Histamine Induces K+,Ca2+, andCl-Currents inHumanVascular Endothelial Cells RoleofIonic Currents inStimulation of Nitric OxideBiosynthesis

Thenature ofthemembrane currents mediating agonist-induced Ca'+ entry andenhanced nitric oxide (NO) production inendothelial cells isstill unclear. Usingboth perforated-patch andconventional whole-cell clamptech- nique, wehavestudied themembraneresponse associated withhistamine stimulation ofhumanvascular endothelial cells. Inperforated-patch experiments, theinitial histamine (10 ,umol/L)-induced current reversed close totheK'equilibrium potential andwasblocked bytetrabutylammonium ions (TBA, 10mmol/L). Inaddition, a TBA-insensitive current that developed slowly inthepresence ofhistamine wasrecorded. Thisdelayed histamine-induced current reversed close to neutral potential andwasinhibited bySK&F 96365(25 ,umol/L), aputative blocker ofreceptor-operated Ca2+chan- nels. Similar histamine effects wereobserved inconventional whole-cell experiments using pipette solutions withlowCa'+- buffering capacity. Strong buffering ofintracellular free Ca2 suppressed theinitial, butnotthedelayed, current response. Thedelayed component ofhistamine-induced current was substantially inhibited bytheCl-chaii.iel blocker N-phenylan- A gonist-induced Ca2'entry isamajor determinant ofvascular endothelial functions. Inparticular, theformation ofendothelium-derived relaxing