RESTING MEMBRANE-POTENTIALS AND EXCITABILITY AT DIFFERENT REGIONS OF RAT DORSAL-ROOT GANGLION NEURONS IN CULTURE

To study the role of electrical membrane processes in neuronal regeneration and growth, resting membrane potentials and action potentials of sensory (dorsal root ganglion) neurons growing in culture were measured at the soma, neurite and growth cone using the whole-cell patch-clamp technique. Our results show that resting membrane potentials measured at the soma (-56.8 +/- 8.8 mV), neurite varicosity (-55.8 +/- 5.2 mV) and growth cone (-57.2 +/- 4.1 mV) of growing neurons were not statistically different. The membrane resistance measured around the resting membrane potential at the neurite varicosity (160 +/- 70 M Ohm) was smaller than those at the soma (687 +/- 540 M Ohm) and growth cone (922 +/- 825 M Ohm). The resting membrane potential measured at the soma using a perforated patch (-60.3 +/- 4.4 mV) was not different from that measured in the normal whole cell. In both configurations, isotonic KCl (140 mM) depolarized the membrane potential to above 0 mV. The K+ channel blockers quinine, Cs+, 4-aminopyridine and tetraethylammonium depolarized the membrane potential by 10-40 mV, while Na+-free extracellular solution hyperpolarized it by about 10 mV. Extracellularly applied ouabain, intracellular Na+-free or low Cl--containing solutions did not affect the resting membrane potential. Similar results were obtained for growth cones. Action potentials could be evoked by current pulses in 81% of somata and in all growth cones, but not in neurite varicosities. Current-induced repetitive firing was found in 19% of somata and in 65% of growth cones. The present results indicate identical resting potentials over the whole plasma membrane of process-forming dorsal root ganglion neurons in culture, but a variable expression of excitability at the soma, neurite and growth cone.