Biophysical calibrations of a fluorescent biosensor to measure intracellular chloride in neurons and its biological application: an insight into diurnal oscillation of inhibitory system

Neuronal Network consists of two different types of neurons: the excitatory and inhibitory systems. They are like two faces of the same coin that must be perfectly balanced to avoid several pathologies and diseases. The inhibitory system is really fundamental in the modulation of the excitatory response, it influences the rhythms of the brain, synaptic plasticity and the flow of information in neuronal circuitry. The main inhibitory synaptic receptors are channels conducting chloride. These receptors are mostly activated by GABA , which is one of the most important inhibitory neurotransmitter. The effect of GABA in the postsynaptic cell depends directly from the value of the equilibrium potential of chloride calculated with the Nernst equation, that includes the logarithmic ratio of the extracellular and intracellular chloride. When the equilibrium potential of chloride is lower (more negative) than the resting membrane potential, the opening of the -channel leads to an influx of the ion and an hyperpolarization of the cell. When the equilibrium potential is less negative than the resting membrane potential the result will be translated in an efflux of the ion that depolarizes the cell. The intracellular concentration of chloride is regulated by two co-transporters : NKCC1 and KCC2 that are present at the level of the neuronal membrane. In the first period of development (