Imaging stochastic spatial variability of active channel clusters during excitation of single neurons

Topographical maps of membrane voltages were obtained during action potenti als by imaging, at 1 mum resolution, live dissociated neurons stained with the voltage sensitive dye RH237. We demonstrate with a theoretical approach that the spatial patterns in the images result from the distribution of ne t positive charges condensed in the inner sites of the membrane where clust ers of open ionic channels are located. We observed that, in our biological images, this spatial distribution of open channels varies randomly from tr ial to trial while the action potentials recorded by the microelectrode dis play similar amplitudes and time-courses. The random differences in size an d intensity of the spatial patterns in the images are best evidenced when t he time of observation coincides with the duration of single action potenti als. This spatial variability is explained by the fact that only part of th e channel population generates an action potential and that different chann els open in turn in different trials due to their stochastic operation. Suc h spatial flicker modifies the direction of lateral current along the neuro nal membrane and may have important consequences on the intrinsic processin g capabilities of the neuron. (C) 2001 Elsevier Science Ireland Ltd and the Japan Neuroscience Society. All rights reserved.