Analysis of acetylcholine-induced membrane responses in vascular endothelial cells of the guinea-pig mesenteric artery using mefloquine as a gap junction blocker.

Acetylcholine (ACh)-induced membrane currents were investigated using freshly isolated endothelial layers prepared from the guinea-pig mesenteric artery. Gap junctions were blocked by mefloquine and the whole-cell patch clamp method was applied to individual endothelial cells within each multicellular preparation. While mefloquine effectively blocked the gap junctions, it hyperpolarized the membrane by some 10 mV. As this hyperpolarization was absent when the intracellular Cl(-) concentration was increased, mefloquine may increase the membrane conductance for Cl(-). Besides this minor hyperpolarizing effect, mefloquine did not have serious side effects and ACh could activate a sustained outward current producing a membrane hyperpolarization at concentrations as low as 100 nM. At the beginning of ACh application, the reversal potential of the ACh-induced current was around the equilibrium potential for K(+) indicating that this was a K(+) current. The reversal potential then gradually became less negative suggesting that other ionic conductances with less negative equilibrium potentials were involved. As the ACh-induced outward current was completely blocked by charybdotoxin (CTX, 100 nM), this current seemed to be due to CTX-sensitive K(+) channels, possibly IK(Ca) channels. After the K(+) current had been blocked, ACh gradually activated the membrane current which reversed the polarity at around -10 mV, which was most likely due to Ca(2+)-activated non-selective cation channels. These ionic conductances may be responsible for the variety in agonist-induced membrane responses observed in different types of vascular preparations.