Spontaneous voltage and current fluctuations in tissue cultured mouse dorsal root ganglion cells

Abstract

Fetal mouse dorsal root ganglion (DRG) neurons were maintained in primary dissociated cell culture for periods of 7 days to 3 months. Intracellular recordings from these cells revealed the presence of spontaneous subthreshold potentials in 101/177 neurons studied. When measured at the resting membrane potential, these spontaneous voltage events took two forms: (a) high frequency potential fluctuations several millivolts in peak-to-peak amplitude and (b) small, discrete hyperpolarizations. Neurons exhibiting either type of event were designated as ‘active’ DRG cells. No spontaneous potentials were seen in DRG cells hyperpolarized to membrane voltages more negative than −64 ± 11.5 mV (n= 5cells). Under voltage-clamp conditions, the subthreshold potentials of active DRG cells were replaced by fluctuations in outward current. The power spectral density, S(f) of these current fluctuations was approximated by an equation of the form S(f)= (S(o)/[1 + (f/f c) α] where 2 ⩽ α ⩽ 3 and the half-power frequency f c= 11.3 ± 3.1 Hz at 23°C ( n = 17 cells). The spontaneous voltage fluctuations of active DRG cells were abolished in Ca 2+-free saline, and of the divalent metal cations Sr 2+, Mg 2+, Ba 2+, Co 2+ and Mn 2+, only Sr 2+ could substitute for Ca 2+ in the maintenance of this activity. Tetraethylammonium ions (1–10 mM) reversibly blocked the spontaneous potentials, while caffeine (10 mM) increased the frequency of these events. The spontaneous voltage fluctuations were not dependent on the presence of spinal cord neurons in the culture plate, and they were also observed in cultured DRG cells derived from adult mice.