Current-clamp properties of DRG neurons transfected with I228M. Excitability of DRG neurons expressing I228M: (A) RMP of DRG neurons expressing WT (-58.5 ± 1.4, n = 22) or I228M (-53.7 ± 1.7, n = 12); *p < 0.05. (B) Current threshold of DRG neurons expressing WT (121 ± 27, n = 22) or I228M (124 ± 28, n = 12) to 200 msec stimuli. (C) Comparison of mean firing frequency in DRG neurons expressing WT and I228M across a range of current injections from 50 to 500pA; *p < 0.05. (D) Bar graph showing the proportion of spontaneous firing cells for DRG neurons expressing I228M (red) and WT channels (black); numbers to the right of the bar graph show values for WT (lower value in parentheses) and I228M (upper value); *p < 0.05. The recording on the right shows spontaneous firing (10 seconds) of representative DRG neuron expressing I228M; the numbers above the trace show average ± standard deviation frequency of spontaneous action potentials. APs = action potentials.