Abstract
In vascular endothelial cells acetylcholine (ACh) increases [Ca2+]i which in turn activates charybdotoxin-sensitive IKCa, apamin-sensitive SKCa and ClCa channels. As a result, ACh induces a membrane hyperpolarization, but the response is sometimes transient and followed by the membrane depolarization. To investigate the possible mechanism for this variation, a sheet of endothelial cells was isolated from a guinea-pig mesenteric artery and perforated whole-cell clamp experiments using amphotericin B were performed. The intracellular Cl− concentration was modified by using either low-Cl− (20 mM) or high-Cl− (150 mM) pipette solutions. In the current clamp mode, application of ACh (0.5 μM) induced a large and sustained hyperpolarization when [Cl−]i was low, while the response was small and transient when [Cl−]i was high. In the voltage clamp mode in low [Cl−]i condition, the reversal potential of ACh-induced current was -54.1 mV and it was changed to -27.8 mV after the K conductance was blocked by charybdotoxin and apamin. On the other hand, the reversal potential was changed from -57.8 mV to -76.0 mV by blocking Cl conductance with DIDS. When [Cl−]i was high, the reversal potential was -22.0 mV and it was changed to -0.6 mV after the K channels were blocked. These results indicate that enhanced Ca2+-activated Cl− current modifies ACh-induced hyperpolarization to be small and transient when the [Cl−]i is increased in some pathological conditions. [J Physiol Sci. 2006;56 Suppl:S143]
