Fast application of agonists to isolated membrane patches

At a synapse, the transmitter is stored in synaptic vesicles and is released into the synaptic cleft almost instantaneously upon fusion of these vesicles with the presynaptic membrane. Subsequently, the transmitter diffuses to ligand-gated ion channels in the postsynaptic density, binds to them, and thereby causes channel activation. Unfortunately, we have estimates neither of the exact amount of transmitter in the synaptic vesicle nor of the concentration in the synaptic cleft reaching the postsynaptic receptors, and in some cases even the identity of the transmitter is unknown. These questions may be addressed by modeling of release and diffusion. Such a theoretical approach, however, is based on several assumptions, some of which lack experimental evidence.