Ion Channels
Aquaporins also referred to as water channels, are proteins in the cell membrane that transports water across the cell membrane and allows cells to maintain osmotic pressure. The two main aquaporin molecules of the central nervous system, AQP1, and AQP4, control the volume of extracellular and intracellular fluid, respectively, and regulate the movement of brain water and CSF. They also play a role in cytotoxic and vasogenic oedema.
Calcium channels are transmembrane ion channels that are permeable to calcium ions. These channels can be controlled by ligand binding or voltage. Calcium regulates several neuronal functions, including neurotransmitter synthesis and release, neuronal excitability, phosphorylation, and other processes.
Potassium channels are transmembrane ion channels that selectively permit the flow of potassium ions down their electrochemical gradient. It is essential for regulating the action potential duration, firing frequency, neurotransmitter release, calcium signalling, and mitochondrial functions in neuronal cells, all of which are important for controlling the physiological processes in the brain, including membrane hyperpolarization and modulation.
These transmembrane proteins allow the non-selective passage of cations through the channel upon activation by cyclic nucleotides. Non-selective cation channels call cyclic nucleotide-gated (CNG) channels were first discovered in olfactory sensory neurons and retinal photoreceptors (OSNs). They are opened by the direct binding of cyclic nucleotides, cAMP, and cGMP.