CNSforum The Lundbeck Institute

Brain physiology: Neurotransmisson Basics

The Na+/K+ ATPase

Na+/K+ ATPase is a pump that uses the energy from the hydrolysis of ATP to actively pump sodium and potassium ions against their concentration. The binding of three sodium ions to internal binding sites on the cytoplasmic side of the pump and phosphorylation of the pump induces a conformational change that releases the Na+ ions into the extracellular space. The subsequent binding of two potassium ions to the pump within the synapse followed by dephosphorylation causes it to return to its original confirmation and release the potassium ions into the cytoplasm. This pump is found in almost all cells of the body and the ionic gradient that it creates is used to carry out numerous important cellular processes, such as the transport of other molecules across membrane eg the monoamines.

Fusion of a synaptic vesicle with the pre-synaptic membrane

Neurones communicate with their target cells primarily through the regulated fusion of synaptic vesicles with the nerve terminal membrane and subsequent release of chemical neurotransmitter into the synaptic cleft. Synaptic vesicles move down the axon and bind to release sites on the pre-synaptic membrane via vesicle-membrane proteins (v-SNARE) and target-membrane proteins (t-SNAREs). This SNARE complex interacts with both NSF (N-ethylmaleimide Sensitive Fusion protein) and SNAP (Soluble NSF Attachment Proteins) to form a fusion complex. Action potential propagation induces calcium influx at the pre-synaptic membrane, which, in addition to ATP hydrolysis by NSF, results in disassembly of the SNARE complex and membrane fusion. Following neurotransmitter release, synaptic vesicle membrane components are recycled via an endocytic process.