Zinc attenuation of ERG a-wave response amplitude is reduced by histidine. The mean ΔVmax obtained from the relationship above fitted to each dataset for 75mM Na L-aspartate to which 100μM histidine had been added for 30 minutes is shown as a percent increase from the a-wave amplitude after 30 minutes in aspartate alone (left column, ±SEM, N=5). The mean ΔVmax of similar curves fitted to normalized responses recorded after adding 50μM zinc (middle column, ±SEM, N=4) or 50μM zinc plus 100μM histidine (right column, ±SEM, N=4) for the final 30 minutes following 40 minutes in aspartate show that the a-wave amplitude attenuation induced by zinc is reduced in the presence of histidine.