Relationships between capsaicin sensitivity of mammalian sensory neurons, cell size and type of voltage gated Ca-currents.

(1) The relationships between capsaicin sensitivity, cell size and the expression of voltage-dependent high-threshold (L- and N-type) and low-threshold (T-type) Ca-currents were investigated in cultured adult rat dorsal root ganglion neurons using the whole-cell patch-clamp technique. (2) The capsaicin (10 microM) evoked inward current was used to identify the capsaicin-sensitive population. To identify the voltage-dependent Ca-currents, the activation threshold and the inactivation kinetic were used. (3) In cultured dorsal root ganglion cells the capsaicin sensitivity is not restricted to the small cell population. About 28% of cells with large cross sectional areas (greater than or equal to 1001 microns 2) responded with about the same amplitude per micron2 cross sectional area as small cells. (4) The amplitude of the capsaicin evoked inward current depended on the length of time the cells were maintained in culture. (5) All cells exhibited the high-threshold Ca-currents. About 45% of the capsaicin-insensitive cells also had low-threshold Ca-currents. None of the capsaicin-sensitive cells had the low-threshold type. (6) Most of the cells which expressed the low-threshold type were in the upper size range.