Figure 3.

The effect of increasing the K⁺ concentration on the response to acetylcholine (ACh). These experiments were performed in the presence of 100 μM L-NOARG and 10 μM indomethacin so that the involvement of nitric oxide and the cyclo-oxygenase pathway of the arachidonic acid cascade could be excluded. The K⁺ concentration in the modified Tyrode's solution was increased to 20 mM (•), 30 mM (▴) and to 40 mM (▪). The noradrenaline concentration was 5 μM in the control, 3 μM in the K⁺ 20 mM, 2 μM in the K⁺ 30 mM, and 1 μM in the K⁺ 40 mM Tyrode's solution was used to adjust the contraction amplitude. Data are means±s.e.mean from 12 preparations. Relaxations of ACh of the concentrations higher than 10 nM were significantly smaller in the presence of elevated K⁺ than control (5.4 mM K⁺). The others are the same as those in Figure 1.