Abstract
P 083
Chelation of divalent cations by tricine and its effect on retinal signalling in control mice and in mice lacking the Ni2+-sensetive voltage-gated Ca2+-channels Cav2.3 and Cav3.2.
Maged Alnawaiseh1, Walid Albanna1, Chien-Chang Chen2, Kevin Campbell2, Matthias Lüke3, Toni Schneider1
1Institut für Neurophysiologie, Klinikum der Universität zu Köln, Köln, 2Physiology and Biophysics, The University of Iowa College of Medicine, Iowa City, USA, 3Klinik für Augenheilkunde, Campus Lübeck, Universitätsklinikum Schleswig-Holstein, Lübeck
Objective
Voltage-gated Ca2+-channels, which are sensitive to divalent cations (Ni2+, Zn2+) are involved in re-ciprocal retinal signalling in the bovine retina. As at least two high-affinity voltage-gated Ca2+-channels are known to be antagonized by micromolar Ni2+-concentrations, both of them were inacti-vated, and the isolated and superfused retina was used for ERG-recording under scotopic conditions.
Methods
Isolated murine retinas were mounted in a temperature-controlled recording chamber and perfused with an oxygen-saturated standard solution. Electric field potentials were recorded using Ag/AgCl-electrodes, to obtain the full ERG after each flash of light. Changes of the b-wave amplitude before, during and after drug application were calculated and plotted.
Results
During the equilibration of the isolated bovine retina to a buffer solution, which contained 15 mM sodium phosphate as the main pH-buffer component, a continuous increase of the b-wave amplitude was observed, when the equilibration period was extended beyond the standard equilibration time of 90-120 min. As in retinal synapses divalent cations (e.g.Zn2+-) are cosecreted during transretinal sig-nalling, a stable starting conditions to reach equal b-wave responses was achieved by adding 2.5 mM tricine in the presence of 12.5 mM sodium phosphate as a combined pH-buffer and chelation system. For the murine isolated and superfused retina the conditions for recording a stable b–wave re-sponse were further optimized and compared for control mice, for Cav2.3 and Cav3.2–deficient as well as for double knockout mice. Both, the initial shape of the ERG before adding NiCl2 as well as the change of the b-wave response upon NiCl2 application (15 µM) differed to a great extent.
Conclusions
Voltage-gated Ca2+-channels may contribute not only to basal transretinal signalling but also to recip-rocal signalling via voltage-gated Ca2+-channels sensitive to micromolar concentrations of divalent heavy metal cations.
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