Kinetic properties of mechanically activated currents in spinal sensory neurons

Dorsal root ganglion neurons in vitro express a number of types of mechanically activated currents that are thought to underlie somatic mechanosensory transduction in vivo. We have studied the inactivation properties of these currents to assess how they might influence the electrophysiological responses of dorsal root ganglion (DRG) neurons to mechanical stimulation. We show that the speed of ramp-like mechanical stimulation determines the dynamics of mechanically activated current responses and hence the type of DRG neuron most likely to be activated. We also show that both rapidly and slowly adapting currents inactivate as a function of membrane stretch. However, the rapidly adapting current inactivation time course is mainly dependent on channel opening whilst slowly adapting current kinetics are dependent on membrane stretch. In response to repeated stimulation, slowly adapting currents inactivate less and recover more quickly than rapidly adapting currents. Therefore, vibratory stimuli tend to inactivate rapidly adapting currents whilst static stimuli tend to inactivate slowly adapting currents. Current clamp experiments show that, physiologically, the response of different types of sensory neurons is dictated primarily by the static or dynamic nature of the mechanical stimulus and the interplay between voltage-gated and mechanically gated ion channels expressed in these neurons.