Chloride dynamics alter the input-output properties of neurons
Fig 1
Optogenetic quantification of chloride extrusion in hippocampal neurons.
(A) Left, schematic of the experimental setup where a gramicidin perforated patch is made from an eNpHR-expressing hippocampal pyramidal neuron. Green light is delivered via the objective and GABA puffs (blue) directed at the cell soma. Right, top, gramicidin perforated patch voltage-clamp recording from a neuron expressing eNpHR3.0-EYFP. GABAAR currents recorded at different times, on different trials following 15s of Cl- load induced by light activation of eNpHR. Right bottom, EGABA and [Cl-]i were calculated from each GABAAR current (squares, see Methods) and plotted as a function of time after the photocurrent for a single cell. [Cl-]i recovery was fitted by a single-exponential function (black). (B) From the data in ‘A’, KCC2 Cl- extrusion rate (V) as a function of [Cl-]i was calculated. This allowed for the Cl- extrusion constant, P, to be calculated. (C) Population data from 8 neurons resulted in an average value of P of 0.001 mM-1 · s-1. A single compartmental model was then created using the NEURON simulation environment. By accounting for Cl- dynamics including Cl- extrusion via KCC2, a Cl- recovery curve and simulated GABAAR currents could be generated (orange curves in ‘A’). These closely match our experimental data.