Figure 3.

Inhibitory effect of L-citrulline (0.01–47 mM) on diaphragm twitch tension induced by phrenic nerve stimulation (indirect stimulation, filled circles) or by direct muscle depolarization (direct stimulation, open circles) in conditions where the safety factor of neuromuscular transmission was reduced (high Mg²⁺, 6 mM). Twitch responses were induced alternating stimulus application to the phrenic nerve trunk or to muscle fibres at a frequency of 0.1 Hz. L-citrulline (0.01–47 mM) was applied in a cumulative manner; each concentration contacted the preparation at least 12 min before solution changeover. Ordinate, percentage change of the maximal twitch tension obtained in control conditions. Each point represents the mean±s.e.m. of six experiments. ^*P<0.05 (one-way ANOVA followed by Dunnett's modified t-test) compared with the effect of L-citrulline on twitch tension induced by direct muscle stimulation.