ASYNCHRONOUS TRANSMITTER RELEASE - CONTROL OF EXOCYTOSIS AND ENDOCYTOSIS AT THE SALAMANDER ROD SYNAPSE

1. We have studied exocytosis and endocytosis in the synaptic terminal of salamander rods using a combination of Ca2+ imaging, capacitance m easurement and the photolysis of Ca2+ buffers. 2. The average cytoplas mic Ca2+ concentration at the dark resting potential was 2-4 mu M. 3. An average cytoplasmic Ca2+ concentration of 2-4 mu M maintained a hig h rate of continuous exocytosis and endocytosis. 4. Changes in the rat e of exocytosis were followed in less than 0.7 s by compensatory chang es in the rate of endocytosis. 5. Vesicle cycling in the rod synapse i s specialized for graded transmission and differs from that previously described for synapses that release synchronized bursts of transmitte r.