From these parameters, we estimate that the time required to move the probe is 1.3 ms. Thus, the latency for channel activation is 2.1 ms or less. This latency is longer than the shortest latencies measured for other C. elegans neurons ( O’Hagan et al., 2005 and Kang

et al., 2010), but, because the fastest known second messenger-based sensory transduction pathway has a latency of 20 ms ( Hardie, 2001), we propose that this latency is brief enough to suggest that force acts directly on the MeT channels that carry MRCs in ASH. Sinusoidal oscillations were detected in many of our MRC recordings Compound Library suggesting that channel activation is able to follow the rapid, resonant movements of the probe (Figure 1B). To determine the frequency of MRC oscillations, we fit the total MRC with an alpha function and subtracted this fit from the average current to isolate the sinusoidal variations in current (Figure 1B). In five recordings with high-quality oscillations, the MRC oscillation frequency had an average value of 130 ± 6 Hz (mean ± SEM, n = 5). Thus, channels carrying MRCs in the ASH neurons can follow rapid variations in applied mechanical loads. Mechanoreceptor currents, if mediated by a DEG/ENaC channel complex, should be carried by Na+ ions and blocked by amiloride. Conversely, if MRCs were carried by a TRPV channel complex, they should be permeable to both Na+

and K+ and resistant to amiloride. Wild-type MRCs were reversibly

Selleck BIBW2992 blocked by amiloride (Figures 2A and 2B). The fraction of peak current blocked by 300 μM amiloride was 0.77 ± 0.06 (n = 4) and 0.75 ± 0.10 (n = 3) at −90 and −60 mV, respectively. This same level of MRC block was achieved in the gentle touch receptor neuron PLM that expresses the DEG/ENaC channel subunits MEC-4 and MEC-10 with 200 μM amiloride (O’Hagan et al., 2005). MRCs in ASH may be carried by DEG/ENaC channels that are more resistant to amiloride than MEC-4 and MEC-10 or ASH may express a distinct population of channels that is insensitive to amiloride. Below, we provide evidence that MRCs are carried by two classes of ion channels. The ASH neurons terminate in a single cilium before that extends into the external environment through an opening in the amphid (Perkins et al., 1986). If the MeT channels localize to this cilium, then exogenous amiloride should inhibit behavioral responses to nose touch. Consistent with this prediction, animals exposed to amiloride for more than 30 min showed a modest but statistically significant decrease in sensitivity to nose touch (Figure 2C). Such a minor effect on nose touch sensitivity is the expected result for two reasons. First, 300 μM amiloride does not completely block MRCs (Figures 2A and 2B). Second, ASH is not the only mechanoreceptor neuron responsible for sensitivity to nose touch (Kaplan and Horvitz, 1993), but it is the only one exposed to the external environment.