Distinct mechanosensitive properties of capsaicin-sensitive and -insensitive sensory neurons.

Mechanical stimulation of the somata of cultured neonatal rat dorsal root ganglia (DRG) neurons evoked inward cationic currents that displayed distinct properties between different subsets of cells. The presumptive nociceptor population, defined by capsaicin sensitivity, showed higher thresholds for the induction of an inward current and lower peak currents than other mechanosensitive neurons. A subset of capsaicin-sensitive IB4-positive sensory neurons was refractory to mechanical stimulation. All mechanically activated currents were blocked by gadolinium (IC50 approximately 8 microm) and ruthenium red (IC50 approximately 3 microm). Disruption of the actin cytoskeleton by acute application of 10 microm cytochalasin B inhibited currents much more effectively in capsaicin-insensitive (61%) than capsaicin-sensitive neurons (20%). Extracellular calcium also attenuated mechanosensitive currents and to a greater degree in capsaicin-insensitive neurons than capsaicin-sensitive neurons. These data demonstrate that the somata of different types of cultured sensory neurons have distinct mechanosensitive phenotypes that retain properties associated with nerve terminal mechanosensors in vivo.