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. 2020 Feb 20;117(10):5494–5501. doi: 10.1073/pnas.1911382117

Fig. 3.

Fig. 3.

RIIIJ enhanced firing in L1 and L2 neurons. (A) [Ca2+]i response from an L1 DRG neuron identified by the prototypical smooth DE to the application of RIIIJ. (B) [Ca2+]i response from an L2 neuron identified by its prototypical jagged response to the application of RIIIJ. Three 15-s depolarizing stimuli of 20 mM K+(indicated by arrows) were applied at 7-min intervals. The application of 1 μM RIIIJ (gray bar) elicited a direct increase in [Ca2+]i in both L1 and L2 neurons. These two DRG neurons were patched, and electrophysiological recordings were obtained in current-clamp mode. (C) Current-clamp recordings from L1 neuron shown in A. The membrane potential of the neuron was monitored at a holding current of 0 pA and to current injections −100, 0, +25, and +100 pA in the absence (left traces) and presence (right traces) of 1 μM RIIIJ. RIIIJ induced repetitive APs, and the frequency of firing increased during positive current injections (+25 and +100 pA), while APs were totally suppressed during a −100-pA injection. (D) Current-clamp recordings from L2 neuron shown in B. The membrane potential of the L2 neuron was monitored at a holding current of 0 pA and to current injections −100, 0, +25, and +100 pA in the absence (left traces) and presence (right traces) of 1 μM RIIIJ. In both neurons, the frequency of firing increased significantly with the increase in positive current injections (+25- and +100-pA steps) in the presence of RIIIJ. In contrast to L1 neurons, L2 neurons did not display tonic firing at 0 pA and displayed a small difference in the number of APs with increase in current injections (no significant difference between +50 and +200 pA). These observations are quantified in E and F for L1 and L2 neurons, respectively. Black bars represent a 500-ms duration when current steps were applied. The y axis represents membrane potential (scale ranges from −150 to +50 mV for all traces). n = 10 cells in each group. ***P < 0.005 as determined by two-way ANOVA test on Graphpad Prism; ****P < 0.0001 as determined by two-way ANOVA test on Graphpad Prism.