[The electrical reactions of endothelial cells in situ to ATP action]

The changes in the membrane potential (MP) of in situ endothelial cells from guinea pig aorta was studied using patch-champ technique under ATP stimulation. Extracellular ATP is shown to evoke the complex changes in endothelial MP: initial short-lived depolarization and subsequent maintained hyperpolarization. Extracellular calcium buffering as well as addition of extracellular Ni2+ made the hyperpolarization shorter. After the buffering of intracellular calcium ATP addition evoked only depolarization which was not observed in the absence of extracellular sodium. The hyperpolarization under ATP stimulation was absent after emptying of intracellular calcium stores. It was concluded that hyperpolarization in response to ATP is initiated by calcium release from intracellular stores followed by activation of calcium-dependent potassium channels, the maintained phase of hyperpolarization is provided by extracellular calcium entry and initial depolarization by extracellular sodium entry into EC.