Low-frequency voltage noise in a mammalian bone cell clone.

Measurements were made of plasma membrane voltage noise in cells of a bone cell clone. The measurements were made under conditions intended to approximate in vivo conditions more closely than in previous electrical measurements on small mammalian cells. Mononucleate cells of normal size, imbedded in a collagen matrix, were used. The electrical state of the cell membrane under normal conditions was characterized by low-frequency random fluctuations (noise) of high magnitude. Hyperpolarizing spikes were observed in some cells. Power spectrum analysis revealed that the random fluctuations were actually a sum of incoherent spike patterns, with spikes of the same time width as those seen in the clearly spiking patterns. This analysis, combined with similar measurements in a high [K+], low [Na+] medium, showed that the fluctuation/spiking phenomenon resulted from modulation of K+ and Na+ transport by a control process at a level higher than that of the individual channels. This process persisted when the membrane potential was depolarized. These results indicate that the membrane potential is not part of the feedback loop producing the fluctuation/spiking phenomenon.