<unk> s are a class of membrane transport proteins that span the cellular membranes of neurons. Their primary function is to carry<unk> s across these membranes and to direct their further transport to specific intracellular locations. There are more than twenty types of<unk> s. Vesicular<unk> s move<unk> s into synaptic vesicles, regulating the concentrations of substances within them. Vesicular<unk> s rely on a proton gradient created by the hydrolysis of adenosine triphosphate (ATP) in order to carry out their work: v-ATPase hydrolyzes ATP, causing protons to be pumped into the synaptic vesicles and creating a proton gradient. Then the efflux of protons from the vesicle provides the energy to bring the<unk>  into the vesicle.<unk> s frequently use electrochemical gradients that exist across cell membranes to carry out their work. For example, some<unk> s use energy obtained by the cotransport, or symport, of Na+ in order to move glutamate across membranes. Such neurotransporter cotransport systems are highly diverse, as recent development indicates that uptake systems are generally selective and associate with a specific<unk> . Normally,<unk> s in the synaptic membrane serve to remove<unk> s from the synaptic cleft and prevent their action or bring it to an end. However, on occasion<unk> s can work in reverse, transporting<unk> s into the synapse, allowing these<unk> s to bind to their receptors and exert their effect. This "nonvesicular release" of<unk> s is used by some cells, such as amacrine cells in the retina, as a normal form of<unk>  release.
Neurotransmitter transporter
Glutamate transporter
Norepinephrine transporter
Vesicular monoamine transporter
Cyclic nucleotide–gated ion channel
Vesicular monoamine transporter 1
Voltage-gated ion channel
Mechanosensitive channels