Figure 10

S1P does not evoke a change in membrane current in small-diameter sensory neurons. (A) Left panel shows a representative current-clamp recording where the ramp of depolarizing current evoked 3 APs in a small-diameter capsaicin-sensitive rat sensory neuron. The right panel shows the membrane current (holding voltage −60 mV) in response to a 60-s bath application of 1 μM S1P; the trace shows points at 20-ms intervals in order to reduce the dataset size; the inset represents an expanded portion of the current (35 to 235 s). (B) Left panel demonstrates a representative current-clamp recording where the ramp of depolarizing current evoked 2 APs in a small-diameter capsaicin-sensitive mouse sensory neuron. The right panel shows the membrane current (holding voltage −60 mV, 20-ms interval) in response to a 60-s bath application of 1 μM S1P. (C) Left panel shows that the ramp evokes 4 APs in this small-diameter capsaicin-sensitive mouse sensory neuron. The right panel shows the membrane current (holding voltage −60 mV, 20-ms interval) in response to a 60-s bath application of 100 μM S1P. In the left panels, the dotted line represents the 0 mV level; in the right panels, the line noted with 0 marks the zero-current level. (D) Medium- to large-diameter sensory neurons are not sensitized by S1P. Exposure of medium- to large-diameter sensory neurons isolated from rat DRG to 1 μM S1P by either bath superfusion (n = 7) or micro-injection of a stock into the bath (n = 8) does not alter the excitability. AP - action potential, Cont - control, S1P - sphingosine-1-phosphate.