A superfusion system designed to measure release of radiolabeled neurotransmitters on a subsecond time scale

A new method for subsecond measurement of release of neurotransmitters from nerve terminal preparations (e.g., synaptosomes) in vitro is described. Synaptosomes were prelabeled with [3H]GABA via a Na-dependent GABA uptake system. The prelabeled nerve terminals are retained on small glass fiber filters in a superfusion chamber accessed by three high speed, solenoid-driven valves. Microcomputer-programmed circuitry controls the timing of valve operation. Each valve controls the delivery of a separate solution to the chamber, permitting rapid and independent control of membrane potential, [Ca2+]e, and drug delivery. The minimal dead volume of the chamber and the relatively high solution flow rate afford time resolution for release of at least 60 ms. This time resolution was necessary to observe the most rapid of at least three components of GABA release.