Neurotransmitter release can be measured by determining the amplitude of the postsynaptic potential after triggering an action potential in the presynaptic neuron.  Measuring neurotransmitter release this way can be problematic because the effect of the postsynaptic neuron to the same amount of released neurotransmitter can change over time.  Another way is to measure vesicle fusion with the presynaptic membrane directly using a patch pipette.  A cell membrane can be thought of as a capacitor in that positive and negative ions are stored on both sides of the membrane.  The larger the area of membrane the more ions that are necessary to hold the membrane at a certain potential.  In electrophysiology this means that a current injection into the terminal will take less time to charge a membrane to a given potential before vesicle fusion than it will after vesicle fusion.  The time course to charge the membrane to a potential and the resistance of the membrane is measured and with these values the capacitance of the membrane can be calculated by the equation Tau/Resistance=Capacitance.  With this technique researchers can measure synaptic vesicle release directly by measuring increases in the membrane capacitance of the presynaptic terminal.