Figure 5. Comparison of nerve-evoked junction potentials in the WT and W/W^v mouse IAS in the absence of atropine.

(A) Sample traces showing the effects of MRS2500 and L-NNA on junction potentials elicited with 5 Hz EFS (10 s) in WT (Aa) and W/W^v (Ab) mice in the absence of atropine. The inhibition of IJPs by MRS2500 (1 μM) in the absence of atropine (2^nd traces) was similar to that seen in the presence of atropine (see Fig. 3A, middle traces). However, with combined addition of L-NNA and MRS2500 a slow depolarization is revealed in WT but not W/W^v mice (3^rd traces). This depolarization is abolished by atropine (1 μM; 4^th traces). (B) Summary graph of the effects of MRS2500 and L-NNA in the absence of atropine on junction potentials during 3 different time periods in WT (Ba) and W/W^v (Bb) mice. IJPs elicited under control conditions (■, n= 6 WT; n=5 W/W^v) were significantly (*) reduced by MRS2500 (□, n= 6 WT; n= 5 W/W^v) in both animals. The IJP remaining in the presence of MRS2500 in W/W^v mice was significantly smaller (@) than in WT mice. In both animals IJPs were abolished (#) by combined addition of MRS2500 and L-NNA (○, n= 5 WT; n=5 W/W^v) revealing a 5 mV depolarization in WT mice that was absent from W/W^v mice (&). Atropine abolished ($) the slow depolarization in WT mice (●, n= 5 WT; n=5 W/W^v). All muscles were pre-exposed to 25 μM wortmannin for 20 min followed by at least 1 hour wash out before beginning experiments. Shown are mean values ± S.E.M.