Figure 3.

Smooth muscle hyperpolarization and relaxation to ACh during depolarization and contraction to U46619. (a) Simultaneous measurement of changes in smooth muscle membrane potential (upper panel) and relaxation (lower panel) in mesenteric arteries during U46619 (10 nM–0.1 μM) stimulation. Increases in the membrane potential and relaxation with ACh, showed progressive reduction during the second and third stimulation with U46619. By the third exposure, membrane potential did not overshoot the original resting value, ^*P<0.05, ANOVA with Bonferroni multiple comparisons test, n=5. Resting membrane potential (rmp) for each group is shown in the left segment of the graph. A small but significant reduction in relaxation was observed during the third stimulation with U46619. The ACh hyperpolarization and relaxation was completely blocked in the presence of 50 nM apamin and 100 nM charybdotoxin combined. (b) Cumulative % relaxation to ACh in U46619 stimulated mesenteric arteries. Membrane potential was not recorded during these experiments. Relaxation to ACh during a forth stimulation with U46619 (n=6) was completely blocked with charybdotoxin alone, without a requirement for apamin (^*P<0.05, n=5, Bonferroni multiple comparisons test).