Ionic movements in the isolated chicken retina during spreading depression.

The effects of adding tetrodotoxin, zinc, tetraethylammonium and manganese ions and the effects of the changes in calcium concentration in the bathing solution were studied upon the initiation and propagation of spreading depression waves elicited in the isolated chicken retina. The spreading depression (SD) was unaffected by tetrodotoxin in the concentrations used to block action potentials on axons. Tetraethylammonium and zinc ions had only a slight effect slowing the rate of propagation, an effect which was relieved by increasing the potassium or the calcium concentration. Zero calcium gave rise to the appearance of spontaneous waves of SD and a late loss of the excitability of the preparation. Low calcium concentrations slowed, and high concentrations increased, the rate of propagation. The late and prolonged increase in light reflectance was diminished under high calcium. Manganese blocked the responses. This blocking effect was antagonized by calcium simply by elevating its concentration above that of manganese.