Ways to discern the presynaptic effect of drugs on neurotransmitter release

This study is based on the authors' theory for neurotransmitter release in which explicit recognition is given to the generally accepted hypothesis that intracellular calcium ions (Ca) control the release. The new theory considers the resting level of intracellular Ca and proposes a saturating equation for the entry of Ca into the nerve terminals. The main purpose of the present paper is, by applying the new theory, to suggest experimental methods for discerning the various possible effects of drugs on release. New interpretations are given of log-log graphs of release as a function of extracellular Ca concentration. Maximal facilitation and the duration of facilitation are two other measurements that are shown to be particularly useful in determining the nature of drug action.