Ionic metabolism in the horizontal cells of the retina

: According to the experimental data, the membrane potential of L-type horizontal cells in the bright light (i.e. when the input synapses are completely closed) is close to the potassium equilibrium potential. Basing on this fact the intracellular concentrations of K+ and Na+ ions are estimated. The latter proved to be relatively high (several tens mM) and comparable with intracellular concentration of potassium ions. This result in combination with the proximity of the light response equilibrium potential to zero level demonstrates that not only sodium conductance of a synaptic membrane but also potassium one take part in generation of light response. It is shown that stationary sodium and potassium synaptic currents are relatively weak and their variation within a working range of the membrane potentials (from -72 to -16 mV) is rather small. This stabilization of synaptic currents results from nonlinear properties of a nonsynaptic membrane of horizontal cells.