Contribution of surface potential to resting potential in mouse neuroblastoma cells: estimation with fluorescent dyes and from shift of threshold potential for Ca-spike

Abstract

The contribution of the changes in the diffuse double layer potential (surface potential) to the resting membrane potential of the mouse neuroblastoma (N-18 clone) was estimated with the use of fluorescent dyes and from the shift of the threshold potential of the Ca-spike. The membrane potential monitored by Rhodamine 6G was unchanged with variations of external K+ concentration [( K+]o) below about 10 mM, and changed linearly with log [K+]o above this concentration, similar to the changes observed with a microelectrode. This result indicates that the independence of the membrane potential of [K+]o at low [K+]o is not brought about by the artifacts caused by insertion of a microelectrode into the cell. The changes in the surface potential in response to various polyvalent cations (Mg2+, Ca2+, Mn2+, Cd2+ and La3+) were monitored by the fluorescence of ANS. The behavior of the surface potential thus observed was closely correlated with that of the membrane potential for the respective polyvalent cations. The surface potential changes in response to increase in [Ca2+]o from 1.8 to 100 mM and in [Mg2+]o from 0.8 to 100 mM were 88% and 85% in magnitude compared with the corresponding changes in the membrane potential, respectively. The effect of variation of [Ca2+]o on the threshold potential of the Ca-spike was compared with that of [Ca2+]o on the resting membrane potential. The magnitude of the surface potential change determined by the shift of the threshold potential was comparable to the magnitude of the membrane potential change. The results in the present study suggest that the surface potential change produced at the membrane surface of N-18 cells is detected as a transmembrane potential change without a large reduction in magnitude.