Figure 9. Alkalinization of the external solution abolished the ability of glutamate to alter H⁺ flux from horizontal cells.

A, recording from one cell bathed in a solution adjusted to have an extracellular pH of 9.5. Application of 300 μm glutamate now failed to alter H⁺ flux. B, measurement of fura-2 fluorescence to examine calcium increases in horizontal cells when bathed in Ringer solution at pH 9.5. Addition of kainate at 20 μm produced a sizable increase in the ratio of 334 nm/380 nm fluorescence, indicating a significant increase in intracellular calcium.