Histamine increases [Ca2+](in) and activates Ca-K and nonselective cation currents in cultured human capillary endothelial cells

We characterized the effects of histamine on intracellular Ca2+ and activat ion of ionic currents in human capillary endothelial cells. Histamine produ ced both a transient and sustained increase in intracellular Ca2+. The tran sient response was mediated largely through intracellular Ca2+ release and the sustained response was due to extracellular Ca2+ entry. Tile increase i n intracellular Ca2+ by histamine was not affected by the H2 blocker cimeti dine. But was entirely blocked by the H1 antagonist diphenhydramine showing that the histamine response in these cells is mediated through the H1 rece ptor. A transient ionic current is coactivated with the histamine-induced i ncrease in intracellular Ca2+ and this current has several properties of a nonselective, Ca2+ permeable, cation channel (NSC). The magnitude of the NS C current does not strictly correlate with intracellular Ca2+ levels. A Ca2 +-activated Kf current (BKCA:) is activated by the increase in intracellula r Ca2+ and this current is blocked by the selective BKCA blocker iberiotoxi n.