Ion currents, mediated by GABAa-receptors in outside-out membrane patches, may alter the concentration of Chloride ions inside the pipette and the membrane patch.
GABAa-receptors are in fact ionotropic synaptic receptors, selective to Chloride ions. Therefore, chloride fluxes across the membrane patch correlate to GABAa-receptor opening.
Chloride ions accumulation, depletion and diffusion, inside the pipette and the membrane patch, affect by definition the Chloride equilibrium (i.e. Nernst) electrical potential. This in turn changes the ionic driving force underlying GABAa-mediated currents.
It follows that, in case of very small volumes and confined geometries, voltage-clamp recordings of GABAa-receptor currents carry information on both i) Chloride diffusion and ii) receptor kinetics.
The relevance of (i) and (ii) have been studied numerically by defining a 1-dimensional biophysical model, released here to the interested user.
Moroni M, Biro I, Giugliano M, Vijayan R, Biggin PC, Beato M, Sivilotti LG (2011) Chloride ions in the pore of glycine and GABA channels shape the time course and voltage dependence of agonist currents. J Neurosci 31:14095-106 [PubMed]