| Abstract No.: | A-B1051 |
| Country: | Canada |
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| Title: | FEEDBACK RESPONSES OF GOLDFISH HORIZONTAL CELLS MODULATED BY AMINOSULFONATE BUFFERS |
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| Authors/Affiliations: | 1 Stuart Trenholm*; 1 William H. Baldridge;
1 Dalhousie University, Halifax, NS, Canada
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| Content: | Objectives: By way of light-induced negative feedback, retinal horizontal cells (HCs) have been shown to contribute to the center-surround receptive field of cones (Baylor et. al, 1971). The cause of this feedback is still unknown. One theory posits that proton buffering in the synaptic cleft between cones and HCs is responsible for modulating feedback (Hirasawa & Kaneko, 2003; Vessey et al., 2005; Cadetti & Thoreson, 2006). Another explanation is that proton buffers, namely aminosulfonates like HEPES which are frequently used in such studies, directly affect hemichannels on the HC dendrites (Kammermans et al., 2001). To test these hypotheses we examined the effect of different aminosulfonate buffers, of differing pKa, on the light induced feedback responses of goldfish HCs.
Materials and Methods: Adult goldfish (Carassius auratus) eyes were enucleated. The anterior portion of the eye, including the lens, was removed. Eyecups were inverted onto filter paper and the optic nerve was severed to free the retina. The retina was transferred to a chamber which was superfused with bicarbonate Ringer’s solution (pH 7.4) in the dark before recordings commenced. Horizontal cell responses were elicited by full field light stimulation. Feedback was assessed from the rollback of the horizontal cell response during stimulation. Aminosulfonate buffers were added directly to the Ringer’s solution at a concentration of 20 mM with the pH adjusted to 7.4. These buffers included PIPES (pKa 6.8), MOPS (pKa 7.2), HEPES (pKa 7.5) and CHES (pKa 9.3).
Results: Rollback of the light-induced HC response was reversibly eliminated in the presence of aminosulfonate buffers PIPES, MOPS and HEPES. Rollback was not eliminated by CHES. Furthermore, rollback eliminated by HEPES could be restored with CHES.
Conclusion: Rollback was eliminated only by aminosulfonate buffers which had a pKa near the retina’s physiological pH. This suggests that pH buffering of the cone-HC synapse is more important in HC mediated feedback than a direct physical effect of aminosulfonate buffers on HC hemichannels. |
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