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S. Trenholm, W. H. Baldridge; Effect of Aminosulfonate Buffers on Feedback Responses of Goldfish Retinal Horizontal Cells. Invest. Ophthalmol. Vis. Sci. 2008;49(13):2427.
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A number of studies have suggested that buffering protons reduces or blocks horizontal cell to cone feedback (Hirasawa & Kaneko, 2003; Vessey et al., 2005; Cadetti & Thoreson, 2006). An alternative explanation is that proton buffers directly modulate hemichannels on the dendrites of horizontal cells (Kamermans et al., 2001). If this is the case then it follows that proton buffers might have differential effects on feedback independent of their capacity to buffer protons (pKa). To address this issue we tested the effect of aminosulfonate proton buffers, of different pKa, on the feedback responses of goldfish horizontal cells.
Adult goldfish (Carassius auratus) eyes were enucleated and the anterior portion of the eye was removed including the lens. Eyecups were inverted onto a piece of filter paper and the optic nerve was severed to free the retina. The retina was transferred to a chamber and 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).
Rollback of the horizontal cell response was reversibly eliminated in the presence of the aminosulfonate buffers PIPES, MOPS and HEPES. CHES did not eliminate horizontal cell rollback. In some retinas the sequential effect of HEPES and CHES was tested. In these retinas HEPES consistently blocked rollback but during subsequent superfusion with CHES rollback was restored.
Each of the aminosulfonate buffers with a pKa near 7.4 (PIPES, MOPS and HEPES) abolished the rollback of the horizontal cell response. While this does not rule out the possibility that PIPES, MOPS and HEPES, but not CHES, modulate hemichannels, the results are consistent with the predicted proton buffering capacity of these agents.
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