels of 1.5- 0.5 mM. During Ca2+-free application, clear spatial gradients of [Ca2+]o were evident along the sclero-vitreal axis with lower [Ca2+]o near the vitreal surface. Membrane depolarisation induced in isolated PRs by solutions containing elevated [K+] (15 mM} and normal (3 mM) [Ca2+] resulted in an increase of [Ca2+], as monitored with Ca2+-imaging technique. When the same high K+ solutions were applied in the presence of reduced [Ca2+] (0.7-0.3 mM) the increase of [Ca2+], signal was enhanced. These results iustify our "surfaee-charge" interpretation of the transmitter release changes induced by low Ca2+ application in eyecup preparations, and invite caution in interpreting the effects of low Ca2+ media in intact or semi-intact preparations of the nervous system.
LOW EXTRACELLULAR Ca2+ ENHANCES SYNAPTIC TRANSMITTER RELEASE FROM ` RETINAL PHOTORECEPTORS (PRs) BY INCREASING PRESYNAPTIC INTRACELLULAR [Ca2+] IN PR
PICCOLINO, Marco;PIGNATELLI, Angela;
1998
Abstract
In previous worli Piccolino at cl, PNAS, l996; Piccolino and Pignatelli, TINS, 1996) we provided evidence suggesting that the increase of synaptic transmitter release from PR synapses induced by application of nominally Ca2+•free solution was the consequence of a paradoxical increase of [Ca2+]i in PRs consequent to increased opening of Ca2+ channels via a surface- charge mediated. In order to support our interpretation, in the present study we measured, in retina eyecup preparations, the changes of [Ca2+]o induced by alpplication of nominally Ca2+-free media by using micropipettes it ed with a Ca2+ ionophore, and, moreover, we measured, by using (FLUO-3 AM), the changes of [Ca2+]i induced in isolated PRs by bath application of Ca2+ concentrations comparable to those induced in eyecups by nominally Ca2+ free media. In eyecups superfused from the vitreal side with nominally Ca2+-free media for periods of 30 minutes or more, [Ca2+]o near the PH terminals decreased to levels of 1.5- 0.5 mM. During Ca2+-free application, clear spatial gradients of [Ca2+]o were evident along the sclero-vitreal axis with lower [Ca2+]o near the vitreal surface. Membrane depolarisation induced in isolated PRs by solutions containing elevated [K+] (15 mM} and normal (3 mM) [Ca2+] resulted in an increase of [Ca2+], as monitored with Ca2+-imaging technique. When the same high K+ solutions were applied in the presence of reduced [Ca2+] (0.7-0.3 mM) the increase of [Ca2+], signal was enhanced. These results iustify our "surfaee-charge" interpretation of the transmitter release changes induced by low Ca2+ application in eyecup preparations, and invite caution in interpreting the effects of low Ca2+ media in intact or semi-intact preparations of the nervous system.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
