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. 2019 Sep 18;151(10):1213–1230. doi: 10.1085/jgp.201912374

Figure 5.

Figure 5.

MRC sensitivity depends on stimulus position. (A) Experimental (left) and simulated (right) normalized peak MRC–displacement curves in response to stimuli delivered anterior (blue) and posterior (red) to the cell body. Peak MRCs were normalized to the current evoked by a 10-µm displacment (norm.), pooled, and averaged (blue, anterior; red, posterior). Experimental points are mean ± SEM for n = 22 worms with anterior stimulation (blue, same recordings as in Fig. 3 A) and n = 12 worms with posterior stimulation (red, stimulator positioned a mean ± SD of 61 ± 12 µm posterior to the ALM cell body with range 48–89 µm, recordings indicated in Fig. 4 B). Simulated traces (right) show predicted normalized peak currents for stimuli delivered anterior (blue, 50 µm from cell body) and posterior (pink, 25 µm; red, 50 µm) to cell body. (B) Experimental (left) and simulated (right) relationship between total MRC charge and displacement, derived from the experimental and simulated data in A. Total MRC charge was normalized to the charge transferred in response to a 10-µm displacement (norm.), pooled, and averaged (blue, anterior; red, posterior). (C) The time to reach half-maximal current is similar in anterior and posterior (left) recordings, but diverges in simulations (right). (D) The decay half-time increases with displacement for anterior, but not posterior recordings (left), a distinction that is not reproduced in simulations (right). Experimental results in C and D were limited to recordings obtained with the stimulator positioned within 90 µm of the cell body (indicated in Fig. 4 B, gray) and include a total of n = 7 (anterior) and n = 11 (posterior) recordings. Error bars are SEM in A, B, C, and D. (E) The simulated mean peak current per active channel is lower for stimuli delivered posterior to the cell body than it is for the anterior stimuli. (F) Simulations reveal that stimuli recruit channels only if the displacement is large. The threshold of 0.1 × io for active channels includes both open and subconducting channels.