Impulses of variable amplitude recorded from cell-attached patches on small hippocampal neurons

Small cultured neurons from embryonic rat hippocampus were investigated with the cell-attached configuration of the patch-clamp technique. The currents associated with spontaneous cellular impulse generation were studied. The positive peak current amplitudes varied by a factor larger than 2.5 for 11 of 12 cells quantitatively investigated, suggesting underlying action potentials of variable amplitude. A simple RC-network was found to describe the properties of the patch membrane, and was used to calculate the underlying potential time course. The action potentials computed showed a considerable variation in amplitude. The results suggest that the impulse variability previously analysed with the whole-cell technique was not caused by dialysis of the cell interior.