Fig. 7.

Conditions expected to deplete photoreceptors of histamine increase their uptake of [³H]histidine. Preparations were preincubated in high K⁺ (100 mm) to stimulate histamine release and chlorpromazine (20 μm) to decrease HA reuptake. After a 5 min wash in normal saline, preparations were incubated in 20 μm[³H]histidine under standard conditions. Somata of “depleted” preparations (n = 3) showed an increase in grain density over controls (n = 3). Each time point is the average of four to six areas counted within a photoreceptor soma for each preparation.