DIGITAL PROCESSING OF THE CURRENT NOISE EVOKED BY KAINATE IN CEREBELLAR GRANULE CELLS

Current induced in cultured cerebellar granule cells by the bath appli cation of kainate (500 mu M) was measured using the conventional patch -clamp technique. Two different kinds of responses were observed after the agonist perfusion. Some cells exhibited small inward whole-cell c urrents: 116 +/- 40 pA (7 cells) at a clamp potential of -60 mV; in ot her cells, the agonist induced significantly larger currents: 420 +/- 35 pA (6 cells) at a clamp potential of -60 mV. The current flowing in the agonist-activated ionic channels was indirectly estimated by proc essing the fluctuations of whole-cell current by means of an original parametric method. Mean conductance of the underlying channels was the n determined from the single-channel current estimated at different cl amp potentials. In the cells exhibiting small inward currents, the mea n conductance was equal to 0.5 +/- 0.2 pS (7 cells), whereas in the ce lls with large inward currents it was 3 +/- 0.4 pS (6 cells). This res ult gives a coherent explanation of the different kinds of responses o bserved at macroscopic level in the whole-cell current and confirms th at kainate-activated channels can exhibit different levels of conducta nce.