Abstract
Effects of acetylcholine (ACh) on the membrane potential and current recorded from endothelial cells dispersed from the rabbit aorta were investigated using the patch-clamp technique. ACh hyperpolarized the endothelial cell membrane. Using the whole-cell voltage-clamp procedure, ACh (1CT-6 M) induced an outward current, and this current was blocked by atropine (1CT-6 M). Application of either pirenzepine (3×10-7 M) or AF-DX 116 (3×10-6 M) slightly inhibited the ACh-induced outward current, and simultaneous application of these two blockers markedly inhibited the outward current. Application of caffeine (2×10-2 M), ryanodine (10-5 M) or heparin (10-5 g/ml) reduced the amplitude of the ACh-induced outward current. A single-channel current recording using the patchclamp technique revealed that ACh opens a Ca-dependent K-channel with a single-channel current conductance of 9 pS. These results indicate that both M1 and M2 receptor subtypes are present in endothelial cells of the rabbit aorta and that ACh activates the Ca-dependent K channel via release of Ca from intracellular store sites. In addition, methylene blue inhibited the ACh-induced outward current from the outside membrane.
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